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Moved page from wikipedia:en:Abiogenesis (history)

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{{short description|The natural process by which life arises from non-living matter}}

{{Redirect|Origin of life|non-scientific views on the origins of life|Creation myth}}

{{distinguish|Biogenesis}}

{{For|the oldest life forms| Earliest known life forms}}

{{Use dmy dates|date=June 2020}}



< ! ——发布日期使用 dmy，但是归档和访问日期使用 mosdate -- > 允许的 ymd

{{Use American English|date=December 2019}}

[[File:Champagne vent white smokers.jpg|thumb|upright=1.5|The [[earliest known life forms|earliest known life-forms]] on [[Earth]] are putative fossilized [[microorganism]]s, found in [[Hydrothermal vent|hydrothermal vent precipitates]], that may have lived as early as 4.28 Gya (billion years ago), relatively soon after the [[ocean]]s [[Origin of water on Earth#Water in the development of Earth|formed 4.41 Gya]], and not long after the [[Age of the Earth|formation of the Earth]] 4.54 Gya.<ref name="NAT-20170301" /><ref name="NYT-20170301" />]]

earliest known life-forms on Earth are putative fossilized microorganisms, found in hydrothermal vent precipitates, that may have lived as early as 4.28 Gya (billion years ago), relatively soon after the oceans formed 4.41 Gya, and not long after the formation of the Earth 4.54 Gya. is the natural process by which life has arisen from non-living matter, such as simple organic compounds. While the details of this process are still unknown, the prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but an evolutionary process of increasing complexity that involved molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. Although the occurrence of abiogenesis is uncontroversial among scientists, its possible mechanisms are poorly understood. There are several principles and hypotheses for abiogenesis could have occurred.

地球上已知最早的生命形式是假定的化石微生物，发现于深海热泉沉淀物中，可能存在于早在4.28 Gya (10亿年前) ，在海洋形成4.41 Gya 后不久，也就是在地球形成后不久。是生命从非生命物质(如简单的有机化合物)中产生的自然过程。虽然这个过程的细节仍然是未知的，主流的科学假说是从非生命体到生命体的转变不是一个单一的事件，而是一个日益复杂的进化过程，涉及到分子自我复制、自组装、自我催化和细胞膜的出现。虽然自然发生的发生在科学家中是没有争议的，但其可能的机制却知之甚少。关于自然发生可能有几个原理和假说。



In [[evolutionary biology]], '''abiogenesis''', or informally the '''origin of life''' (OoL),<ref>{{cite book| last1 = Oparin| first1 = Aleksandr Ivanovich| author-link1 = Alexander Oparin| translator1-last = Morgulis| translator1-first = Sergius| year = 1938| title = The Origin of Life| url = https://books.google.com/books?id=Jv8psJCtI0gC| series = Phoenix Edition Series| edition = 2| location = Mineola, New York| publisher = Courier Corporation| publication-date = 2003| isbn = 978-0486495224| access-date = 2018-06-16}}</ref><ref name=Pereto /><ref name="AST-20151218">Compare: {{cite journal |author= Scharf, Caleb |title= A Strategy for Origins of Life Research |date= 18 December 2015 |journal= [[Astrobiology (journal)|Astrobiology]] |volume= 15 |issue= 12 |pages= 1031–1042 |doi= 10.1089/ast.2015.1113 |display-authors= etal |pmid= 26684503 |pmc= 4683543|bibcode= 2015AsBio..15.1031S | quote = What do we mean by the origins of life (OoL)? [...] Since the early 20th century the phrase OoL has been used to refer to the events that occurred during the transition from non-living to living systems on Earth, i.e., the origin of terrestrial biology (Oparin, 1924; Haldane, 1929). The term has largely replaced earlier concepts such as abiogenesis (Kamminga, 1980; Fry, 2000).}}</ref>{{efn|Also occasionally called biopoiesis (Bernal, 1960, p. 30)}} is the [[natural]] process by which [[life]] has arisen from non-living matter, such as simple [[organic compound]]s.<ref name=Oparin>{{harvnb|Oparin|1953|p=vi}}</ref><ref name=Pereto>{{cite journal|last= Peretó |first= Juli |year= 2005 |title= Controversies on the origin of life |url= http://www.im.microbios.org/0801/0801023.pdf |journal= [[International Microbiology]] |volume= 8 |issue= 1 |pages= 23–31 |pmid= 15906258 |accessdate= 2015-06-01 |url-status= dead |archiveurl= https://web.archive.org/web/20150824074726/http://www.im.microbios.org/0801/0801023.pdf |archivedate= 24 August 2015 |quote = Ever since the historical contributions by Aleksandr I. Oparin, in the 1920s, the intellectual challenge of the origin of life enigma has unfolded based on the assumption that life originated on Earth through physicochemical processes that can be supposed, comprehended, and simulated; that is, there were neither miracles nor spontaneous generations.}}</ref><ref>{{cite journal |last1= Warmflash |first1= David |last2= Warmflash |first2= Benjamin |date= November 2005 |title= Did Life Come from Another World? |journal= [[Scientific American]] |volume= 293 |issue= 5 |pages= 64–71 |doi= 10.1038/scientificamerican1105-64|pmid= 16318028 |bibcode= 2005SciAm.293e..64W | quote = According to the conventional hypothesis, the earliest living cells emerged as a result of chemical evolution on our planet billions of years ago in a process called abiogenesis.}}</ref><ref>{{harvnb|Yarus|2010|p=47}}</ref> While the details of this process are still unknown, the prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but an evolutionary process of increasing complexity that involved molecular [[self-replication]], [[self-assembly]], [[autocatalysis]], and the emergence of [[cell membrane]]s.<ref>{{cite journal|url=http://www.biocommunication.at/pdf/publications/biosystems_2016.pdf |title=Crucial steps to life: From chemical reactions to code using agents|journal=Biosystems|volume=140|pages=49–57|doi=10.1016/j.biosystems.2015.12.007|pmid=26723230|year=2016|last1=Witzany|first1=Guenther}}</ref><ref name="AB-20141208">{{cite web |last= Howell |first= Elizabeth |title= How Did Life Become Complex, And Could It Happen Beyond Earth? |url= https://www.astrobio.net/origin-and-evolution-of-life/life-become-complex-happen-beyond-earth/ |date= 8 December 2014 |work= [[Astrobiology Magazine]] |accessdate= 14 February 2018 }}</ref><ref name="EA-20150420">{{Cite book |last= Tirard |first= Stephane |title= Abiogenesis – Definition|date= 20 April 2015 |doi= 10.1007/978-3-642-27833-4_2-4 |journal= Encyclopedia of Astrobiology|pages= 1 | quote = Thomas Huxley (1825–1895) used the term abiogenesis in an important text published in 1870. He strictly made the difference between spontaneous generation, which he did not accept, and the possibility of the evolution of matter from inert to living, without any influence of life. [...] Since the end of the nineteenth century, evolutive abiogenesis means increasing complexity and evolution of matter from inert to living state in the abiotic context of evolution of primitive Earth.

The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. It primarily uses tools from biology, chemistry, and geophysics, with more recent approaches attempting a synthesis of all three: more specifically, astrobiology, biochemistry, biophysics, geochemistry, molecular biology, oceanography and paleontology. Life functions through the specialized chemistry of carbon and water and builds largely upon four key families of chemicals: lipids (cell membranes), carbohydrates (sugars, cellulose), amino acids (protein metabolism), and nucleic acids (DNA and RNA). Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules. Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. Researchers generally think that current life descends from an RNA world,

这项关于自然发生的研究旨在确定生命前的化学反应是如何在与今天地球截然不同的条件下产生生命的。它主要使用来自生物学、化学和地球物理学的工具，最近的方法试图综合这三个学科: 更具体地说，天体生物学、生物化学、生物物理学、地球化学、分子生物学、海洋学和古生物学。生命通过碳和水的特殊化学作用，主要建立在四种关键化学物质上: 脂类(细胞膜)、碳水化合物(糖、纤维素)、氨基酸(蛋白质代谢)和核酸(DNA 和 RNA)。任何成功的自然发生理论都必须解释这些类分子的起源和相互作用。许多自然发生的方法研究自我复制的分子或其组成部分是如何形成的。研究人员普遍认为现在的生命起源于 RNA 世界,

|isbn= 978-3-642-27833-4 }}</ref> Although the occurrence of abiogenesis is uncontroversial among scientists, its possible mechanisms are poorly understood. There are several principles and hypotheses for {{em|how}} abiogenesis could have occurred.<ref>{{Cite book |title=Rethinking evolution: the revolution that's hiding in plain sight |last=Levinson |first=Gene |publisher=World Scientific |year=2020 |isbn=978-1786347268 |url=https://rethinkingevolution.com/}}</ref>

The alternative panspermia hypothesis speculates that microscopic life arose outside Earth by unknown mechanisms, and spread to the early Earth on space dust and meteoroids. It is known that complex organic molecules occur in the Solar System and in interstellar space, and these molecules may have provided starting material for the development of life on Earth.

另一种胚种假说推测，微生物通过未知的机制在地球以外产生，并通过太空尘埃和流星体传播到早期地球。众所周知，复杂的有机分子存在于太阳系和星际空间，这些分子可能为地球上生命的发展提供了起始物质。

The study of abiogenesis aims to determine how pre-life [[chemical reaction]]s gave rise to life under conditions strikingly different from those on Earth today.<ref>{{harvnb|Voet|Voet|2004|p=29}}</ref> It primarily uses tools from [[biology]], [[chemistry]], and [[geophysics]],<ref name="Dyson 1999">{{harvnb|Dyson|1999}}</ref> with more recent approaches attempting a synthesis of all three:<ref>{{cite book |author= Davies, Paul |date= 1998 |title= The Fifth Miracle, Search for the origin and meaning of life |publisher= Penguin}}{{page needed|date=February 2017}}</ref> more specifically, [[astrobiology]], [[biochemistry]], [[biophysics]], [[geochemistry]], [[molecular biology]], [[oceanography]] and [[paleontology]]. Life functions through the specialized chemistry of [[carbon]] and [[water]] and builds largely upon four key families of chemicals: [[lipids]] (cell membranes), [[carbohydrates]] (sugars, cellulose), [[amino acid]]s (protein metabolism), and [[nucleic acids]] (DNA and RNA). Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules.<ref>{{cite book |author1= Ward, Peter|author2= Kirschvink, Joe |date= 2015 |title= A New History of Life: the radical discoveries about the origins and evolution of life on earth |publisher= Bloomsbury Press |pages= 39–40 |isbn= 978-1608199105}}</ref> Many approaches to abiogenesis investigate how [[Self-replication|self-replicating]] [[molecule]]s, or their components, came into existence. Researchers generally think that current life descends from an [[RNA world]],<ref name="RNA" /> although other self-replicating molecules may have preceded RNA.<ref name="Robertson2012" /><ref name="Cech2012" />

Earth remains the only place in the universe known to harbour life, and fossil evidence from the Earth informs most studies of abiogenesis. The age of the Earth is 4.54 Gy (Giga or billion year); the earliest undisputed evidence of life on Earth dates from at least 3.5 Gya (Gy ago), and possibly as early as the Eoarchean Era (3.6-4.0 Gya). In 2017 scientists found possible evidence of early life on land in 3.48 Gyo (Gy old) geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton of Western Australia. However, a number of discoveries suggest that life may have appeared on Earth even earlier. , microfossils (fossilised microorganisms) within hydrothermal-vent precipitates dated 3.77 to 4.28 Gya in rocks in Quebec may harbour the oldest record of life on Earth, suggesting life started soon after ocean formation 4.4 Gya during the Hadean Eon.

地球仍然是宇宙中已知存在生命的唯一地方，来自地球的化石证据为大多数关于自然发生的研究提供了依据。地球的年龄是4.54 Gy (千兆或十亿年) ; 地球上生命存在的最早无可争议的证据可以追溯到至少3.5 Gya (吉前) ，可能还要追溯到早期太古代(3.6-4.0 Gya)。2017年，科学家在西澳大利亚的 Pilbara Craton 发现了3.48 Gyo (Gy old) geyserite 和其他相关矿藏(通常在温泉和间歇泉附近发现) ，并找到了陆地上早期生命存在的可能证据。然而，许多发现表明，地球上的生命可能出现得更早。在加拿大魁北克省的岩石中，热液喷口沉淀物中的微化石(微生物化石)的年龄可能在3.77至4.28 Gya 之间，这可能是地球上最古老的生命记录，表明生命是在海洋形成后不久开始的。

[[File:Miller-Urey experiment JP.png|thumb|'''Miller–Urey experiment''' Synthesis of small organic molecules in a mixture of simple gases that is placed in a thermal gradient by heating (left) and cooling (right) the mixture at the same time, a mixture that is also subject to electrical discharges]]

The classic 1952 [[Miller–Urey experiment]] and similar research demonstrated that most amino acids, the chemical constituents of the [[protein]]s used in all living organisms, can be synthesized from [[inorganic compound]]s under conditions intended to replicate those of the [[History of Earth|early Earth]]. Scientists have proposed various external sources of energy that may have triggered these reactions, including [[lightning]] and [[radiation]]. Other approaches ("metabolism-first" hypotheses) focus on understanding how [[catalysis]] in chemical systems on the early Earth might have provided the [[Precursor (chemistry)|precursor molecules]] necessary for self-replication.<ref name="Ralser 2014">{{cite journal |last1= Keller |first1= Markus A. |last2= Turchyn |first2= Alexandra V. |last3= Ralser |first3= Markus |date= 25 March 2014 |title= Non‐enzymatic glycolysis and pentose phosphate pathway‐like reactions in a plausible Archean ocean |journal= [[Molecular Systems Biology]] |volume= 10 |issue= 725 |page= 725 |doi= 10.1002/msb.20145228 |pmc= 4023395 |pmid= 24771084}}</ref>

The NASA strategy on abiogenesis states that it is necessary to identify interactions, intermediary structures and functions, energy sources, and environmental factors that contributed to the diversity, selection, and replication of evolvable macromolecular systems. Emphasis must continue to map the chemical landscape of potential primordial informational polymers. The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection likely was a critical step in the emergence of prebiotic chemical evolution.

美国宇航局的自然发生战略指出，有必要确定相互作用、中间结构和功能、能源和环境因素，这些因素促成了可进化大分子系统的多样性、选择和复制。重点必须继续描绘潜在的原始信息聚合物的化学景观。聚合物的出现，可以复制，存储遗传信息，并显示特性受选择可能是一个关键的步骤，在出现前生物化学进化。

The alternative [[panspermia hypothesis]]<ref name="USRA-2010">{{cite conference|last=Rampelotto|first=Pabulo Henrique|date=26 April 2010|title=Panspermia: A Promising Field of Research|url=http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5224.pdf|url-status=live|conference=Astrobiology Science Conference 2010|location=Houston, TX|publisher=[[Lunar and Planetary Institute]]|page=5224|bibcode=2010LPICo1538.5224R|archiveurl=https://web.archive.org/web/20160327005016/http://www.lpi.usra.edu//meetings/abscicon2010/pdf/5224.pdf|archivedate=27 March 2016|accessdate=2014-12-03|conference-url=http://www.lpi.usra.edu/meetings/abscicon2010/}} Conference held at League City, TX</ref> speculates that [[Microorganism|microscopic life]] arose outside Earth by unknown mechanisms, and spread to the early Earth on [[space dust]]<ref name="ARX-20171106">{{cite journal |last= Berera |first= Arjun |title= Space dust collisions as a planetary escape mechanism |journal= Astrobiology |date= 6 November 2017 |arxiv= 1711.01895 |bibcode= 2017AsBio..17.1274B |doi= 10.1089/ast.2017.1662 |pmid= 29148823 |volume= 17 |issue= 12 |pages= 1274–1282|s2cid= 126012488 }}</ref> and [[meteoroid]]s.<ref name="SA-20180110">{{cite journal|last1=Chan|first1=Queenie H.S.|date=10 January 2018|title=Organic matter in extraterrestrial water-bearing salt crystals|journal=[[Science Advances]]|volume=4|page=eaao3521|bibcode=2018SciA....4O3521C|doi=10.1126/sciadv.aao3521|pmc=5770164|pmid=29349297|number=1, eaao3521}}</ref> It is known that complex [[List of interstellar and circumstellar molecules|organic molecules]] occur in the [[Solar System]] and in [[interstellar space]], and these molecules may have provided [[Precursor (chemistry)|starting material]] for the development of life on Earth.<ref name="Ehrenfreund2010" /><ref name="Science 2015">{{cite news|url=http://news.sciencemag.org/chemistry/2015/04/organic-molecules-found-circling-nearby-star?rss=1|title=Organic molecules found circling nearby star|last=Perkins|first=Sid|date=8 April 2015|work=[[Science (journal)|Science]]|accessdate=2015-06-02|publisher=[[American Association for the Advancement of Science]]|location=Washington, DC|type=News}}</ref><ref>{{cite news|url=http://www.rsc.org/chemistryworld/2015/04/meteorites-may-have-delivered-chemicals-started-life-earth|title=Chemicals formed on meteorites may have started life on Earth|last=King|first=Anthony|date=14 April 2015|work=[[Chemistry World]]|accessdate=2015-04-17|archiveurl=https://web.archive.org/web/20150417142723/http://www.rsc.org/chemistryworld/2015/04/meteorites-may-have-delivered-chemicals-started-life-earth|archivedate=17 April 2015|url-status=live|publisher=[[Royal Society of Chemistry]]|location=London|type=News}}</ref><ref>{{cite journal|last1=Saladino|first1=Raffaele|last2=Carota|first2=Eleonora|last3=Botta|first3=Giorgia|last4=Kapralov|first4=Mikhail|last5=Timoshenko|first5=Gennady N.|last6=Rozanov|first6=Alexei Y.|last7=Krasavin|first7=Eugene|last8=Di Mauro|first8=Ernesto|display-authors=3|date=13 April 2015|title=Meteorite-catalyzed syntheses of nucleosides and of other prebiotic compounds from formamide under proton irradiation|journal=[[Proceedings of the National Academy of Sciences of the United States of America|Proc. Natl. Acad. Sci. U.S.A.]]|volume=112|issue=21|pages=E2746–E2755|bibcode=2015PNAS..112E2746S|doi=10.1073/pnas.1422225112|pmc=4450408|pmid=25870268}}</ref>

Similarly, it was realized early on that life requires a loss of entropy, or disorder, when molecules organize themselves into living matter. This Second Law of thermodynamics needs to be considered when self-organization of matter to higher complexity happens. Because living organisms are machines, the Second Law applies to life as well.

同样，人们很早就意识到，当分子组织成活的物质时，生命需要失去熵，或无序。当物质变得更加复杂的时候，我们需要考虑这种热力学第二定律自我组织。因为生命有机体是机器，第二定律同样适用于生命。

Earth remains the only place in the [[universe]] known to harbour life,<ref name="NASA-1990">{{cite web |url= https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900013148.pdf |title= Extraterrestrial Life in the Universe |last= Graham |first= Robert W. |date= February 1990 |place= [[Glenn Research Center|Lewis Research Center]], Cleveland, Ohio |publisher= [[NASA]] |type= NASA Technical Memorandum 102363 |accessdate= 2015-06-02 |url-status= live |archiveurl= https://web.archive.org/web/20140903100534/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900013148.pdf |archivedate= 3 September 2014}}</ref><ref>{{harvnb|Altermann|2009|p=xvii}}</ref> and [[Earliest known life forms|fossil evidence from the Earth]] informs most studies of abiogenesis. The [[age of the Earth]] is 4.54 Gy (Giga or billion year);<ref name="USGS1997">{{cite web |url= http://pubs.usgs.gov/gip/geotime/age.html |title= Age of the Earth |date= 9 July 2007 |publisher= [[United States Geological Survey]] |accessdate= 2006-01-10 |url-status= live |archiveurl= https://web.archive.org/web/20051223072700/http://pubs.usgs.gov/gip/geotime/age.html |archivedate= 23 December 2005}}</ref><ref>{{harvnb|Dalrymple|2001|pp= 205–221}}</ref><ref>{{cite journal |last1= Manhesa |first1= Gérard |last2= Allègre |first2= Claude J. |authorlink2= Claude Allègre |last3= Dupréa |first3= Bernard |last4= Hamelin |first4= Bruno |date= May 1980 |title= Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics |journal= [[Earth and Planetary Science Letters]] |volume= 47 |issue= 3 |pages= 370–382 |bibcode= 1980E&PSL..47..370M |doi= 10.1016/0012-821X(80)90024-2 }}</ref> the earliest undisputed evidence of life on Earth dates from at least 3.5 Gya (Gy ago),<ref name="Origin1">{{cite journal |last1= Schopf |first1= J. William |authorlink1= J. William Schopf |last2= Kudryavtsev |first2= Anatoliy B. |last3= Czaja |first3= Andrew D. |last4= Tripathi |first4= Abhishek B. |date= 5 October 2007 |title= Evidence of Archean life: Stromatolites and microfossils |journal= [[Precambrian Research]] |volume= 158 |pages= 141–155 |issue= 3–4 |doi= 10.1016/j.precamres.2007.04.009 |bibcode= 2007PreR..158..141S }}</ref><ref name="Origin2">{{cite journal |last= Schopf |first= J. William |date= 29 June 2006 |title= Fossil evidence of Archaean life |journal= [[Philosophical Transactions of the Royal Society B]] |volume= 361 |issue= 1470 |pages= 869–885 |doi= 10.1098/rstb.2006.1834 |pmid= 16754604 |pmc=1578735}}</ref><ref name="RavenJohnson2002">{{harvnb|Raven|Johnson|2002|p=68}}</ref> and possibly as early as the [[Eoarchean]] Era (3.6-4.0 Gya). In 2017 scientists found possible evidence of early life [[Evolutionary history of life#Colonization of land|on land]] in 3.48 Gyo (Gy old) [[geyserite]] and other related mineral deposits (often found around [[hot spring]]s and [[geyser]]s) uncovered in the [[Pilbara Craton]] of [[Western Australia]].<ref name="PO-20170509">{{cite news |author= Staff |title= Oldest evidence of life on land found in 3.48-billion-year-old Australian rocks |url= https://phys.org/news/2017-05-oldest-evidence-life-billion-year-old-australian.html |date= 9 May 2017 |work= [[Phys.org]] |accessdate= 13 May 2017 |url-status= live |archiveurl= https://web.archive.org/web/20170510013721/https://phys.org/news/2017-05-oldest-evidence-life-billion-year-old-australian.html |archivedate= 10 May 2017}}</ref><ref name="NC-20170509">{{cite journal |last1= Djokic |first1= Tara |last2= Van Kranendonk |first2= Martin J. |last3= Campbell |first3= Kathleen A. |last4= Walter |first4= Malcolm R. |last5= Ward |first5= Colin R. |title= Earliest signs of life on land preserved in ca. 3.5 Gao hot spring deposits |date= 9 May 2017 |journal= [[Nature Communications]] |doi= 10.1038/ncomms15263 |pmid= 28486437 |pmc= 5436104 |volume= 8 |page= 15263 |bibcode= 2017NatCo...815263D}}</ref><ref name="PNAS-2017">{{cite journal |last1= Schopf |first1= J. William |last2= Kitajima |first2= Kouki |last3= Spicuzza |first3= Michael J. |last4= Kudryavtsev |first4= Anatolly B. |last5= Valley |first5= John W. |title= SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions |date= 2017 |journal= [[Proceedings of the National Academy of Sciences of the United States of America|PNAS]] |doi= 10.1073/pnas.1718063115 |pmid= 29255053 |pmc= 5776830 |volume= 115 |issue= 1 |pages= 53–58|bibcode= 2018PNAS..115...53S }}</ref><ref name="WU-20171218">{{cite web |last= Tyrell |first= Kelly April |title= Oldest fossils ever found show life on Earth began before 3.5 billion years ago |url= https://news.wisc.edu/oldest-fossils-ever-found-show-life-on-earth-began-before-3-5-billion-years-ago/ |date= 18 December 2017 |work= [[University of Wisconsin-Madison]] |accessdate= 18 December 2017 }}</ref> However, a number of discoveries suggest that life may have appeared on Earth even earlier. {{As of | 2017}}, [[Micropaleontology#Microfossils|microfossils]] (fossilised [[microorganism]]s) within [[Hydrothermal vent|hydrothermal-vent precipitates]] dated 3.77 to 4.28 Gya in rocks in [[Quebec]] may harbour the oldest record of life on Earth, suggesting life started soon after [[Origin of water on Earth#Water in the development of Earth|ocean formation 4.4 Gya]] during the [[Hadean]] [[Geologic time scale|Eon]].<ref name="NAT-20170301">{{cite journal |last1= Dodd |first1= Matthew S. |last2= Papineau |first2= Dominic |last3= Grenne |first3= Tor |last4= Slack |first4= John F. |last5= Rittner |first5= Martin |last6= Pirajno |first6= Franco |last7= O'Neil |first7= Jonathan |last8= Little |first8= Crispin T.S. |title= Evidence for early life in Earth's oldest hydrothermal vent precipitates |url= http://eprints.whiterose.ac.uk/112179/ |journal= [[Nature (journal)|Nature]] |date= 1 March 2017 |volume= 543 |issue= 7643 |pages= 60–64 |doi= 10.1038/nature21377 |pmid= 28252057 |accessdate= 2 March 2017 |bibcode= 2017Natur.543...60D |url-status= live |archiveurl= https://web.archive.org/web/20170908201821/http://eprints.whiterose.ac.uk/112179/ |archivedate= 8 September 2017|doi-access= free }}</ref><ref name="NYT-20170301">{{cite news |last= Zimmer |first= Carl |authorlink= Carl Zimmer |title= Scientists Say Canadian Bacteria Fossils May Be Earth's Oldest |url= https://www.nytimes.com/2017/03/01/science/earths-oldest-bacteria-fossils.html |date= 1 March 2017 |work= [[The New York Times]] |accessdate= 2 March 2017 |url-status= live |archiveurl= https://web.archive.org/web/20170302042424/https://www.nytimes.com/2017/03/01/science/earths-oldest-bacteria-fossils.html |archivedate= 2 March 2017}}</ref><ref name="BBC-20170301">{{Cite news |last= Ghosh |first= Pallab |title= Earliest evidence of life on Earth found |url= https://www.bbc.co.uk/news/science-environment-39117523 |publisher= [[BBC News]] |date= 1 March 2017 |accessdate= 2 March 2017 |url-status= live |archiveurl= https://web.archive.org/web/20170302002134/http://www.bbc.co.uk/news/science-environment-39117523 |archivedate= 2 March 2017|work= BBC News }}</ref><ref name="4.3b oldest">{{cite news |last1= Dunham |first1= Will |title= Canadian bacteria-like fossils called oldest evidence of life |url= http://ca.reuters.com/article/topNews/idCAKBN16858B?sp=true |date= 1 March 2017 |agency= [[Reuters]] |accessdate= 1 March 2017 |url-status= live |archiveurl= https://web.archive.org/web/20170302114728/http://ca.reuters.com/article/topNews/idCAKBN16858B?sp=true |archivedate= 2 March 2017}}</ref><ref>{{cite news|title=Researchers uncover 'direct evidence' of life on Earth 4 billion years ago|url= http://dw.com/p/2YUnT|accessdate= 5 March 2017|publisher= Deutsche Welle}}</ref>

Bernal said on the Miller–Urey experiment that <blockquote>it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy.</blockquote>

伯纳尔在 Miller-Urey 的实验中说，仅仅解释这些分子的形成是不够的，必要的是对这些分子的起源进行物理化学解释，这表明存在合适的自由能源和自由能汇。</blockquote >

The NASA strategy on abiogenesis states that it is necessary to identify interactions, intermediary structures and functions, energy sources, and environmental factors that contributed to the diversity, selection, and replication of evolvable macromolecular systems.<ref name="NASA strategy 2015">{{cite web|url=https://nai.nasa.gov/media/medialibrary/2015/10/NASA_Astrobiology_Strategy_2015_151008.pdf|title=NASA Astrobiology Strategy|year=2015|work=NASA|url-status=dead|archiveurl=https://web.archive.org/web/20161222190306/https://nai.nasa.gov/media/medialibrary/2015/10/NASA_Astrobiology_Strategy_2015_151008.pdf|archivedate=22 December 2016|access-date=24 September 2017}}</ref> Emphasis must continue to map the chemical landscape of potential primordial informational [[polymers]]. The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection likely was a critical step in the [[emergence]] of prebiotic chemical evolution.<ref name="NASA strategy 2015"/>

Multiple sources of energy were available for chemical reactions on the early Earth. For example, heat (such as from geothermal processes) is a standard energy source for chemistry. Other examples include sunlight and electrical discharges (lightning), among others.

早期地球上有多种能源用于化学反应。例如，热(如来自地热过程)是标准的化学能源。其他例子包括阳光和闪电等。

== Thermodynamics, self-organization, and information: Physics ==

Computer simulations also suggest that cavitation in primordial water reservoirs such as breaking sea waves, streams and oceans can potentially lead to the synthesis of biogenic compounds.

计算机模拟还表明，原始水库中的空化现象，如破碎的海浪、溪流和海洋，可能导致生物化合物的合成。

===Thermodynamics principles: Energy and entropy===

Unfavourable reactions can also be driven by highly favourable ones, as in the case of iron-sulfur chemistry. For example, this was probably important for carbon fixation (the conversion of carbon from its inorganic form to an organic one).{{efn|The reactions are:

不利的反应也可能是由高度有利的反应引起的，如铁硫化学反应。例如，这可能对固碳(碳从无机形态转化为有机形态)很重要。{{ efn | 反应如下:

In antiquity it was commonly thought, for instance by Empedocles and Aristotle, that the life of the individuals of some species, and more generally, life itself, could start with high temperature, i.e. implicitly by thermal cycling.<ref>{{cite book|title=In the beginning: Some Greek views on the origins of life and the early state of man |year= 1957|last1= Guthrie|first1= W. K. C.|publisher=Methuen, London}}</ref>

FeS + H2S → FeS2 + 2H+ + 2e−

FeS + H2S → FeS2 + 2H+ + 2e−

FeS + H2S + CO2 → FeS2 + HCOOH}} Carbon fixation via iron-sulfur chemistry is highly favourable, and occurs at neutral pH and 100C. Iron-sulfur surfaces, which are abundant near hydrothermal vents, are also capable of producing small amounts of amino acids and other biological metabolites. Hermann Haken has pointed out that different physical systems can be treated in a similar way. He gives as examples of self-organization several types of lasers, instabilities in fluid dynamics, including convection, and chemical and biochemical oscillations. In his preface he mentions the origin of life, but only in general terms:

FeS + h 2 s + CO 2 → FeS 2 + HCOOH }铁硫化学固碳效果较好，发生在中性 pH 和100C 条件下。铁硫表面在热液喷口附近大量存在，也能产生少量的氨基酸和其他生物代谢物。赫尔曼 · 哈肯指出，不同的物理系统可以用相似的方式来处理。他列举了几种类型的激光器，包括对流、化学和生物化学振荡在内的流体动力学的不稳定性，作为自我组织的例子。在他的序言中，他提到了生命的起源，但仅仅是一般性的措辞:

Similarly, it was realized early on that life requires a loss of [[entropy]], or disorder, when molecules organize themselves into living matter. This [[Second law of thermodynamics|Second Law of thermodynamics]] needs to be considered when self-organization of matter to higher complexity happens. Because living organisms are machines,<ref>{{cite book| last1 = Simon| first1 = Michael A. | year = 1971| title = The Matter of Life | edition = 1| location = New Haven and London| publisher = Yale University Press}}</ref> the Second Law applies to life as well.

<blockquote>

< 我们的目标是什么 >

====Obtaining free energy ====

The spontaneous formation of well organized structures out of germs or even out of chaos is one of the most fascinating phenomena and most challenging problems scientists are confronted with. Such phenomena are an experience of our daily life when we observe the growth of plants and animals. Thinking of much larger time scales, scientists are led into the problems of evolution, and, ultimately, of the origin of living matter. When we try to explain or understand in some sense these extremely complex biological phenomena it is a natural question, whether processes of self-organization may be found in much simpler systems of the unanimated world.

从细菌甚至混沌中自发形成组织良好的结构是科学家面临的最令人着迷的现象和最具挑战性的问题之一。当我们观察动植物的生长时，这种现象就是我们日常生活的一种体验。考虑到更大的时间尺度，科学家们被引导到进化的问题上，最终，是生命物质的起源。当我们试图在某种意义上解释或理解这些极其复杂的生物现象时，这是一个自然的问题，自我组织的过程是否可以在一致世界中更简单的系统中找到。

Bernal said on the Miller–Urey experiment that <blockquote>it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy.<ref>{{harvnb|Bernal|1967|p=143}}</ref></blockquote>

In recent years it has become more and more evident that there exists numerous examples in physical and chemical systems where well organized spatial, temporal, or spatio-temporal structures arise out of chaotic states. Furthermore, as in living organisms, the functioning of these systems can be maintained only by a flux of energy (and matter) through them. In contrast to man-made machines, which are devised to exhibit special structures and functionings, these structures develop spontaneously—they are selforganizing. ...

近年来，越来越明显的是，在物理和化学系统中存在着许多由混沌状态产生的组织良好的空间、时间或时空结构的例子。此外，正如在活的有机体中一样，这些系统的功能只能由通过它们的能量(和物质)流来维持。与人造机器不同的是，人造机器是为了展示特殊的结构和功能而设计的，这些结构是自发发展的ーー它们是自组织的。...

Multiple sources of energy were available for chemical reactions on the early Earth. For example, heat (such as from [[geothermal energy|geothermal]] processes) is a standard energy source for chemistry. Other examples include sunlight and electrical discharges (lightning), among others.<ref name="Follmann2009" /> In fact, lightning is a plausible energy source for the origin of life, given that just in the tropics lightning strikes about 100 million times a year.<ref>{{Cite journal|last1=Gora|first1=Evan M.|last2=Burchfield|first2=Jeffrey C.|last3=Muller‐Landau|first3=Helene C.|last4=Bitzer|first4=Phillip M.|last5=Yanoviak|first5=Stephen P.|title=Pantropical geography of lightning-caused disturbance and its implications for tropical forests|journal=Global Change Biology|year=2020|language=en|volume=n/a|issue=n/a|pages=5017–5026|doi=10.1111/gcb.15227|pmid=32564481|bibcode=2020GCBio..26.5017G|issn=1365-2486}}</ref>

</blockquote>

</blockquote >

Computer simulations also suggest that [[cavitation]] in primordial water reservoirs such as breaking sea waves, streams and oceans can potentially lead to the synthesis of biogenic compounds.<ref>{{cite journal|doi=10.1021/acscentsci.7b00325|pmid= 28979946|pmc= 5620973|title= Cavitation-Induced Synthesis of Biogenic Molecules on Primordial Earth|journal= ACS Central Science|volume= 3|issue= 9|pages= 1041–1049|year= 2017|last1= Kalson|first1= Natan-Haim|last2= Furman|first2= David|last3= Zeiri|first3= Yehuda}}</ref>

This theory postulates that the hallmark of the origin and evolution of life is the microscopic dissipative structuring of organic pigments and their proliferation over the entire Earth surface.

这个理论假定生命起源和进化的标志是有机色素的微观耗散结构及其在整个地球表面的扩散。

Unfavourable reactions can also be driven by highly favourable ones, as in the case of iron-sulfur chemistry. For example, this was probably important for [[carbon fixation]] (the conversion of carbon from its inorganic form to an organic one).{{efn|The reactions are:

:FeS + H2S → FeS2 + 2H+ + 2e−

:FeS + H2S + CO2 → FeS2 + HCOOH}} Carbon fixation via iron-sulfur chemistry is highly favourable, and occurs at neutral pH and 100C. Iron-sulfur surfaces, which are abundant near hydrothermal vents, are also capable of producing small amounts of amino acids and other biological metabolites.<ref name="Follmann2009" />

Ilya Prigogine 1977cThe 19th-century physicist Ludwig Boltzmann first recognized that the struggle for existence of living organisms was neither over raw material nor energy, but instead had to do with entropy production derived from the conversion of the solar spectrum into heat by these systems. Boltzmann thus realized that living systems, like all irreversible processes, were dependent on the dissipation of a generalized chemical potential for their existence. In his book "What is Life", the 20th-century physicist Erwin Schrödinger emphasized the importance of Boltzmann's deep insight into the irreversible thermodynamic nature of living systems, suggesting that this was the physics and chemistry behind the origin and evolution of life.

1977年19世纪的物理学家路德维希·玻尔兹曼第一次认识到生命有机体的生存斗争既不是为了原材料也不是为了能源，而是为了通过这些系统将太阳光谱转化为热量而产生的产生熵。玻尔兹曼因此认识到，生命系统，像所有不可逆过程一样，依赖于广义化学势的耗散来维持其存在。在他的著作《什么是生命》中，这位20世纪的物理学家强调了 Boltzmann 对生命系统不可逆热力学性质的深刻洞察的重要性，他认为这是生命起源和进化背后的物理学和化学埃尔温·薛定谔。

===Self-organization===

However, irreversible processes, and much less living systems, could not be conveniently analyzed under this perspective until Lars Onsager, and later Ilya Prigogine, developed an elegant mathematical formalism for treating the "self-organization" of material under a generalized chemical potential. This formalism became known as Classical Irreversible Thermodynamics and Prigogine was awarded the Nobel Prize in Chemistry in 1977 "for his contributions to non-equilibrium thermodynamics, particularly the theory of dissipative structures". The analysis by Prigogine showed that if a system were left to evolve under an imposed external potential, material could spontaneously organize (lower its entropy) forming what he called "dissipative structures" which would increase the dissipation of the externally imposed potential (augment the global entropy production). Non-equilibrium thermodynamics has since been successfully applied to the analysis of living systems, from the biochemical production of ATP to optimizing bacterial metabolic pathways to complete ecosystems.

然而，不可逆过程，以及更少的生命系统，不能在这种观点下方便地分析，直到 Lars Onsager，和后来 Ilya Prigogine，发展了一种优雅的数学形式，在广义化学势下处理材料的“自我组织”。这种形式主义被称为古典不可逆热力学，普里高金因为“对非平衡态热力学，特别是耗散结构理论的贡献”而在1977年被授予诺贝尔化学奖。Prigogine 的分析表明，如果一个系统在强加的外部势能下进化，材料可以自发组织(降低其熵)形成他所谓的“耗散结构” ，这将增加外部势能的耗散(增加全球产生熵)。非平衡态热力学已经成功地应用于生命系统的分析，从 ATP 的生化产物到优化细菌代谢途径，最终完成生态系统。

[[File:Hermann Haken, Pour le Merite 2014.jpg|thumb|upright|Hermann Haken]]

The discipline of synergetics studies self-organization in physical systems. In his book ''[[Synergetics (Haken)|Synergetics]]''<ref>{{cite book |last1 = Haken| first1= Hermann | title=Synergetics. An Introduction. |year=1978 | publisher=Springer | location= Berlin }}</ref> [[Hermann Haken]] has pointed out that different physical systems can be treated in a similar way. He gives as examples of self-organization several types of lasers, instabilities in fluid dynamics, including convection, and chemical and biochemical oscillations. In his preface he mentions the origin of life, but only in general terms:

<blockquote>

The spontaneous formation of well organized structures out of germs or even out of chaos is one of the most fascinating phenomena and most challenging problems scientists are confronted with. Such phenomena are an experience of our daily life when we observe the growth of plants and animals. Thinking of much larger time scales, scientists are led into the problems of evolution, and, ultimately, of the origin of living matter. When we try to explain or understand in some sense these extremely complex biological phenomena it is a natural question, whether processes of self-organization may be found in much simpler systems of the unanimated world.

When discussing the origin of life, a definition of life itself is fundamental. The definition is somewhat disagreed upon (although follows the same basic principles) because different biology textbooks define life differently. James Gould:

当讨论生命的起源时，对生命本身的定义是最基本的。由于不同的生物学教科书对生命的定义不同，所以对生命的定义存在一些分歧(尽管它们遵循的是同样的基本原则)。詹姆斯 · 古尔德:

<blockquote>

< 我们的目标是什么 >

In recent years it has become more and more evident that there exists numerous examples in physical and chemical systems where well organized spatial, temporal, or spatio-temporal structures arise out of chaotic states. Furthermore, as in living organisms, the functioning of these systems can be maintained only by a flux of energy (and matter) through them. In contrast to man-made machines, which are devised to exhibit special structures and functionings, these structures develop spontaneously—they are ''selforganizing''. ...<ref>{{cite book |last1 = Haken| first1= Hermann | title=Synergetics. An Introduction. |year=1978 | publisher=Springer }}</ref>

Most dictionaries define life as the property that distinguishes the living from the dead, and define dead as being deprived of life. These singularly circular and unsatisfactory definitions give us no clue to what we have in common with protozoans and plants. </blockquote>

大多数字典将生命定义为区分生者和死者的属性，将死者定义为被剥夺了生命。这些奇怪的循环和令人不满意的定义给我们提供不了任何线索，我们与原生动物和植物有什么共同点。</blockquote >

</blockquote>

whereas according to Neil Campbell and Jane Reece <blockquote>The phenomenon we call life defies a simple, one-sentence definition.</blockquote>

然而，根据尼尔 · 坎贝尔和简 · 里斯的研究，我们称之为生活的现象违背了一个简单的、一句话的定义

====Multiple dissipative structures====

This difference can also be found in books on the origin of life. John Casti gives a single sentence:

这种差异也可以在关于生命起源的书籍中找到。约翰 · 卡斯蒂只说了一句话:

This theory postulates that the hallmark of the origin and evolution of life is the microscopic dissipative structuring of [[Biological pigment|organic pigments]] and their proliferation over the entire Earth surface.<ref name="Michaelian, K. 2017" /> Present day life augments the entropy production of Earth in its solar environment by dissipating [[ultraviolet]] and [[Visible spectrum|visible]] [[photon]]s into heat through organic pigments in water. This heat then catalyzes a host of secondary dissipative processes such as the [[water cycle]], [[Ocean current|ocean]] and [[wind]] currents, [[Tropical cyclone|hurricanes]], etc.<ref name="Michaelian, K. 2011"/><ref name="HESS Opinions 'Biological catalysis">{{cite journal |doi=10.5194/hess-16-2629-2012 |title=HESS Opinions 'Biological catalysis of the hydrological cycle: Life's thermodynamic function' |journal=Hydrology and Earth System Sciences |volume=16 |issue=8 |pages=2629–2645 |year=2012 |last1=Michaelian |first1=K |bibcode=2012HESS...16.2629M |arxiv= 0907.0040 }}</ref>

<blockquote>By more or general consensus nowadays, an entity is considered to be "alive" if it has the capacity to carry out three basic functional activities: metabolism, self-repair, and replication.

如今，更多或更广泛的共识认为，如果一个实体有能力进行三项基本功能活动: 新陈代谢、自我修复和复制，那么它就是“活的”。

</blockquote> Dirk Schulze-Makuch and Louis Irwin spend in contrast the whole first chapter of their book on this subject.

德克 · 舒尔茨-马库奇和路易斯 · 欧文在这个主题上花费了他们书中整个第一章的篇幅。

==== Selforganization by dissipative structures====

[[File:Ilya Prigogine 1977c.jpg|thumb|upright|Ilya Prigogine 1977c]]The 19th-century physicist [[Ludwig Boltzmann]] first recognized that the struggle for existence of living organisms was neither over raw material nor [[energy]], but instead had to do with [[entropy production]] derived from the conversion of the solar [[spectrum]] into [[heat]] by these systems.<ref>Boltzmann, L. (1886) The Second Law of Thermodynamics, in: Ludwig Boltzmann: Theoretical physics and Selected writings, edited by: McGinness, B., D. Reidel, Dordrecht, The Netherlands, 1974.</ref> Boltzmann thus realized that living systems, like all [[Reversible process (thermodynamics)|irreversible processes]], were dependent on the [[dissipation]] of a generalized chemical potential for their existence. In his book "What is Life", the 20th-century physicist [[Erwin Schrödinger]]<ref>Schrödinger, Erwin (1944) What is Life? The Physical Aspect of the Living Cell. Cambridge University Press</ref> emphasized the importance of Boltzmann's deep insight into the irreversible thermodynamic nature of living systems, suggesting that this was the physics and chemistry behind the origin and evolution of life.

Citric acid cycle

三羧酸循环

However, irreversible processes, and much less living systems, could not be conveniently analyzed under this perspective until [[Lars Onsager]],<ref>Onsager, L. (1931) Reciprocal Relations in Irreversible Processes I and II, ''Phys. Rev.'' 37, 405; 38, 2265 (1931)</ref> and later Ilya [[Ilya Prigogine|Prigogine]],<ref>Prigogine, I. (1967) An Introduction to the Thermodynamics of Irreversible Processes, Wiley, New York</ref> developed an elegant mathematical formalism for treating the "self-organization" of material under a generalized chemical potential. This formalism became known as Classical Irreversible Thermodynamics and Prigogine was awarded the [[Nobel Prize in Chemistry]] in 1977 "for his contributions to [[non-equilibrium thermodynamics]], particularly the theory of [[Dissipative system|dissipative structures]]". The analysis by Prigogine showed that if a [[system]] were left to evolve under an imposed external potential, material could spontaneously organize (lower its [[entropy]]) forming what he called "dissipative structures" which would increase the dissipation of the externally imposed potential (augment the global entropy production). Non-equilibrium thermodynamics has since been successfully applied to the analysis of living systems, from the biochemical production of [[Adenosine triphosphate|ATP]]<ref>{{cite journal | last1 = Dewar | first1 = R | last2 = Juretić | first2 = D. | last3 = Županović | first3 = P. | year = 2006 | title = The functional design of the rotary enzyme ATP synthase is consistent with maximum entropy production | journal = Chem. Phys. Lett. | volume = 430 | issue = 1| pages = 177–182 | doi=10.1016/j.cplett.2006.08.095| bibcode = 2006CPL...430..177D }}</ref> to optimizing bacterial metabolic pathways<ref>Unrean, P., Srienc, F. (2011) Metabolic networks evolve towards states of maximum entropy production, Metabolic Engineering 13, 666–673.</ref> to complete ecosystems.<ref>Zotin, A.I. (1984) "Bioenergetic trends of evolutionary progress of organisms", in: ''Thermodynamics and regulation of biological processes'' Lamprecht, I. and Zotin, A.I. (eds.), De Gruyter, Berlin, pp. 451–458.</ref><ref>{{cite journal | last1 = Schneider | first1 = E.D. | last2 = Kay | first2 = J.J. | year = 1994 | title = Life as a Manifestation of the Second Law of Thermodynamics | journal = Mathematical and Computer Modelling | volume = 19 | issue = 6–8| pages = 25–48 | doi=10.1016/0895-7177(94)90188-0| citeseerx = 10.1.1.36.8381 }}</ref><ref>{{cite journal | last1 = Michaelian | first1 = K. | year = 2005 | title = Thermodynamic stability of ecosystems | journal = Journal of Theoretical Biology | volume = 237 | issue = 3| pages = 323–335 | bibcode = 2004APS..MAR.P9015M | doi=10.1016/j.jtbi.2005.04.019| pmid = 15978624 }}</ref>

Overall diagram of the chemical reactions of metabolism, in which the citric acid cycle can be recognized as the circle just below the middle of the figure Albert Lehninger has stated around 1970 that fermentation, including glycolysis, is a suitable primitive energy source for the origin of life.

在新陈代谢的化学反应的总体图表中，三羧酸循环可以被认为是 Albert Lehninger 在1970年前后所说的图形中间的圆圈，发酵，包括糖酵解，是生命起源的一个合适的原始能源。

<blockquote> Since living organisms probably first arose in an atmosphere lacking oxygen, anaerobic fermentation is the simplest and most primitive type of biological mechanism for obtaining energy from nutrient molecules. </blockquote>

由于生物体最初可能是在缺氧的大气中产生的，厌氧发酵是从营养分子中获取能量的最简单、最原始的生物机制。</blockquote >

== Current life, the result of abiogenesis: biology==

Fermentation involves glycolysis, which, rather inefficiently, transduces the chemical energy of sugar into the chemical energy of ATP.

发酵过程包括糖酵解，糖酵解将糖的化学能转化为三磷酸腺苷的化学能，效率很低。

===Definition of life===

When discussing the origin of life, a definition of life itself is fundamental. The definition is somewhat disagreed upon (although follows the same basic principles) because different biology textbooks define life differently. James Gould:

<blockquote>

Oxidative phosphorylation

氧化磷酸化

Most dictionaries define ''life'' as the property that distinguishes the living from the dead, and define ''dead'' as being deprived of life. These singularly circular and unsatisfactory definitions give us no clue to what we have in common with protozoans and plants. <ref “Gould”>{{cite book| last1 = Gould | first1 = James L. | last2 = Keeton | first2 = William T. | year = 1996| edition = 6 | title = Biological Science | location= New York | publisher = W.W. Norton }}</ref></blockquote>

Chemiosmotic coupling mitochondrion

线粒体化学渗透偶联

whereas according to Neil Campbell and Jane Reece <blockquote>The phenomenon we call life defies a simple, one-sentence definition.<ref “Campbell”>{{cite book| last1 = Campbell | first1 = Neil A. | last2 = Reece | first2 = Jane B.| year = 2005| edition = 7 | title = Biology | location= Sn Feancisco | publisher = Benjamin }}</ref></blockquote>

As Fermentation had around 1970 been elucidated, whereas the mechanism of oxidative phosphorylation had not and some controversies still existed, fermentation may have looked too complex for investigators of the origin of life at that time. Peter Mitchell's Chemiosmosis is now however generally accepted as correct.

由于发酵在1970年前后已经被阐明，而氧化磷酸化的机制尚未被阐明，而且一些争议仍然存在，发酵在当时对于生命起源的研究者来说可能看起来过于复杂。彼得 · 米切尔的《化学渗透》现在被普遍认为是正确的。

This difference can also be found in books on the origin of life. John Casti gives a single sentence:

<blockquote>By more or general consensus nowadays, an entity is considered to be "alive" if it has the capacity to carry out three basic functional activities: metabolism, self-repair, and replication.

Even Peter Mitchell himself assumed that fermentation preceded chemiosmosis. Chemiosmosis is however ubiquitous in life. A model for the origin of life has been presented in terms of chemiosmosis.

甚至连彼得 · 米切尔自己都认为发酵先于化学反应。然而，化学反应在生活中是无处不在的。本文用化学方法提出了生命起源的模型。

<ref “Casti”>{{cite book| last1 = Casti | first1 = John L. | year = 1989| title = Paradigms lost. Images of man in the mirror of science | location= New York | publisher = Morrow | bibcode = 1989plim.book.....C }}</ref></blockquote> Dirk Schulze-Makuch and Louis Irwin spend in contrast the whole first chapter of their book on this subject.<ref “Schulze-Makuch”>{{cite book| last1 = Schulze-Makuch | first1 = Dirk | last2 = Irwin

| first2 = Louis N. | year = 2018| edition = 3 | title = Life in the Universe. Expectations and Constraints | location= New York | publisher = Springer }}</ref>

Both respiration by mitochondria and photosynthesis in chloroplasts make use of chemiosmosis to generate most of their ATP.

线粒体的呼吸作用和叶绿体的光合作用都利用化学作用来产生大部分的 ATP。

====Fermentation====

[[File:Citric acid cycle.svg|thumb|upright=1.5|left|Citric acid cycle]]

Today the energy source of all life can be linked to photosynthesis, and one speaks of primary production by sunlight. The oxygen used for oxidizing reducing compounds by organisms at hydrothermal vents at the bottom of the ocean is the result of photosynthesis at the Oceans' surface.

今天，所有生命的能量来源都可以与光合作用联系起来，人们谈到初级生产是靠阳光。海底热液喷口的生物用来氧化还原性化合物的氧气是海洋表面光合作用的结果。

[[File:Metabolism diagram.svg|thumb|Overall diagram of the chemical reactions of metabolism, in which the citric acid cycle can be recognized as the circle just below the middle of the figure]] [[Albert L. Lehninger|Albert Lehninger]] has stated around 1970 that fermentation, including glycolysis, is a suitable primitive energy source for the origin of life.<ref “Lehninger”>{{cite book| last1 = Lehninger | first1 = Albert L. | year = 1970| title = Biochemistry. The Molecular Basis of Cell Structure and Function | location= New York | publisher = Worth | page = 313}}</ref>

<blockquote> Since living organisms probably first arose in an atmosphere lacking oxygen, anaerobic fermentation is the simplest and most primitive type of biological mechanism for obtaining energy from nutrient molecules. </blockquote>

Depiction of ATP synthase using the chemiosmotic proton gradient to power ATP synthesis through [[oxidative phosphorylation.]]

用化学渗透质子梯度描述 ATP 合成酶通过[氧化磷酸化]

Fermentation involves glycolysis, which, rather inefficiently, transduces the chemical energy of sugar into the chemical energy of ATP.

Paul Boyer

保罗 · 博耶

The mechanism of ATP synthesis is complex and involves a closed membrane in which the ATP synthase is embedded. The ATP is synthesized by the F1 subunit of ATP synthase by the binding change mechanism discovered by Paul Boyer. The energy required to release formed strongly-bound ATP has its origin in protons that move across the membrane. These protons have been set across the membrane during respiration or photosynthesis.

ATP 合成的机制是复杂的，涉及到一个封闭的膜，其中 ATP 合成酶嵌入。ATP 是由 ATP 合成酶的 F1亚基通过保罗 · 博耶发现的结合变化机制合成的。释放形成强结合 ATP 所需的能量来源于跨膜运动的质子。这些质子是在呼吸作用或光合作用时通过膜传递的。

====Chemiosmosis====

[[File:Oxiphos.png|thumb|left|upright=1.25|Oxidative phosphorylation]]

[[File:Chemiosmotic coupling mitochondrion.gif|thumb|left|upright=1.25|Chemiosmotic coupling mitochondrion]]

ribosome 30S subunit from Thermus thermophilus. Proteins are shown in blue and the single RNA chain in orange.]]

嗜热栖热菌的核糖体30S 亚基。蛋白质以蓝色显示，单链 RNA 以橙色显示。]

The RNA world hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins. It is widely accepted that current life on Earth descends from an RNA world, although RNA-based life may not have been the first life to exist. The structure of the ribosome has been called the "smoking gun," as it showed that the ribosome is a ribozyme, with a central core of RNA and no amino acid side chains within 18 angstroms of the active site where peptide bond formation is catalyzed.

RNA世界学说描述了一个早期的地球，它具有自我复制和催化的 RNA，但没有 DNA 或蛋白质。人们普遍认为，地球上目前的生命起源于 RNA 世界，尽管基于 RNA 的生命可能并不是第一个存在的生命。核糖体的结构被称为“确凿的证据” ，因为它表明核糖体是一种核酶，其核心是 RNA，在催化肽键形成的活性位点的18个角内没有氨基酸侧链。

As [[Fermentation]] had around 1970 been elucidated, whereas the mechanism of oxidative phosphorylation had not and some controversies still existed, fermentation may have looked too complex for investigators of the origin of life at that time. [[Peter D. Mitchell|Peter Mitchell]]'s [[Chemiosmosis]] is now however generally accepted as correct.

The concept of the RNA world was first proposed in 1962 by Alexander Rich, and the term was coined by Walter Gilbert in 1986.

RNA 世界的概念最早由亚历山大 · 里奇在1962年提出，这个术语是由沃尔特 · 吉尔伯特在1986年杜撰的。

Even Peter Mitchell himself assumed that fermentation preceded chemiosmosis. Chemiosmosis is however ubiquitous in life. A model for the origin of life has been presented in terms of chemiosmosis.

In March 2020, astronomer Tomonori Totani presented a statistical approach for explaining how an initial active RNA molecule might have been produced randomly in the universe sometime since the Big Bang.

2020年3月，天文学家 toonori Totani 提出了一个统计方法，用来解释自大爆炸以来宇宙中最初的活跃 RNA 分子是如何随机产生的。

<ref>{{cite journal

| author = Anthonie W.J. Muller

| year = 1995

cladogram demonstrating extreme hyperthermophiles as occur in volcanic hot springs at the base of the phylogenetic tree of life.]]The most commonly accepted location of the root of the tree of life is between a monophyletic domain Bacteria and a clade formed by Archaea and Eukaryota of what is referred to as the "traditional tree of life" based on several molecular studies starting with Carl Woese.

分支图展示了生命系统发生树底部的火山温泉中所发现的极端超高温菌。[英语背诵文选生命之树根的最普遍接受的位置是介于单系域细菌和由古细菌和真核生物形成的分支之间，这种分支基于从卡尔 · 沃斯开始的几项分子研究，被称为“传统生命之树”。

| title = Were the first organisms heat engines? A new model for biogenesis and the early evolution of biological energy conversion

| journal = Progress in Biophysics and Molecular Biology

A very small minority of studies have concluded differently, namely that the root is in the domain Bacteria, either in the phylum Firmicutes or that the phylum Chloroflexi is basal to a clade with Archaea+Eukaryotes and the rest of Bacteria as proposed by Thomas Cavalier-Smith. More recently, Peter Ward has proposed an alternative view which is rooted in abiotic RNA synthesis which becomes enclosed within a capsule and then creates RNA ribozyme replicates. It is proposed that this then bifurcates between Dominion Ribosa (RNA life), and after the loss of ribozymes RNA viruses as Domain Viorea, and Dominion Terroa, which after creating a large cell within a lipid wall, creating DNA the 20 based amino acids and the triplet code, is established as the last universal common ancestor or LUCA, of earlier phylogenic trees.

一小部分研究得出了不同的结论，即根是在细菌的领域，或者是在门厚壁菌，或者是氯化物门是基于一个古细菌 + 真核生物的分支和其余的细菌，如汤玛斯·卡弗利尔-史密斯所提出的。最近，彼得 · 沃德提出了另一种观点，这种观点植根于非生物 RNA 合成，这种合成被包裹在一个胶囊中，然后产生 RNA 核酶复制。有人提出，这然后分岔之间的自治核糖体(RNA 生命) ，并失去核酶 RNA 病毒作为结构域 Viorea，和自治 Terroa，后者创造了一个大细胞内的脂质壁，创造 DNA 的20个基础氨基酸和三重态码，是建立作为最后的普遍共同祖先或卢卡，早期系统发育树。

| volume = 63

| pages=193–231

In 2016, a set of 355 genes likely present in the Last Universal Common Ancestor (LUCA) of all organisms living on Earth was identified. A total of 6.1 million prokaryotic protein coding genes from various phylogenic trees were sequenced, identifying 355 protein clusters from amongst 286,514 protein clusters that were probably common to LUCA. The results

2016年，一组355个基因可能存在于地球上所有生物体的最后共同祖先(LUCA)中。测序了来自不同系统发育树的610万个原核蛋白编码基因，从286514个可能与 LUCA 共有的蛋白质簇中鉴定出355个蛋白质簇。结果

| doi = 10.1016/0079-6107(95)00004-7

<blockquote>. . . depict LUCA as anaerobic, CO2-fixing, H2-dependent with a Wood–Ljungdahl pathway, N2-fixing and thermophilic. LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms. Its cofactors reveal dependence upon transition metals, flavins, S-adenosyl methionine, coenzyme A, ferredoxin, molybdopterin, corrins and selenium. Its genetic code required nucleoside modifications and S-adenosylmethionine-dependent methylations."

< 封锁报价 > 。..表现为缺氧、 CO 2 -fixing，h 2 依赖于 Wood-Ljungdahl 通路，n 2 -fixing 和嗜热。露卡的生化反应充满了 FeS 团簇和自由基反应机制。其辅助因子主要依赖于过渡金属、黄素、 s- 腺苷蛋氨酸、辅酶 a、铁氧还蛋白、钼杂多蛋白、角蛋白和硒。它的遗传密码需要核苷修饰和 s- 腺苷蛋氨酸依赖的甲基化

| pmid = 7542789

</blockquote>The results depict methanogenic clostridia as a basal clade in the 355 phylogenies examined, and suggest that LUCA inhabited an anaerobic hydrothermal vent setting in a geochemically active environment rich in H2, CO2 and iron.

结果显示产甲烷梭状芽胞杆菌在355个系统发育分支中是一个基本分支，提示 LUCA 生活在一个富含 h 2 ，CO 2 和 fe 的地球化学活性环境中的无氧深海热泉中。

| issue = 2

}}</ref><ref>

A study at the University of Düsseldorf created phylogenic trees based upon 6 million genes from bacteria and archaea, and identified 355 protein families that were probably present in the LUCA. They were based upon an anaerobic metabolism fixing carbon dioxide and nitrogen. It suggests that the LUCA evolved in an environment rich in hydrogen, carbon dioxide and iron.

杜塞尔多夫大学的一项研究基于细菌和古生菌的600万个基因创建了系统发育树，并确定了可能存在于 LUCA 中的355个蛋白质家族。它们是基于固定二氧化碳和氮的无氧代谢。这表明露卡是在一个富含氢、二氧化碳和铁的环境中进化的。

{{cite journal

| author = Anthonie W.J. Muller and Dirk Schulze-Makuch

| title = Thermal energy and the origin of life

| journal = Origins of Life and Evolution of Biospheres

Possible precursors for the evolution of protein synthesis include a mechanism to synthesize short peptide cofactors or form a mechanism for the duplication of RNA. It is likely that the ancestral ribosome was composed entirely of RNA, although some roles have since been taken over by proteins. Major remaining questions on this topic include identifying the selective force for the evolution of the ribosome and determining how the genetic code arose.

蛋白质合成进化的可能前体包括合成短肽辅因子的机制或形成 RNA 复制的机制。原始的核糖体可能完全由 RNA 组成，尽管其中一些作用已经被蛋白质所取代。剩下的主要问题包括确定核糖体进化的选择性力量和确定遗传密码是如何产生的。

| volume = 36

| issue = 2

Eugene Koonin said, <blockquote>Despite considerable experimental and theoretical effort, no compelling scenarios currently exist for the origin of replication and translation, the key processes that together comprise the core of biological systems and the apparent pre-requisite of biological evolution. The RNA World concept might offer the best chance for the resolution of this conundrum but so far cannot adequately account for the emergence of an efficient RNA replicase or the translation system. The MWO ["many worlds in one"] version of the cosmological model of eternal inflation could suggest a way out of this conundrum because, in an infinite multiverse with a finite number of distinct macroscopic histories (each repeated an infinite number of times), emergence of even highly complex systems by chance is not just possible but inevitable.</blockquote>

尽管在实验和理论上付出了相当大的努力，但是目前还没有令人信服的复制原点和转化方案，这两个关键过程共同构成了生物系统的核心和生物进化的明显先决条件。RNA 世界的概念可能为解决这一难题提供了最好的机会，但迄今为止还不能充分说明出现了一个有效的 RNA 复制酶或翻译系统。宇宙永恒膨胀的宇宙学模型的 MWO (“多个世界合为一体”)版本可能提供了一条解决这个难题的途径，因为在一个具有有限数量的不同宏观历史的无限多元宇宙中(每个宏观历史重复了无限次) ，偶然出现甚至高度复杂的系统不仅是可能的，而且是不可避免的。</blockquote >

| year=2006

| pages=77–189

| pmid = 16642267

See: Genetic code.

参见: 遗传密码。

| doi =10.1007/s11084-005-9003-4

|bibcode = 2006OLEB...36..177M | s2cid = 22179552

}}</ref>

Hoffmann has shown that an early error-prone translation machinery can be stable against an error catastrophe of the type that had been envisaged as problematical for the origin of life, and was known as "Orgel's paradox".

霍夫曼已经证明，早期容易出错的翻译机器可以稳定地抵御错误灾难，这种灾难被认为是生命起源的问题，被称为“奥格尔悖论”。

Both respiration by mitochondria and photosynthesis in chloroplasts make use of chemiosmosis to generate most of their ATP.

Today the energy source of all life can be linked to photosynthesis, and one speaks of primary production by sunlight. The oxygen used for oxidizing reducing compounds by organisms at hydrothermal vents at the bottom of the ocean is the result of photosynthesis at the Oceans' surface.

Homochirality refers to a geometric uniformity of some materials composed of chiral units. Chiral refers to nonsuperimposable 3D forms that are mirror images of one another, as are left and right hands. Living organisms use molecules that have the same chirality ("handedness"): with almost no exceptions, amino acids are left-handed while nucleotides and sugars are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst, they are formed in a 50/50 mixture of both enantiomers (called a racemic mixture). Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction; asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, statistical fluctuations during racemic synthesis, and spontaneous symmetry breaking.

同手性是指一些由手性单元组成的材料的几何均匀性。手征性是指不可叠加的三维形式，它们是彼此的镜像，就像左手和右手一样。生物体使用的分子具有相同的手性(“手性”) : 几乎没有例外，氨基酸是左手性的，而核苷酸和糖是右手性的。手性分子是可以合成的，但在没有手性来源或手性催化剂的情况下，它们是在两种对映体的50/50混合物(称为外消旋混合物)中形成的。从外消旋起始物质生成非外消旋混合物的已知机制包括: 不对称物理定律，如电弱相互作用; 不对称环境，如圆偏振光、石英晶体或地球自转引起的不对称环境，外消旋合成过程中的统计波动，以及自发对称性破缺。

=====ATP synthase=====

Once established, chirality would be selected for. A small bias (enantiomeric excess) in the population can be amplified into a large one by asymmetric autocatalysis, such as in the Soai reaction. In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other.

一旦确定，将选择手性。通过不对称的自催化反应，例如在 Soai 反应中，人群中的一个小的偏向(对映体过量百分数)可以被放大到一个大的偏向。在不对称自催化反应中，催化剂是一个手性分子，这意味着手性分子正在催化自身的生成。最初的对映体过量百分数，比如偏振光可以产生，然后允许更多的对映异构体战胜其他的。

[[File:ATP-Synthase.svg|thumb|upright|left|Depiction of ATP synthase using the chemiosmotic proton gradient to power ATP synthesis through [[oxidative phosphorylation]].]]

[[File:Paul D. Boyer.jpg|thumb|upright|Paul Boyer]]

Clark has suggested that homochirality may have started in outer space, as the studies of the amino acids on the Murchison meteorite showed that L-alanine is more than twice as frequent as its D form, and L-glutamic acid was more than three times prevalent than its D counterpart. Various chiral crystal surfaces can also act as sites for possible concentration and assembly of chiral monomer units into macromolecules. Compounds found on meteorites suggest that the chirality of life derives from abiogenic synthesis, since amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, the same as found in living organisms.

克拉克提出，同手性可能起源于外太空，因为对默奇森陨石上氨基酸的研究表明，l- 丙氨酸的频率是其 d 型氨基酸的两倍以上，而 l- 谷氨酸的普遍性是其 d 型氨基酸的三倍以上。各种手性晶体表面也可以作为可能的浓缩和手性单体组装成大分子的位点。陨石上发现的化合物表明，生命的手性来自于非生物合成，因为陨石中的氨基酸呈左旋偏向，而糖呈右旋偏向，这与活生物体中发现的情况相同。

The mechanism of ATP synthesis is complex and involves a closed membrane in which the [[ATP synthase]] is embedded. The ATP is synthesized by the F1 subunit of ATP synthase by the [[ATP synthase#Binding model|binding change mechanism]] discovered by [[Paul D. Boyer|Paul Boyer]]. The energy required to release formed strongly-bound ATP has its origin in protons that move across the membrane. These protons have been set across the membrane during respiration or photosynthesis.

====RNA world====

[[File:010 small subunit-1FKA.gif|thumb|upright=1.25|Molecular structure of the [[30S|ribosome 30S subunit]] from ''[[Thermus thermophilus]]''.<ref name="Venki">{{cite journal |last1=Wimberly |first1=Brian T. |last2=Brodersen |first2=Ditlev E. |last3=Clemons |first3=William M. Jr. |last4=Morgan-Warren |first4=Robert J. |last5=Carter |first5=Andrew P. |last6=Vonrhein |first6=Clemens |last7=Hartsch |first7=Thomas |last8=Ramakrishnan |first8=V. |authorlink8=Venkatraman Ramakrishnan |display-authors=3 |date=21 September 2000 |title=Structure of the 30S ribosomal subunit |journal=Nature |volume=407 |issue=6802 |pages=327–339 |doi=10.1038/35030006 |pmid=11014182|bibcode=2000Natur.407..327W |s2cid=4419944 }}</ref> [[Protein]]s are shown in blue and the single [[RNA]] chain in orange.]]

The [[RNA world]] hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins.<ref name="NYT-20140925-CZ">{{cite news |last=Zimmer |first=Carl |date=25 September 2014 |title=A Tiny Emissary From the Ancient Past |url=https://www.nytimes.com/2014/09/25/science/a-tiny-emissary-from-the-ancient-past.html |newspaper=The New York Times |location=New York |accessdate=2014-09-26 |url-status=live |archiveurl=https://web.archive.org/web/20140927022738/http://www.nytimes.com/2014/09/25/science/a-tiny-emissary-from-the-ancient-past.html |archivedate=27 September 2014}}</ref> It is widely accepted that current life on Earth descends from an RNA world,<ref name="RNA">*{{cite journal |last1=Copley |first1=Shelley D. |last2=Smith |first2=Eric |last3=Morowitz |first3=Harold J. |authorlink3=Harold J. Morowitz |date=December 2007 |title=The origin of the RNA world: Co-evolution of genes and metabolism |url=http://tuvalu.santafe.edu/~desmith/PDF_pubs/Copley_BOG.pdf |journal=Bioorganic Chemistry |volume=35 |issue=6 |pages=430–443 |doi=10.1016/j.bioorg.2007.08.001 |pmid=17897696 |accessdate=2015-06-08 |quote=The proposal that life on Earth arose from an RNA world is widely accepted. |url-status=live |archiveurl=https://web.archive.org/web/20130905070129/http://tuvalu.santafe.edu/~desmith/PDF_pubs/Copley_BOG.pdf |archivedate=5 September 2013}}

* {{cite journal |last=Orgel |first=Leslie E. |authorlink=Leslie Orgel |date=April 2003 |title=Some consequences of the RNA world hypothesis |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=2 |pages=211–218 |doi=10.1023/A:1024616317965 |pmid=12967268 |quote=It now seems very likely that our familiar DNA/RNA/protein world was preceded by an RNA world...|bibcode=2003OLEB...33..211O |s2cid=32779859 }}

* {{harvnb|Robertson|Joyce|2012}}: "There is now strong evidence indicating that an RNA World did indeed exist before DNA- and protein-based life."

* {{harvnb|Neveu|Kim|Benner|2013}}: "[The RNA world's existence] has broad support within the community today."</ref><ref name="NYT-20150504">{{cite news |last=Wade |first=Nicholas |authorlink=Nicholas Wade |date=4 May 2015 |title=Making Sense of the Chemistry That Led to Life on Earth |url=https://www.nytimes.com/2015/05/05/science/making-sense-of-the-chemistry-that-led-to-life-on-earth.html |newspaper=The New York Times |location=New York |accessdate=2015-05-10 |url-status=live |archiveurl=https://web.archive.org/web/20170709115606/https://www.nytimes.com/2015/05/05/science/making-sense-of-the-chemistry-that-led-to-life-on-earth.html |archivedate=9 July 2017}}</ref><ref>{{cite journal |last1= Benner|first1=S.A. |last2=Bell |first2=E.A.|last3=Biondi |first3=E. |last4=Brasser |first4=R.|last5=Carell |first5=T. | last6=Kim |first6=H.-J.| last7=Mojzsis |first7=S.J. | last8=Omran |first8=A. |last9=Pasek |first9=M.A. | last10=Trail |first10=D. |date=2020 |title=When Did Life Likely Emerge on Earth in an RNA‐First Process? |journal=ChemSystemsChem |volume=2|issue=2 |doi=10.1002/syst.201900035|doi-access=free }}</ref> although RNA-based life may not have been the first life to exist.<ref name="Robertson2012" /><ref name="Cech2012" /> This conclusion is drawn from many independent lines of evidence, such as the observations that RNA is central to the translation process and that small RNAs can catalyze all of the chemical groups and information transfers required for life.<ref name="Cech2012" /><ref name="Yarus2011">{{cite journal |last=Yarus |first=Michael |date=April 2011 |title=Getting Past the RNA World: The Initial Darwinian Ancestor |journal=Cold Spring Harbor Perspectives in Biology |volume=3 |issue=4 |page=a003590 |doi=10.1101/cshperspect.a003590 |pmc=3062219 |pmid=20719875}}</ref> The structure of the [[ribosome]] has been called the "smoking gun," as it showed that the ribosome is a ribozyme, with a central core of RNA and no amino acid side chains within 18 angstroms of the [[active site]] where peptide bond formation is catalyzed.<ref name="Robertson2012">{{cite journal |last1=Robertson |first1=Michael P. |last2=Joyce |first2=Gerald F. |authorlink2=Gerald Joyce |date=May 2012 |title=The origins of the RNA world |journal=Cold Spring Harbor Perspectives in Biology |volume=4 |issue=5 |page=a003608 |doi=10.1101/cshperspect.a003608 |pmc=3331698 |pmid=20739415 |ref=harv}}</ref><ref>{{cite journal |last1=Fox |first1=George.E. |date=9 June 2010 |title=Origin and evolution of the ribosome |journal=Cold Spring Harbor Perspectives in Biology |volume=2 |issue=9(a003483) |pages=a003483 |doi=10.1101/cshperspect.a003483 |pmid=20534711|pmc=2926754 |doi-access=free }}</ref>

Soon after the Big Bang, which occurred roughly 14 Gya, the only chemical elements present in the universe were hydrogen, helium, and lithium, the three lightest atoms in the periodic table. These elements gradually came together to form stars. These early stars were massive and short-lived, producing heavier elements through stellar nucleosynthesis. Carbon, currently the fourth most abundant chemical element in the universe (after hydrogen, helium and oxygen), was formed mainly in white dwarf stars, particularly those bigger than two solar masses.

宇宙大爆炸发生后不久，宇宙中仅存的化学元素是氢、氦和锂，这是21元素周期表中最轻的3个原子。这些元素逐渐聚集在一起形成了恒星。这些早期的恒星质量巨大，寿命短暂，在恆星核合成时期产生了较重的元素。碳，目前是宇宙中第四丰富的化学元素(仅次于氢、氦和氧) ，主要由白矮星形成，特别是那些大于两个太阳质量的恒星。

The concept of the RNA world was first proposed in 1962 by [[Alexander Rich]],<ref>{{cite journal |last1=Neveu |first1=Marc |last2=Kim |first2=Hyo-Joong |last3=Benner |first3=Steven A. |date=22 April 2013 |title=The 'Strong' RNA World Hypothesis: Fifty Years Old |journal=Astrobiology |volume=13 |issue=4 |pages=391–403 |bibcode=2013AsBio..13..391N |doi=10.1089/ast.2012.0868 |pmid=23551238 |ref=harv}}</ref> and the term was coined by [[Walter Gilbert]] in 1986.<ref name="Cech2012">{{cite journal |last=Cech |first=Thomas R. |authorlink=Thomas Cech |date=July 2012 |title=The RNA Worlds in Context |journal=Cold Spring Harbor Perspectives in Biology |volume=4 |issue=7 |page=a006742 |doi=10.1101/cshperspect.a006742 |pmc=3385955 |pmid=21441585}}</ref><ref>{{cite journal |last=Gilbert |first=Walter |authorlink=Walter Gilbert |date=20 February 1986 |title=Origin of life: The RNA world |journal=Nature |volume=319 |issue=6055 |page=618 |bibcode=1986Natur.319..618G |doi=10.1038/319618a0 |s2cid=8026658 }}</ref>

In March 2020, astronomer Tomonori Totani presented a statistical approach for explaining how an initial active RNA molecule might have been produced randomly in the [[universe]] sometime since the [[Big Bang]].<ref name="UT-20200310">{{cite news |last=Gough |first=Evan |title=Life Could be Common Across the Universe, Just Not in Our Region |url=https://www.universetoday.com/145304/life-could-be-common-across-the-universe-just-not-in-our-region/ |date=10 March 2020 |work=[[Universe Today]] |accessdate=15 March 2020 }}</ref><ref name="SR-20200203">{{cite journal |last=Totani |first=Tomonori |title=Emergence of life in an inflationary universe |date=3 February 2020 |journal=[[Scientific Reports]] |volume=10 |number=1671 |pages=1671 |doi=10.1038/s41598-020-58060-0 |pmid=32015390 |pmc=6997386 |arxiv=1911.08092 |bibcode=2020NatSR..10.1671T |doi-access=free }}</ref>

As these stars reached the end of their lifecycles, they ejected these heavier elements, among them carbon and oxygen, throughout the universe. These heavier elements allowed for the formation of new objects, including rocky planets and other bodies.

随着这些恒星的生命周期走到尽头，它们在宇宙中喷射出这些较重的元素，其中包括碳和氧。这些较重的元素形成了新的天体，包括岩石行星和其他天体。

===Phylogeny and LUCA===

[[File:Phylogenic Tree-en.svg|upright=1.65|thumb|A [[cladistics|cladogram]] demonstrating extreme [[hyperthermophile]]s as occur in volcanic hot springs at the base of the [[Phylogenetic tree|phylogenetic tree of life]].]]The most commonly accepted location of the root of the tree of life is between a monophyletic domain [[Bacteria]] and a clade formed by [[Archaea]] and [[Eukaryota]] of what is referred to as the "traditional tree of life" based on several molecular studies starting with [[Carl Woese]].<ref>{{cite book |editor1-first=David R. |editor1-last=Boone |editor2-first=Richard W. |editor2-last=Castenholz |editor3-first=George M. |editor3-last=Garrity |title=The ''Archaea'' and the Deeply Branching and Phototrophic ''Bacteria'' |series=Bergey's Manual of Systematic Bacteriology |isbn=978-0-387-21609-6 |url=https://www.springer.com/life+sciences/microbiology/book/978-0-387-98771-2 |url-status=live |archiveurl=https://web.archive.org/web/20141225112809/http://www.springer.com/life+sciences/microbiology/book/978-0-387-98771-2 |archivedate=25 December 2014|publisher=Springer |year=2001 }}{{page needed|date=June 2014}}</ref><ref>{{cite journal |vauthors=Woese CR, Fox GE |title= Phylogenetic structure of the prokaryotic domain: the primary kingdoms. |journal= Proc Natl Acad Sci U S A |volume=74|pages= 5088–5090 |year=1977 |issue= 11 |pmid=270744 |pmc=432104|doi=10.1073/pnas.74.11.5088|bibcode= 1977PNAS...74.5088W }}</ref>

According to the nebular hypothesis, the formation and evolution of the Solar System began 4.6 Gya with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

根据星云假说天文台的报道，太阳系的形成和演化始于4.6 Gya，其引力坍缩是一个巨大分子云的一小部分。大部分坍缩的质量聚集在中心，形成了太阳，而其余的塌缩成一个原行星盘，行星、卫星、小行星和其他小型太阳系天体由此形成。

A very small minority of studies have concluded differently, namely that the root is in the domain Bacteria, either in the phylum [[Firmicutes]]<ref>{{cite journal |vauthors=Valas RE, Bourne PE |title=The origin of a derived superkingdom: how a gram-positive bacterium crossed the desert to become an archaeon |journal=Biology Direct |volume=6 |page=16 |year=2011 |pmid=21356104 |pmc=3056875 |doi=10.1186/1745-6150-6-16}}</ref> or that the phylum [[Chloroflexi (phylum)|Chloroflexi]] is basal to a clade with Archaea+Eukaryotes and the rest of Bacteria as proposed by [[Thomas Cavalier-Smith]].<ref name=CS2>{{cite journal |author=Cavalier-Smith T |title=Rooting the tree of life by transition analyses |journal=Biology Direct |volume=1 |page=19 |year=2006 |pmid=16834776 |pmc=1586193 |doi=10.1186/1745-6150-1-19}}</ref> More recently, [[Peter Ward (paleontologist)|Peter Ward]] has proposed an alternative view which is rooted in abiotic RNA synthesis which becomes enclosed within a capsule and then creates RNA [[ribozyme]] replicates. It is proposed that this then bifurcates between Dominion Ribosa ([[RNA life]]), and after the loss of ribozymes RNA viruses as Domain Viorea, and Dominion Terroa{{clarify|date=August 2018}}, which after creating a large cell within a lipid wall, creating DNA the 20 based amino acids and the triplet code, is established as the [[last universal common ancestor]] or LUCA, of earlier phylogenic trees.<ref>{{cite book|last = Ward|first = Peter Douglas|date = 2005|title = Life as We Do Not Know it: The NASA Search for (and Synthesis Of) Alien Life|publisher = Viking Books|isbn = 978-0670034581|url = https://archive.org/details/lifeaswedonotkno00ward}}</ref>

The Earth, formed 4.5 Gya, was at first inhospitable to any living organisms. Based on numerous observations and studies of the geological time-scale, the Hadean Earth is thought to have had a secondary atmosphere, formed through degassing of the rocks that accumulated from planetesimal impactors. At first, it was thought that the Earth's atmosphere consisted of hydrogen compounds—methane, ammonia and Water vapor—and that life began under such reducing conditions, which are conducive to the formation of organic molecules. According to later models, suggested by studying ancient minerals, the atmosphere in the late Hadean period consisted largely of water vapor, nitrogen and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen, and sulfur compounds. During its formation, the Earth lost a significant part of its initial mass, with a nucleus of the heavier rocky elements of the protoplanetary disk remaining. As a consequence, Earth lacked the gravity to hold any molecular hydrogen in its atmosphere, and rapidly lost it during the Hadean period, along with the bulk of the original inert gases. The solution of carbon dioxide in water is thought to have made the seas slightly acidic, giving them a pH of about 5.5. The atmosphere at the time has been characterized as a "gigantic, productive outdoor chemical laboratory." This scenario has found support from the dating of 4.404  Gyo zircon crystals from metamorphosed quartzite of Mount Narryer in the Western Australia Jack Hills of the Pilbara, which provide evidence that oceans and continental crust existed within 150 Ma of Earth's formation. Despite the likely increased volcanism and existence of many smaller tectonic "platelets," it has been suggested that between 4.4-4.3 Gyo, the Earth was a water world, with little if any continental crust, an extremely turbulent atmosphere and a hydrosphere subject to intense ultraviolet (UV) light, from a T Tauri stage Sun, cosmic radiation and continued bolide impacts.

形成于4.5 Gya 的地球起初对任何生物都不适宜居住。根据对地质时间尺度的大量观察和研究，人们认为 Hadean Earth 有一个次级大气层，是通过对星子撞击物所积累的岩石进行排气而形成的。起初，人们认为地球的大气层由氢化合物(甲烷、氨和水蒸气)组成，生命是在这种还原条件下开始的，这种还原条件有利于有机分子的形成。根据后来的模型，根据对古代矿物的研究，在哈迪亚晚期的大气主要由水蒸气、氮气和二氧化碳组成，还有少量的一氧化碳、氢气和硫化合物。在其形成过程中，地球失去了其初始质量的一个重要部分，而原行星盘中较重的岩石元素的原子核仍然存在。因此，地球没有足够的重力在其大气中容纳氢分子，并且在哈迪恩时期迅速失去了氢分子，同时失去了大部分原始的惰性气体。二氧化碳在水中形成的溶液被认为使海洋呈微酸性，pH 值约为5.5。当时的大气被描述为一个“巨大的、多产的户外化学实验室”这一假设得到了来自西澳大利亚皮尔巴拉杰克山的变质石英岩中4.404 Gyo 锆石晶体的年代测定的支持，这提供了海洋和大陆地壳存在于地球形成150ma 内的证据。尽管火山活动可能增加，并存在许多小型的构造“血小板” ，但有人认为，在4.4-4.3 Gyo 之间，地球是一个水世界，几乎没有大陆地壳，一个极其动荡的大气层和一个受到来自 t Tauri 阶段太阳的强烈紫外线(UV)、宇宙辐射和持续的火流冲击的水圈。

In 2016, a set of 355 [[gene]]s likely present in the [[Last Universal Common Ancestor]] (LUCA) of all [[organism]]s [[Life|living on Earth]] was identified.<ref name="NYT-20160725">{{cite news |last=Wade |first=Nicholas |authorlink=Nicholas Wade |title=Meet Luca, the Ancestor of All Living Things |url=https://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html |date=25 July 2016 |work=[[The New York Times]] |url-status=live |archiveurl=https://web.archive.org/web/20160728053822/http://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html |archivedate=28 July 2016}}</ref> A total of 6.1 million prokaryotic protein coding genes from various phylogenic trees were sequenced, identifying 355 protein clusters from amongst 286,514 protein clusters that were probably common to LUCA. The results

<blockquote>. . . depict LUCA as [[Anaerobic organism|anaerobic]], CO2-fixing, H2-dependent with a [[Wood–Ljungdahl pathway]], N2-fixing and thermophilic. LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms. Its [[Cofactor (biochemistry)|cofactors]] reveal dependence upon [[transition metal]]s, [[Flavin mononucleotide|flavins]], [[S-adenosyl methionine]], [[coenzyme A]], [[ferredoxin]], [[molybdopterin]], [[corrin]]s and [[selenium]]. Its genetic code required [[nucleoside]] modifications and S-adenosylmethionine-dependent [[methylation]]s."

</blockquote>The results depict [[methanogen]]ic [[clostridium|clostridia]] as a basal clade in the 355 phylogenies examined, and suggest that LUCA inhabited an anaerobic [[hydrothermal vent]] setting in a geochemically active environment rich in H2, CO2 and iron.<ref>{{cite journal |doi=10.1038/NMICROBIOL.2016.116 | volume=1 | issue=9 | title=The physiology and habitat of the last universal common ancestor | journal=Nature Microbiology | page=16116 | pmid=27562259 | last1=Weiss | first1=M.C. | last2=Sousa | first2=F.L. | last3=Mrnjavac | first3=N. | last4=Neukirchen | first4=S. | last5=Roettger | first5=M. | last6=Nelson-Sathi | first6=S. | last7=Martin | first7=W.F.| year=2016 | s2cid=2997255 | url=https://zenodo.org/record/3451085 }}</ref>

The Hadean environment would have been highly hazardous to modern life. Frequent collisions with large objects, up to 500 km in diameter, would have been sufficient to sterilize the planet and vaporize the oceans within a few months of impact, with hot steam mixed with rock vapor becoming high altitude clouds that would completely cover the planet. After a few months, the height of these clouds would have begun to decrease but the cloud base would still have been elevated for about the next thousand years. After that, it would have begun to rain at low altitude. For another two thousand years, rains would slowly have drawn down the height of the clouds, returning the oceans to their original depth only 3,000 y after the impact event.

哈迪亚的环境对现代生活来说是非常危险的。与直径达500公里的大型天体频繁碰撞，足以使地球灭绝，并在几个月的碰撞后蒸发海洋，热蒸汽与岩石蒸汽混合形成高空云，完全覆盖地球。几个月后，这些云层的高度将开始下降，但是在接下来的几千年里，云层的基础仍然会升高。在那之后，低海拔地区就会开始下雨。在接下来的2000年里，降雨会慢慢降低云层的高度，使海洋在撞击事件发生后仅仅3000年就恢复到原来的深度。

A study at the University of Düsseldorf created [[phylogeny|phylogenic trees]] based upon 6 million genes from [[bacteria]] and [[archaea]], and identified 355 protein families that were probably present in the [[LUCA]]. They were based upon an anaerobic metabolism fixing [[carbon dioxide]] and [[nitrogen]]. It suggests that the LUCA evolved in an environment rich in [[hydrogen]], carbon dioxide and [[iron]].<ref>Nature Vol 535, 28 July 2016,"Early Life Liked it Hot", p.468</ref>

Traditionally it was thought that during the period between 4.28 that pockmarked the Moon and the other inner planets (Mercury, Mars, and presumably Earth and Venus). This would likely have repeatedly sterilized the planet, had life appeared before that time. Internal heating as a result of gravitational sorting between the core and the mantle would have caused a great deal of mantle convection, with the probable result of many more smaller and more active tectonic plates than now exist.

传统上认为，在4.28之间的时期，月球和其他内行星(水星，火星，可能还有地球和金星)坑坑洼洼。如果生命在那个时间之前出现的话，这可能会反复地使地球灭绝。由于地核和地幔之间的重力分选，内热可能产生了大量的地幔对流，可能导致了比现在存在的更小更活跃的构造板块。

===Key issues in abiogenesis===

The time periods between such devastating environmental events give time windows for the possible origin of life in the early environments. If the deep marine hydrothermal setting was the site for the origin of life, then abiogenesis could have happened as early as 4.0-4.2 Gya. If the site was at the surface of the Earth, abiogenesis could only have occurred between 3.7-4.0 Gya.

这些毁灭性环境事件之间的时间间隔为早期环境中可能的生命起源提供了时间窗口。如果深海热液环境是生命起源的场所，那么早在4.0-4.2 Gya 就可能发生了自生作用。如果该地点位于地球表面，那么自然发生只可能发生在3.7-4.0 Gya 之间。

====What came first: protein or nucleic acids?====

Possible precursors for the evolution of protein synthesis include a mechanism to synthesize short peptide cofactors or form a mechanism for the duplication of RNA. It is likely that the ancestral ribosome was composed entirely of RNA, although some roles have since been taken over by proteins. Major remaining questions on this topic include identifying the selective force for the evolution of the ribosome and determining how the [[genetic code]] arose.<ref name="Noller2012">{{cite journal |last=Noller |first=Harry F. |authorlink=Harry F. Noller |date=April 2012 |title=Evolution of protein synthesis from an RNA world. |journal=Cold Spring Harbor Perspectives in Biology |volume=4 |issue=4 |page=a003681 |doi=10.1101/cshperspect.a003681 |pmc=3312679 |pmid=20610545}}</ref>

Estimates of the production of organics from these sources suggest that the Late Heavy Bombardment before 3.5 Ga within the early atmosphere made available quantities of organics comparable to those produced by terrestrial sources.

根据对这些来源生成的有机物的估计，早期大气中3.5 Ga 之前的后期重轰炸期使得有机物的数量可与陆地来源生成的数量相媲美。

[[Eugene Koonin]] said, <blockquote>Despite considerable experimental and theoretical effort, no compelling scenarios currently exist for the origin of replication and translation, the key processes that together comprise the core of biological systems and the apparent pre-requisite of biological evolution. The RNA World concept might offer the best chance for the resolution of this conundrum but so far cannot adequately account for the emergence of an efficient RNA replicase or the translation system. The MWO ["many worlds in one"] version of the cosmological model of [[eternal inflation]] could suggest a way out of this conundrum because, in an infinite [[multiverse]] with a finite number of distinct macroscopic histories (each repeated an infinite number of times), emergence of even highly complex systems by chance is not just possible but inevitable.<ref name="pmc1892545">{{cite journal |last=Koonin |first=Eugene V. |date=31 May 2007 |title=The cosmological model of eternal inflation and the transition from chance to biological evolution in the history of life |journal=Biology Direct |volume=2 |page=15 |doi=10.1186/1745-6150-2-15 |pmc=1892545 |pmid=17540027}}</ref></blockquote>

It has been estimated that the Late Heavy Bombardment may also have effectively sterilized the Earth's surface to a depth of tens of meters. If life evolved deeper than this, it would have also been shielded from the early high levels of ultraviolet radiation from the T Tauri stage of the Sun's evolution. Simulations of geothermically heated oceanic crust yield far more organics than those found in the Miller–Urey experiments. In the deep hydrothermal vents, Everett Shock has found "there is an enormous thermodynamic drive to form organic compounds, as seawater and hydrothermal fluids, which are far from equilibrium, mix and move towards a more stable state." Shock has found that the available energy is maximized at around 100–150 C, precisely the temperatures at which the hyperthermophilic bacteria and thermoacidophilic archaea have been found, at the base of the phylogenetic tree of life closest to the Last Universal Common Ancestor (LUCA).

据估计，后期重轰炸期空间站可能也有效地消毒了地球表面到几十米深的地方。如果生命进化得比这还要深，那么它也可以免受来自太阳进化的 t Tauri 阶段的早期高水平紫外线辐射的影响。地热加热的海洋地壳模拟产生的有机物远远多于 Miller-Urey 实验中发现的有机物。在深海热液喷口，埃弗里特休克发现“有一个巨大的热力学驱动力形成有机化合物，作为海水和热液流体，这是远离平衡，混合和移动到一个更稳定的状态研究人员发现，可利用的能量在100-150摄氏度左右达到最大值，这个温度恰好是在最接近最后一个共同祖先的生命系统发生树的底部发现极端嗜热菌和嗜热古菌的温度。

====Emergence of the genetic code====

See: [[Genetic code#Origin|Genetic code]].

[[Precambrian stromatolites in the Siyeh Formation, Glacier National Park.

[冰川国家公园寺耶组的前寒武纪叠层石。

====Error in translation catastrophe====

A 2002 study suggested that these 3.5 Gyo (billion year old) formations contain fossilized cyanobacteria microbes. This suggests they are evidence of one of the earliest life forms on Earth.]]

2002年的一项研究表明，这些3.5 Gyo (亿年前)的形成包含化石蓝细菌微生物。这表明它们是地球上最早的生命形式之一的证据。]

Hoffmann has shown that an early error-prone translation machinery can be stable against an error catastrophe of the type that had been envisaged as problematical for the origin of life, and was known as "Orgel's paradox".<ref>{{cite journal |last=Hoffmann |first=Geoffrey W. |authorlink=Geoffrey W. Hoffmann |date=25 June 1974 |title=On the origin of the genetic code and the stability of the translation apparatus |journal=[[Journal of Molecular Biology]] |volume=86 |issue=2 |pages=349–362 |doi=10.1016/0022-2836(74)90024-2 |pmid=4414916}}</ref><ref>{{cite journal |last=Orgel |first=Leslie E. |date=April 1963 |title=The Maintenance of the Accuracy of Protein Synthesis and its Relevance to Ageing |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=49 |issue=4 |pages=517–521 |bibcode=1963PNAS...49..517O |doi=10.1073/pnas.49.4.517 |pmc=299893 |pmid=13940312}}</ref><ref>{{cite journal |last=Hoffmann |first=Geoffrey W. |title=The Stochastic Theory of the Origin of the Genetic Code |date=October 1975 |journal=[[Annual Review of Physical Chemistry]] |volume=26 |pages=123–144 |bibcode=1975ARPC...26..123H |doi=10.1146/annurev.pc.26.100175.001011 }}</ref>

Stromatolites in [[Shark Bay]]

在[[鲨鱼湾]]的叠层石

The earliest life on Earth existed more than 3.5 Gya (billion years ago), This finding suggested life developed very soon after oceans formed. The structure of the microbes was noted to be similar to bacteria found near hydrothermal vents in the modern era, and provided support for the hypothesis that abiogenesis began near hydrothermal vents. and microbial mat fossils found in 3.48 Gyo sandstone from Western Australia. Evidence of early life in rocks from Akilia Island, near the Isua supracrustal belt in southwestern Greenland, dating to 3.7 Gya have shown biogenic carbon isotopes. In other parts of the Isua supracrustal belt, graphite inclusions trapped within garnet crystals are connected to the other elements of life: oxygen, nitrogen, and possibly phosphorus in the form of phosphate, providing further evidence for life 3.7 Gya. At Strelley Pool, in the Pilbara region of Western Australia, compelling evidence of early life was found in pyrite-bearing sandstone in a fossilized beach, that showed rounded tubular cells that oxidized sulfur by photosynthesis in the absence of oxygen. Further research on zircons from Western Australia in 2015 suggested that life likely existed on Earth at least 4.1 Gya.

地球上最早的生命存在于35亿年前，这一发现表明生命在海洋形成后不久就发展了。这些微生物的结构与现代在热液喷口附近发现的细菌十分相似，这为自然生成始于热液喷口附近的假说提供了支持。以及在西澳大利亚3.48 Gyo 砂岩中发现的微生物垫状化石。格陵兰西南部伊苏阿表壳带附近的阿基利亚岛岩石中早期生命的证据表明，生物碳同位素年龄为3.7 Gya。在 Isua 表壳带的其他部分，石榴石晶体中的石墨包裹体与其他生命元素相连: 氧、氮，可能还有磷酸盐形式的磷，这为生命提供了进一步的证据3.7 Gya。在西澳大利亚皮尔巴拉地区的 Strelley Pool，在化石海滩中含黄铁矿的砂岩中发现了早期生命的令人信服的证据，证明了圆形的管状细胞在缺氧的情况下通过光合作用氧化硫。2015年对澳大利亚西部锆石的进一步研究表明，地球上可能至少存在4.1 Gya 生命。

====Homochirality====

{{Main|Homochirality}}

Homochirality refers to a geometric uniformity of some materials composed of [[chirality|chiral]] units. Chiral refers to nonsuperimposable 3D forms that are mirror images of one another, as are left and right hands. Living organisms use molecules that have the same chirality ("handedness"): with almost no exceptions,<ref>{{harvnb|Chaichian|Rojas|Tureanu|2014|pp=353–364}}</ref> amino acids are left-handed while nucleotides and [[Carbohydrate|sugars]] are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral [[Catalysis|catalyst]], they are formed in a 50/50 mixture of both [[enantiomer]]s (called a racemic mixture). Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the [[electroweak interaction]]; asymmetric environments, such as those caused by [[Circular polarization|circularly polarized]] light, [[Quartz|quartz crystals]], or the Earth's rotation, [[statistical fluctuations]] during racemic synthesis,<ref name="Plasson2007">{{cite journal |last1=Plasson |first1=Raphaël |last2=Kondepudi |first2=Dilip K. |last3=Bersini |first3=Hugues |last4=Commeyras |first4=Auguste |last5=Asakura |first5=Kouichi |display-authors=3 |date=August 2007 |title=Emergence of homochirality in far-from-equilibrium systems: Mechanisms and role in prebiotic chemistry |journal=[[Chirality (journal)|Chirality]] |volume=19 |issue=8 |pages=589–600 |doi=10.1002/chir.20440 |pmid=17559107}} "Special Issue: Proceedings from the Eighteenth International Symposium on Chirality (ISCD-18), Busan, Korea, 2006"</ref> and [[spontaneous symmetry breaking]].<ref name="jafarpour2017">{{cite journal |last1=Jafarpour |first1=Farshid |last2=Biancalani |first2=Tommaso |last3=Goldenfeld |first3=Nigel |year=2017 |title=Noise-induced symmetry breaking far from equilibrium and the emergence of biological homochirality |journal=Physical Review E |volume=95 |issue=3 |pages=032407 |doi=10.1103/PhysRevE.95.032407|pmid=28415353 |bibcode=2017PhRvE..95c2407J |url=http://dspace.mit.edu/bitstream/1721.1/109170/1/PhysRevE.95.032407.pdf }}</ref><ref name="jafarpour2015">{{cite journal |last1=Jafarpour |first1=Farshid |last2=Biancalani |first2=Tommaso |last3=Goldenfeld |first3=Nigel |year=2015 |title=Noise-induced mechanism for biological homochirality of early life self-replicators |journal=Physical Review Letters |volume=115 |issue=15 |pages=158101 |doi=10.1103/PhysRevLett.115.158101|pmid=26550754 |arxiv=1507.00044 |bibcode=2015PhRvL.115o8101J |s2cid=9775791 }}</ref><ref name="frank1953">{{cite journal |last1=Frank |first1=F.C. |year=1953 |title=On spontaneous asymmetric synthesis |journal=Biochimica et Biophysica Acta |volume=11 |issue=4 |pages=459–463 |doi=10.1016/0006-3002(53)90082-1|pmid=13105666 }}</ref>

Once established, chirality would be selected for.<ref>{{cite journal |last=Clark |first=Stuart |authorlink=Stuart Clark (author) |date=July–August 1999 |title=Polarized Starlight and the Handedness of Life |journal=[[American Scientist]] |volume=87 |issue=4 |page=336 |bibcode=1999AmSci..87..336C |doi=10.1511/1999.4.336}}</ref> A small bias ([[enantiomeric excess]]) in the population can be amplified into a large one by [[Autocatalysis#Asymmetric autocatalysis|asymmetric autocatalysis]], such as in the [[Soai reaction]].<ref>{{cite journal |last1=Shibata |first1=Takanori |last2=Morioka |first2=Hiroshi |last3=Hayase |first3=Tadakatsu |last4=Choji |first4=Kaori |last5=Soai |first5=Kenso |display-authors=3 |date=17 January 1996 |title=Highly Enantioselective Catalytic Asymmetric Automultiplication of Chiral Pyrimidyl Alcohol |journal=Journal of the American Chemical Society |volume=118 |issue=2 |pages=471–472 |doi=10.1021/ja953066g }}</ref> In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other.<ref name="Soai2001">{{cite journal |last1=Soai |first1=Kenso |last2=Sato |first2=Itaru |last3=Shibata |first3=Takanori |year=2001 |title=Asymmetric autocatalysis and the origin of chiral homogeneity in organic compounds |journal=The Chemical Record |volume=1 |issue=4 |pages=321–332 |doi=10.1002/tcr.1017 |pmid=11893072}}</ref>

Panspermia is the hypothesis that life exists throughout the universe, distributed by meteoroids, asteroids, comets and planetoids.

胚种说是一种假说，认为生命存在于整个宇宙，由流星体、小行星、彗星和小行星分布。

Clark has suggested that homochirality may have started in outer space, as the studies of the amino acids on the [[Murchison meteorite]] showed that [[Alanine|L-alanine]] is more than twice as frequent as its D form, and [[Glutamic acid|L-glutamic acid]] was more than three times prevalent than its D counterpart. Various chiral crystal surfaces can also act as sites for possible concentration and assembly of chiral monomer units into macromolecules.<ref>{{harvnb|Hazen|2005|p=184}}</ref><ref name=Meierhenrich>{{cite book|last1=Meierhenrich|first1=Uwe|title=Amino acids and the asymmetry of life caught in the act of formation|date=2008|publisher=Springer|location=Berlin|isbn=978-3540768869|pages=76–79}}</ref> Compounds found on meteorites suggest that the chirality of life derives from abiogenic synthesis, since amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, the same as found in living organisms.<ref name=StarStuff>{{cite journal |last=Mullen |first=Leslie |date=5 September 2005 |title=Building Life from Star-Stuff |url=http://www.astrobio.net/news-exclusive/building-life-from-star-stuff/ |journal=[[Astrobiology Magazine]] |accessdate=2015-06-15 |url-status=live |archiveurl=https://web.archive.org/web/20150714084344/http://www.astrobio.net/news-exclusive/building-life-from-star-stuff/ |archivedate=14 July 2015}}</ref>

The panspermia hypothesis does not attempt to explain how life first originated but merely shifts the origin to another planet or a comet. The advantage of an extraterrestrial origin of primitive life is that life is not required to have formed on each planet it occurs on, but rather in a single location, and then spread about the galaxy to other star systems via cometary and/or meteorite impact.

胚种论假说并不试图解释生命最初是如何起源的，而仅仅是将起源地转移到另一个行星或彗星上。原始生命起源于地外的优势在于，不要求生命形成于它所在的每一个行星，而是在一个单一的位置，然后通过彗星和/或陨石的撞击，在星系中传播到其他星系。

Evidence for the panspermia hypothesis is scant, but it finds some support in studies of Martian meteorites found in Antarctica and in studies of extremophile microbes' survival in outer space tests.

有关胚种假说的证据很少，但在对南极洲发现的火星陨石的研究以及对极端微生物在外层空间生存的研究中，它找到了一些支持。

== Early universe and Earth: astronomy and geology ==

{{Main|Timeline of the evolutionary history of life}}

In August 2020, scientists reported that bacteria from Earth, particularly Deinococcus radiodurans, which is highly resistant to environmental hazards, were found to survive for three years in outer space, based on studies conducted on the International Space Station.

2020年8月，根据国际空间站的研究，科学家报告说，来自地球的细菌，特别是对环境危害具有高度抗性的抗辐射奇异球菌，被发现在外层空间存活了三年。

{{See also|Chronology of the Universe}}

{{See also|Geological history of Earth}}

An extreme speculation is that the biochemistry of life could have begun as early as 17 My (million years) after the Big Bang, during a habitable epoch, and that life may exist throughout the universe.

一个极端的推测是，生命的生物化学可能早在宇宙大爆炸之后的17my (百万年)时期就已经开始，那时正处于适宜居住的时期，而且生命可能存在于整个宇宙中。

===Early universe with first stars===

{{Nature timeline}} {{Life timeline}}

Soon after the [[Big Bang]], which occurred roughly 14 Gya, the only chemical elements present in the universe were hydrogen, helium, and lithium, the three lightest atoms in the periodic table. These elements gradually came together to form stars. These early stars were massive and short-lived, producing heavier elements through [[stellar nucleosynthesis]]. [[Carbon]], currently the [[Abundance of the chemical elements|fourth most abundant chemical element]] in the universe (after [[hydrogen]], [[helium]] and [[oxygen]]), was formed mainly in [[white dwarf stars]], particularly those bigger than two solar masses.<ref name="INV-20200706">{{cite news|last=Rabie|first=Passant|date=6 July 2020|title=Astronomers Have Found The Source Of Life In The Universe|work=[[Inverse (website)|Inverse]]|url=https://www.inverse.com/science/carbon-from-white-dwarfs|accessdate=7 July 2020}}</ref><ref name="NA-20200706">{{cite journal|author=Marigo, Paola|display-authors=et al.|date=6 July 2020|title=Carbon star formation as seen through the non-monotonic initial–final mass relation|url=https://www.nature.com/articles/s41550-020-1132-1|journal=[[Nature Astronomy]]|volume=152|arxiv=2007.04163|doi=10.1038/s41550-020-1132-1|bibcode=2020NatAs.tmp..143M|accessdate=7 July 2020|s2cid=220403402}}</ref>

Carl Zimmer has speculated that the chemical conditions, including the presence of boron, molybdenum and oxygen needed for the initial production of RNA, may have been better on early Mars than on early Earth. If so, life-suitable molecules originating on Mars may have later migrated to Earth via meteor ejections.

卡尔 · 齐默推测，早期火星上的化学条件，包括最初生成 RNA 所需的硼、钼和氧的存在，可能比早期地球上的情况要好。如果是这样的话，原产于火星的适合生命的分子可能随后通过流星喷射迁移到地球。

As these stars reached the end of their [[Stellar life cycle|lifecycles]], they ejected these heavier elements, among them carbon and oxygen, throughout the universe. These heavier elements allowed for the formation of new objects, including rocky planets and other bodies.<ref>{{Cite web | url=https://wmap.gsfc.nasa.gov/universe/uni_life.html |title = WMAP- Life in the Universe}}</ref>

===Emergence of the Solar System===

According to the [[nebular hypothesis]], the formation and evolution of the [[Solar System]] began 4.6 Gya with the [[gravitational collapse]] of a small part of a giant [[molecular cloud]].<ref>[http://www.astro.umass.edu/~myun/teaching/a100_old/solarnebulartheory.htm Formation of Solar Systems: Solar Nebular Theory.] University of Massachusetts Amherst, Department of Astronomy. Accessed on 27 September 2019.</ref> Most of the collapsing mass collected in the center, forming the [[Sun]], while the rest flattened into a [[protoplanetary disk]] out of which the [[planet]]s, [[Natural satellite|moons]], [[asteroid]]s, and other [[Small Solar System body|small Solar System bodies]] formed.

Traditional religion attributed the origin of life to supernatural deities who created the natural world. Spontaneous generation, the first naturalistic theory of life arising from non-life, goes back to Aristotle and ancient Greek philosophy, and continued to have support in Western scholarship until the 19th century. Classical notions of spontaneous generation held that certain "lower" or "vermin" animals are generated by decaying organic substances. According to Aristotle, it was readily observable that aphids arise from dew on plants, flies from putrid matter, mice from dirty hay, crocodiles from rotting sunken logs, and so on. A related theory was heterogenesis: that some forms of life could arise from different forms (e.g. bees from flowers). The modern scientist John Bernal said that the basic idea of such theories was that life was continuously created as a result of chance events.

传统宗教把生命的起源归因于创造自然界的超自然神灵。自然发生，第一个源于非生命的自然主义生命理论，可以追溯到亚里士多德和古希腊哲学，一直得到西方学术界的支持，直到19世纪。自然发生的古典观念认为，某些“低等”或“害虫”动物是由腐烂的有机物质产生的。根据亚里士多德的理论，很容易观察到蚜虫是由植物上的露水生成的，苍蝇是由腐烂的物质生成的，老鼠是由肮脏的干草生成的，鳄鱼是由腐烂的木头生成的，等等。一个相关的理论是异种发生: 某些形式的生命可能来自不同的形式(例如:。蜜蜂来自花朵)。现代科学家约翰 · 伯纳尔说，这些理论的基本思想是，生命是由偶然事件不断创造出来的。

===Emergence of Earth===

In the 17th century, people began to question such assumptions. In 1646, Thomas Browne published his Pseudodoxia Epidemica (subtitled Enquiries into Very many Received Tenets, and commonly Presumed Truths), which was an attack on false beliefs and "vulgar errors." His contemporary, Alexander Ross, erroneously refuted him, stating:<blockquote> To question this [spontaneous generation], is to question Reason, Sense, and Experience: If he doubts of this, let him go to Ægypt, and there he will find the fields swarming with mice begot of the mud of Nylus, to the great calamity of the Inhabitants.</blockquote>

在17世纪，人们开始质疑这种假设。1646年，托马斯 · 布朗出版了他的《伪多西亚词典》(Pseudodoxia 耀龙，副标题是对许多公认教义和普遍认为的真相的调查) ，这本书攻击了错误的信仰和“庸俗的错误”与他同时代的 Alexander Ross 错误地驳斥了他的观点，他说: 质疑这个[自然发生] ，就是质疑理性、感觉和经验: 如果他对此有所怀疑，就让他去 Ægypt，在那里他会发现满是老鼠的田野生出了 Nylus 的泥浆，给居民带来了巨大的灾难。</blockquote >

The Earth, formed 4.5 Gya, was at first inhospitable to any living organisms. Based on numerous observations and studies of the [[geological time scale|geological time-scale]], the [[Hadean]] Earth is thought to have had a [[secondary atmosphere]], formed through [[Degasification|degassing]] of the rocks that accumulated from [[planetesimal]] [[impact event|impactors]]. At first, it was thought that the Earth's [[atmosphere]] consisted of hydrogen compounds—[[methane]], [[ammonia]] and [[Water vapor]]—and that life began under such [[redox|reducing]] conditions, which are conducive to the formation of organic molecules. According to later models, suggested by studying ancient minerals, the atmosphere in the late Hadean period consisted largely of water vapor, [[nitrogen]] and [[carbon dioxide]], with smaller amounts of [[carbon monoxide]], [[hydrogen]], and [[sulfur]] compounds.<ref>{{cite journal |last=Kasting |first=James F. |authorlink=James Kasting |date=12 February 1993 |title=Earth's Early Atmosphere |url=http://wwwdca.iag.usp.br/www/material/fornaro/ACA410/Kasting%201993_EarthEarlyAtmos.pdf |journal=Science |volume=259 |issue=5097 |pages=920–926 |doi=10.1126/science.11536547 |pmid=11536547 |bibcode=1993Sci...259..920K |s2cid=21134564 |accessdate=2015-07-28 |ref=harv |url-status=dead |archiveurl=https://web.archive.org/web/20151010074651/http://wwwdca.iag.usp.br/www/material/fornaro/ACA410/Kasting%201993_EarthEarlyAtmos.pdf |archivedate=10 October 2015}}</ref> During its formation, the Earth lost a significant part of its initial mass, with a nucleus of the heavier rocky elements of the protoplanetary disk remaining.<ref>{{harvnb|Fesenkov|1959|p=9}}</ref> As a consequence, Earth lacked the [[gravity]] to hold any molecular hydrogen in its atmosphere, and rapidly lost it during the Hadean period, along with the bulk of the original inert gases. The solution of carbon dioxide in water is thought to have made the seas slightly [[acid]]ic, giving them a [[pH]] of about 5.5.<ref>{{Cite journal|last=Morse|first=John|date=September 1998|title=Hadean Ocean Carbonate Geochemistry|journal=Aquatic Geochemistry|volume=4|issue=3/4|pages=301–319|doi=10.1023/A:1009632230875|bibcode=1998MinM...62.1027M|s2cid=129616933}}</ref> The atmosphere at the time has been characterized as a "gigantic, productive outdoor chemical laboratory."<ref name="Follmann2009" /> It may have been similar to the mixture of gases released today by volcanoes, which still support some abiotic chemistry.<ref name="Follmann2009" />

Antonie van Leeuwenhoek

Antonie van Leeuwenhoek

===Emergence of the ocean===

In 1665, Robert Hooke published the first drawings of a microorganism. Hooke was followed in 1676 by Antonie van Leeuwenhoek, who drew and described microorganisms that are now thought to have been protozoa and bacteria. Many felt the existence of microorganisms was evidence in support of spontaneous generation, since microorganisms seemed too simplistic for sexual reproduction, and asexual reproduction through cell division had not yet been observed. Van Leeuwenhoek took issue with the ideas common at the time that fleas and lice could spontaneously result from putrefaction, and that frogs could likewise arise from slime. Using a broad range of experiments ranging from sealed and open meat incubation and the close study of insect reproduction he became, by the 1680s, convinced that spontaneous generation was incorrect.

1665年，罗伯特 · 胡克出版了第一幅关于微生物的图画。1676年，胡克紧随安东尼·范·列文虎克之后，绘制并描述了现在被认为是原生动物和细菌的微生物。许多人认为微生物的存在是支持自然发生的证据，因为微生物对有性生殖来说似乎过于简单化了，而无性生殖通过细胞分裂的过程还没有被观察到。范 · 列文虎克对当时普遍的观点提出了异议，即跳蚤和虱子可能由腐烂自发产生，青蛙同样也可能由粘液产生。到了17世纪80年代，通过大量的实验，包括密封和开放的肉类孵化和对昆虫繁殖的深入研究，他确信自然发生是错误的。

[[Origin of water on Earth|Oceans]] may have [[Cool early Earth|appeared first]] in the Hadean Eon, as soon as 200 My after the Earth formed, in a hot, 100 C, reducing environment, and the pH of about 5.8 rose rapidly towards neutral.<ref>{{cite journal |last1=Morse |first1=John W. |last2=MacKenzie |first2=Fred T. |authorlink2=Fred T. Mackenzie (scientist) |year=1998 |title=Hadean Ocean Carbonate Geochemistry |journal=Aquatic Geochemistry |volume=4 |issue=3–4 |pages=301–319 |doi=10.1023/A:1009632230875 |bibcode=1998MinM...62.1027M |s2cid=129616933 }}</ref> This scenario has found support from the dating of 4.404  Gyo [[zircon]] crystals from metamorphosed [[quartzite]] of [[Narryer Gneiss Terrane|Mount Narryer]] in the Western Australia [[Jack Hills]] of the [[Pilbara]], which provide evidence that oceans and [[continental crust]] existed within 150 [[Ma (unit)|Ma]] of Earth's formation.<ref name="Wilde2001">{{cite journal |last1=Wilde |first1=Simon A. |last2=Valley |first2=John W. |last3=Peck |first3=William H. |last4=Graham |first4=Colin M. |date=11 January 2001 |title=Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago |url=http://www.geology.wisc.edu/~valley/zircons/Wilde2001Nature.pdf |journal=[[Nature (journal)|Nature]] |volume=409 |issue=6817 |pages=175–178 |doi=10.1038/35051550 |pmid=11196637 |accessdate=2015-06-03 |url-status=live |archiveurl=https://web.archive.org/web/20150605132344/http://www.geology.wisc.edu/~valley/zircons/Wilde2001Nature.pdf |archivedate=5 June 2015|bibcode=2001Natur.409..175W |s2cid=4319774 }}</ref> Despite the likely increased volcanism and existence of many smaller [[Plate tectonics|tectonic]] "platelets," it has been suggested that between 4.4-4.3 Gyo, the Earth was a water world, with little if any continental crust, an extremely [[turbulence|turbulent]] atmosphere and a [[hydrosphere]] subject to intense [[ultraviolet]] (UV) light, from a [[T Tauri star|T Tauri stage Sun]], [[Cosmic ray|cosmic radiation]] and continued [[bolide]] impacts.<ref name="rise.2006">{{cite journal |last1=Rosing |first1=Minik T. |last2=Bird |first2=Dennis K. |last3=Sleep |first3=Norman H. |last4=Glassley |first4=William |last5=Albarède |first5=Francis |authorlink5=Francis Albarède |display-authors=3 |date=22 March 2006 |title=The rise of continents – An essay on the geologic consequences of photosynthesis |url= https://www.researchgate.net/publication/223066196|journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=232 |issue=2–4 |pages=99–113 |doi=10.1016/j.palaeo.2006.01.007 |accessdate=2015-06-08 |url-status=live |archiveurl=https://web.archive.org/web/20150714073656/http://www.researchgate.net/profile/Francis_Albarede/publication/223066196_The_rise_of_continentsAn_essay_on_the_geologic_consequences_of_photosynthesis/links/00b7d51766c442f58b000000.pdf |archivedate=14 July 2015|bibcode=2006PPP...232...99R }}</ref>

The first experimental evidence against spontaneous generation came in 1668 when Francesco Redi showed that no maggots appeared in meat when flies were prevented from laying eggs. It was gradually shown that, at least in the case of all the higher and readily visible organisms, the previous sentiment regarding spontaneous generation was false. The alternative hypothesis was biogenesis: that every living thing came from a pre-existing living thing (omne vivum ex ovo, Latin for "every living thing from an egg"). In 1768, Lazzaro Spallanzani demonstrated that microbes were present in the air, and could be killed by boiling. In 1861, Louis Pasteur performed a series of experiments that demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media, but could only appear by invasion from without.

第一个针对自然发生的实验证据出现在1668年，当时 Francesco Redi 表明，当苍蝇被阻止产卵时，肉中不会出现蛆。人们逐渐发现，至少对于所有高等且容易观察到的生物来说，之前关于自然发生的观点是错误的。另一种假设是生物起源: 每一个生物都来自一个已经存在的生物(omne vivum ex ovo，拉丁语“每一个生物都来自一个蛋”)。1768年，医生证明空气中存在微生物，煮沸可以杀死微生物。1861年，路易斯 · 巴斯德进行了一系列实验，证明细菌和真菌等生物体不会自发地出现在无菌的、营养丰富的培养基中，而只能通过外界入侵才能出现。

===Late heavy bombardment===

The Hadean environment would have been highly hazardous to modern life. Frequent collisions with large objects, up to 500 km in diameter, would have been sufficient to sterilize the planet and vaporize the oceans within a few months of impact, with hot steam mixed with rock vapor becoming high altitude clouds that would completely cover the planet. After a few months, the height of these clouds would have begun to decrease but the cloud base would still have been elevated for about the next thousand years. After that, it would have begun to rain at low altitude. For another two thousand years, rains would slowly have drawn down the height of the clouds, returning the oceans to their original depth only 3,000 y after the impact event.<ref>{{cite journal |last1=Sleep |first1=Norman H. |last2=Zahnle |first2=Kevin J. |authorlink2=Kevin J. Zahnle |last3=Kasting |first3=James F. |last4=Morowitz |first4=Harold J. |authorlink4=Harold J. Morowitz |display-authors=3 |date=9 November 1989 |title=Annihilation of ecosystems by large asteroid impacts on early Earth |journal=Nature |volume=342 |issue=6246|pages=139–142 |url=https://www.researchgate.net/publication/11809063|bibcode=1989Natur.342..139S |doi=10.1038/342139a0 |pmid=11536616|s2cid=1137852 }}</ref>

Louis Pasteur

路易斯 · 巴斯德

Traditionally it was thought that during the period between 4.28<ref name="NAT-20170301" /><ref name="NYT-20170301" /> and 3.8 Gya, changes in the orbits of the [[giant planet]]s may have caused a [[Late Heavy Bombardment|heavy bombardment]] by asteroids and [[comet]]s<ref>{{cite journal |last1=Gomes |first1=Rodney |last2=Levison |first2=Hal F. |authorlink2=Harold F. Levison |last3=Tsiganis |first3=Kleomenis |last4=Morbidelli |first4=Alessandro |authorlink4=Alessandro Morbidelli (astronomer) |date=26 May 2005 |title=Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets |journal=Nature |volume=435 |issue=7041 |pages=466–469 |bibcode=2005Natur.435..466G |doi=10.1038/nature03676 |pmid=15917802|doi-access=free }}</ref> that pockmarked the [[Moon]] and the other inner planets ([[Mercury (planet)|Mercury]], [[Mars]], and presumably Earth and [[Venus]]). This would likely have repeatedly sterilized the planet, had life appeared before that time.<ref name="Follmann2009" /> Geologically, the Hadean Earth would have been far more active than at any other time in its history. Studies of [[meteorite]]s suggests that [[Radionuclide|radioactive isotopes]] such as [[aluminium-26]] with a [[half-life]] of 7.17 ky, and [[potassium-40]] with a half-life of 1.25 Gy, isotopes mainly produced in [[supernova]]e, were much more common.<ref>{{harvnb|Davies|2007|pp=61–73}}</ref> Internal heating as a result of [[Convection#Gravitational or buoyant convection|gravitational sorting]] between the [[Earth core|core]] and the [[Mantle (geology)|mantle]] would have caused a great deal of [[mantle convection]], with the probable result of many more smaller and more active tectonic plates than now exist.

[[Charles Darwin in 1879]]

查尔斯 · 达尔文[1879]

By the middle of the 19th century, biogenesis had accumulated so much evidence in support that the alternative theory of spontaneous generation had been effectively disproven. Pasteur remarked, about a finding of his in 1864 which he considered definitive, <blockquote>Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment. </blockquote>gave a mechanism by which life diversified from a few simple organisms to a variety of to complex forms. Today, scientists agree that all current life descends from earlier life, which has become progressively more complex and diverse through Charles Darwin's mechanism of evolution by natural selection.

到19世纪中叶，生物起源已经积累了如此多的证据来支持自然发生的替代理论已经被有效地推翻。巴斯德谈到他在1864年的一个发现，他认为这个发现是决定性的，他说: 自然发生的学说永远不会从这个简单的实验所造成的致命打击中恢复过来。提供了一种机制，通过这种机制，生命可以从一些简单的有机体变成多种多样的复杂形式。今天，科学家们一致认为，所有现存的生命都是早期生命的延续，通过查尔斯 · 达尔文的自然选择进化机制，早期生命已经变得越来越复杂和多样化。

The time periods between such devastating environmental events give time windows for the possible origin of life in the early environments. If the deep marine hydrothermal setting was the site for the origin of life, then abiogenesis could have happened as early as 4.0-4.2 Gya. If the site was at the surface of the Earth, abiogenesis could only have occurred between 3.7-4.0 Gya.<ref>{{cite journal |last1=Maher |first1=Kevin A. |last2=Stevenson |first2=David J. |date=18 February 1988 |title=Impact frustration of the origin of life |journal=Nature |volume=331 |issue=6157 |pages=612–614 |bibcode=1988Natur.331..612M |doi=10.1038/331612a0 |pmid=11536595|s2cid=4284492 }}</ref>

Darwin wrote to Hooker in 1863 stating that, <blockquote>It is mere rubbish, thinking at present of the origin of life; one might as well think of the origin of matter.</blockquote> In On the Origin of Species, he had referred to life having been "created", by which he "really meant 'appeared' by some wholly unknown process", but had soon regretted using the Old Testament term "creation".

达尔文在1863年写给胡克的信中写道: 这不过是垃圾，目前只考虑生命的起源; 人们不妨考虑物质的起源。在20世纪90年代物种起源，他曾经提到生命是被“创造”的，他的意思是“通过某种完全未知的过程‘出现’” ，但很快就后悔使用了《旧约》中的术语“创造”。

Estimates of the production of organics from these sources suggest that the [[Late Heavy Bombardment]] before 3.5 Ga within the early atmosphere made available quantities of organics comparable to those produced by terrestrial sources.<ref>{{cite journal |last1=Chyba |first1=Christopher |authorlink=Christopher Chyba |last2=Sagan |first2=Carl |authorlink2=Carl Sagan |date=9 January 1992 |title=Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life |journal=Nature |volume=355 |issue=6356 |pages=125–132 |bibcode=1992Natur.355..125C |doi=10.1038/355125a0 |pmid=11538392|s2cid=4346044 }}</ref><ref>{{cite journal |last1=Furukawa |first1=Yoshihiro |last2=Sekine |first2=Toshimori |last3=Oba |first3=Masahiro |last4=Kakegawa |first4=Takeshi |last5=Nakazawa |first5=Hiromoto |display-authors=3 |date=January 2009 |title=Biomolecule formation by oceanic impacts on early Earth |journal=Nature Geoscience |volume=2 |issue=1 |pages=62–66 |bibcode=2009NatGe...2...62F |doi=10.1038/NGEO383}}</ref>

It has been estimated that the Late Heavy Bombardment may also have effectively sterilized the Earth's surface to a depth of tens of meters. If life evolved deeper than this, it would have also been shielded from the early high levels of ultraviolet radiation from the T Tauri stage of the Sun's evolution. Simulations of geothermically heated oceanic crust yield far more organics than those found in the Miller–Urey experiments. In the deep [[hydrothermal vent]]s, Everett Shock has found "there is an enormous thermodynamic drive to form organic compounds, as [[seawater]] and hydrothermal fluids, which are far from equilibrium, mix and move towards a more stable state."<ref>{{harvnb|Davies|1999|p=155}}</ref> Shock has found that the available energy is maximized at around 100–150 C, precisely the temperatures at which the [[Hyperthermophile|hyperthermophilic]] bacteria and [[Thermoacidophile|thermoacidophilic]] [[archaea]] have been found, at the base of the [[Phylogenetic tree|phylogenetic tree of life]] closest to the [[Last universal ancestor|Last Universal Common Ancestor]] (LUCA).<ref>{{harvnb|Bock|Goode|1996}}</ref>

The term biogenesis is usually credited to either Henry Bastian or to Thomas Huxley. Bastian used the term around 1869 in an unpublished exchange with John Tyndall to mean "life-origination or commencement". In 1870, Huxley, as new president of the British Association for the Advancement of Science, delivered an address entitled Biogenesis and Abiogenesis. In it he introduced the term biogenesis (with an opposite meaning to Bastian's) as well as abiogenesis:

生物起源一词通常归功于亨利 · 巴斯蒂安或托马斯 · 赫胥黎。巴斯蒂安在1869年与约翰 · 廷德尔的一次未发表的交流中使用了这个术语，意思是“生命的起源或开始”。在1870年，赫胥黎，作为英国科学协会的新任主席，发表了题为生物起源和自然起源的演讲。在书中，他引入了生物起源这个术语(与巴斯蒂安的意思相反)以及自然起源:

== Earliest evidence of life: palaeontology==

{{Main|Earliest known life forms}}

And thus the hypothesis that living matter always arises by the agency of pre-existing living matter, took definite shape; and had, henceforward, a right to be considered and a claim to be refuted, in each particular case, before the production of living matter in any other way could be admitted by careful reasoners. It will be necessary for me to refer to this hypothesis so frequently, that, to save circumlocution, I shall call it the hypothesis of Biogenesis; and I shall term the contrary doctrine—that living matter may be produced by not living matter—the hypothesis of Abiogenesis. Bastian referred to the possible confusion with Huxley's usage and explicitly renounced his own meaning:

因此，生命物质总是由先前存在的生命物质作用而产生的假设，就成了确定的形式; 从此，在每一个特定的情况下，在以任何其他方式生产生命物质之前，就有权被考虑和要求被驳斥。我必须经常提到这个假说，为了避免拖沓，我将它称为生物起源假说; 我将把这个相反的学说称为自然起源假说，即生物可能是由非生物产生的。巴斯蒂安提到赫胥黎的用法可能会混淆，并明确放弃了他自己的意思:

[[File:Stromatolites.jpg|left|thumb|[[Precambrian]] [[stromatolite]]s in the Siyeh Formation, [[Glacier National Park (U.S.)|Glacier National Park]].

A 2002 study suggested that these 3.5 Gyo (billion year old) [[Geologic formation|formations]] contain fossilized [[cyanobacteria]] [[microorganism|microbes]]. This suggests they are evidence of one of the [[Earliest known life forms|earliest life forms]] on [[Earth]].]]

A word of explanation seems necessary with regard to the introduction of the new term Archebiosis. I had originally, in unpublished writings, adopted the word Biogenesis to express the same meaning—viz., life-origination or commencement. But in the meantime, the word Biogenesis has been made use of, quite independently, by a distinguished biologist [Huxley], who wished to make it bear a totally different meaning. He also introduced the word Abiogenesis. I have been informed, however, on the best authority, that neither of these words can—with any regard to the language from which they are derived—be supposed to bear the meanings which have of late been publicly assigned to them. Wishing to avoid all needless confusion, I therefore renounced the use of the word Biogenesis, and being, for the reason just given, unable to adopt the other term, I was compelled to introduce a new word, in order to designate the process by which living matter is supposed to come into being, independently of pre-existing living matter.

对于新术语“考古学”的引入，一句解释似乎是必要的。在未发表的著作中，我最初用生物起源这个词来表达同样的意思，即生命起源或开始。但与此同时，一位杰出的生物学家[赫胥黎]却相当独立地使用了“生物起源”这个词，他希望赋予它完全不同的含义。他还引入了自然发生这个词。然而，据我所知，这两个词——无论是从哪种语言衍生出来的——都不应该具有近来公开赋予它们的含义。为了避免所有不必要的混乱，我因此放弃使用生物起源这个词，而且由于上述原因，我不能采用另一个词，我不得不引入一个新词，以便指明生命物质应该独立于先前存在的生命物质而产生的过程。

[[File:Stromatolites in Sharkbay.jpg|thumb|Stromatolites in [[Shark Bay]]]]

The earliest life on Earth existed more than 3.5 Gya (billion years ago),<ref name="Origin1" /><ref name="Origin2" /><ref name="RavenJohnson2002" /> during the [[Eoarchean]] Era when sufficient crust had solidified following the molten Hadean Eon. The earliest physical evidence so far found consists of [[Micropaleontology#Microfossils|microfossils]] in the [[Nuvvuagittuq Greenstone Belt]] of Northern Quebec, in [[banded iron formation]] rocks at least 3.77 and possibly 4.28 Gyo.<ref name="NAT-20170301" /><ref>{{cite web |url=http://www.cbc.ca/news/technology/oldest-record-life-earth-found-quebec-1.4004545 |title=Oldest traces of life on Earth found in Quebec, dating back roughly 3.8 Gya |author=Mortillaro, Nicole |publisher=CBC News |date=1 March 2017 |accessdate=2 March 2017 |url-status=live |archiveurl=https://web.archive.org/web/20170301221842/http://www.cbc.ca/news/technology/oldest-record-life-earth-found-quebec-1.4004545 |archivedate=1 March 2017}}</ref> This finding suggested life developed very soon after oceans formed. The structure of the microbes was noted to be similar to bacteria found near [[hydrothermal vents]] in the modern era, and provided support for the hypothesis that abiogenesis began near hydrothermal vents.<ref name="4.3b oldest" /><ref name="NAT-20170301" />

Since the end of the nineteenth century, 'evolutive abiogenesis' means increasing complexity and evolution of matter from inert to living states.

自十九世纪末以来，“进化的自然发生”意味着物质从惰性状态向生命状态的复杂性和进化。

Biogenic [[graphite]] has been found in 3.7 Gyo metasedimentary rocks from southwestern [[Greenland]]<ref name="NG-20131208">{{cite journal |last1=Ohtomo |first1=Yoko |last2=Kakegawa |first2=Takeshi |last3=Ishida |first3=Akizumi |last4=Nagase |first4=Toshiro |last5=Rosing |first5=Minik T. |display-authors=3 |date=January 2014 |title=Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks |journal=[[Nature Geoscience]] |volume=7 |issue=1 |pages=25–28 |bibcode=2014NatGe...7...25O |doi=10.1038/ngeo2025 }}</ref> and [[microbial mat]] fossils found in 3.48 Gyo sandstone from [[Western Australia]].<ref name="AP-20131113">{{cite news |last=Borenstein |first=Seth |date=13 November 2013 |title=Oldest fossil found: Meet your microbial mom |url=http://apnews.excite.com/article/20131113/DAA1VSC01.html |work=[[Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |accessdate=2015-06-02 |url-status=live |archiveurl=https://web.archive.org/web/20150629230719/http://apnews.excite.com/article/20131113/DAA1VSC01.html |archivedate=29 June 2015}}</ref><ref name="AST-20131108">{{cite journal |last1=Noffke |first1=Nora |last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M. |authorlink4=Robert Hazen |date=16 November 2013 |title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ''ca.'' 3.48 Gyo Dresser Formation, Pilbara, Western Australia |journal=[[Astrobiology (journal)|Astrobiology]] |volume=13 |issue=12 |pages=1103–1124 |bibcode=2013AsBio..13.1103N |doi=10.1089/ast.2013.1030 |pmc=3870916 |pmid=24205812}}</ref> Evidence of early life in rocks from [[Akilia]] Island, near the [[Isua Greenstone Belt|Isua supracrustal belt]] in southwestern Greenland, dating to 3.7 Gya have shown biogenic [[carbon isotope]]s.<ref name="NYT-20160831">{{cite news |last=Wade |first=Nicholas |title=World's Oldest Fossils Found in Greenland |url=https://www.nytimes.com/2016/09/01/science/oldest-fossils-on-earth.html |date=31 August 2016 |work=[[The New York Times]] |accessdate=31 August 2016 |url-status=live |archiveurl=https://web.archive.org/web/20160831185959/http://www.nytimes.com/2016/09/01/science/oldest-fossils-on-earth.html |archivedate=31 August 2016}}</ref><ref>{{harvnb|Davies|1999}}</ref> In other parts of the Isua supracrustal belt, graphite inclusions trapped within [[garnet]] crystals are connected to the other elements of life: oxygen, nitrogen, and possibly phosphorus in the form of [[phosphate]], providing further evidence for life 3.7 Gya.<ref>{{Cite journal |last1=Hassenkam|first1=T. |last2=Andersson |first2=M.P. |last3=Dalby|first3=K.N. |last4=Mackenzie |first4=D.M.A.|last5=Rosing |first5=M.T. |title=Elements of Eoarchean life trapped in mineral inclusions |journal=Nature |doi=10.1038/nature23261 |pmid=28738409 |volume=548|issue=7665|pages=78–81 |year=2017 |bibcode=2017Natur.548...78H|s2cid=205257931 }}</ref> At Strelley Pool, in the [[Pilbara]] region of Western Australia, compelling evidence of early life was found in [[pyrite]]-bearing sandstone in a fossilized beach, that showed rounded tubular cells that [[Redox|oxidized]] sulfur by [[photosynthesis]] in the absence of oxygen.<ref name="TG-20131113-JP">{{cite news |last=Pearlman |first=Jonathan |date=13 November 2013 |title=Oldest signs of life on Earth found |url=https://www.telegraph.co.uk/news/science/science-news/10445788/Oldest-signs-of-life-on-Earth-found.html |newspaper=[[The Daily Telegraph]] |location=London |accessdate=2014-12-15 |url-status=live |archiveurl=https://web.archive.org/web/20141216062531/http://www.telegraph.co.uk/news/science/science-news/10445788/Oldest-signs-of-life-on-Earth-found.html |archivedate=16 December 2014}}</ref><ref>{{cite journal |last=O'Donoghue |first=James |date=21 August 2011 |url=https://www.newscientist.com/article/dn20813-oldest-reliable-fossils-show-early-life-was-a-beach.html |title=Oldest reliable fossils show early life was a beach |journal=[[New Scientist]] |url-status=live |archiveurl=https://web.archive.org/web/20150630201918/http://www.newscientist.com/article/dn20813-oldest-reliable-fossils-show-early-life-was-a-beach.html |archivedate=30 June 2015|doi=10.1016/S0262-4079(11)62064-2 |volume=211 |page=13 }}</ref><ref>{{cite journal |last1=Wacey |first1=David |last2=Kilburn |first2=Matt R. |last3=Saunders |first3=Martin |last4=Cliff |first4=John |last5=Brasier |first5=Martin D. |authorlink5=Martin Brasier |display-authors=3 |date=October 2011 |title=Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia |journal=Nature Geoscience |volume=4 |issue=10 |pages=698–702 |bibcode=2011NatGe...4..698W |doi=10.1038/ngeo1238}}</ref> Further research on [[zircon]]s from Western Australia in 2015 suggested that life likely existed on Earth at least 4.1 Gya.<ref name="AP-20151019">{{cite news |last=Borenstein |first=Seth |title=Hints of life on what was thought to be desolate early Earth |url=https://apnews.com/e6be2537b4cd46ffb9c0585bae2b2e51 |date=19 October 2015 |work=AP News |publisher=[[Associated Press]] |accessdate=9 October 2018}}</ref><ref name="PNAS-20151014-pdf">{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnike |first2=Patrick |last3=Harrison |first3=T. Mark |last4=Mao |first4=Wendy L. |display-authors=3 |date=19 October 2015 |title=Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon|journal=Proc. Natl. Acad. Sci. U.S.A. |doi=10.1073/pnas.1517557112|pages=14518–14521 |pmid=26483481 |pmc=4664351 |volume=112 |issue=47 |bibcode=2015PNAS..11214518B}} Early edition, published online before print.</ref><ref name="UCLA-20151019">{{cite web |last1=Wolpert |first1=Stuart |title=Life on Earth likely started at least 4.1 billion years ago – much earlier than scientists had thought |url=http://newsroom.ucla.edu/releases/life-on-earth-likely-started-at-least-4-1-billion-years-ago-much-earlier-than-scientists-had-thought |date=19 October 2015 |publisher=[[ULCA]] |accessdate=20 October 2015 |url-status=live |archiveurl=https://web.archive.org/web/20151020164038/http://newsroom.ucla.edu/releases/life-on-earth-likely-started-at-least-4-1-billion-years-ago-much-earlier-than-scientists-had-thought |archivedate=20 October 2015}}</ref>



< ! ——本节链接自私的基因 >

== Conceptual history until the 1960s: biology ==

=== Panspermia ===

{{Main|Panspermia}}

Panspermia is the [[hypothesis]] that [[life]] exists throughout the [[universe]], distributed by [[meteoroids]], [[asteroids]], [[comets]]<ref name="cometary panspermia">

There is no single generally accepted model for the origin of life. Scientists have proposed several plausible hypotheses which share some common elements. While differing in details, these hypotheses are based on the framework laid out by Alexander Oparin (in 1924) and John Haldane (in 1925), that the first molecules constituting the earliest cells <blockquote>. . . were synthesized under natural conditions by a slow process of molecular evolution, and these molecules then organized into the first molecular system with properties with biological order". </blockquote>Oparin and Haldane suggested that the atmosphere of the early Earth may have been chemically reducing in nature, composed primarily of methane (CH4), ammonia (NH3), water (H2O), hydrogen sulfide (H2S), carbon dioxide (CO2) or carbon monoxide (CO), and phosphate (PO43−), with molecular oxygen (O2) and ozone (O3) either rare or absent. According to later models, the atmosphere in the late Hadean period consisted largely of nitrogen (N2) and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen (H2), and sulfur compounds; while it did lack molecular oxygen and ozone, it was not as chemically reducing as Oparin and Haldane supposed.

对于生命的起源，没有一个公认的单一模型。科学家们提出了几个似是而非的假设，这些假设有一些共同的要素。虽然在细节上有所不同，但这些假设都是基于亚历山大·伊万诺维奇·奥巴林(1924年)和约翰 · 霍尔丹(1925年)提出的框架，即构成最早的细胞的第一个分子。..是在自然条件下通过缓慢的分子进化过程合成的，然后这些分子组织成第一个具有生物序列特性的分子系统”。奥帕林和霍尔丹提出，早期地球的大气可能在本质上是化学还原性的，主要由甲烷(CH 4 )、氨(NH 3 )、水(h 2 o)、硫化氢(h 2 s)组成,二氧化碳(CO 2 )或一氧化碳(CO) ，磷酸盐(PO 4 3-) ，分子氧(o 2 )和臭氧(o 3 )稀少或缺失。根据后来的模型，哈迪恩晚期的大气主要由氮(n 2 )和二氧化碳组成，其中一氧化碳、氢(h 2 )和硫化合物的含量较少，虽然它确实缺乏分子氧和臭氧，但并不像欧帕林和霍尔丹所设想的那样化学还原。

{{cite journal| last=Wickramasinghe|first=Chandra| title=Bacterial morphologies supporting cometary panspermia: a reappraisal| journal=International Journal of Astrobiology|year=2011| volume=10| issue=1| pages=25–30 | doi= 10.1017/S1473550410000157 |bibcode = 2011IJAsB..10...25W|citeseerx=10.1.1.368.4449}}</ref> and [[Small Solar System body|planetoids]].<ref>Rampelotto, P. H. (2010). "Panspermia: A promising field of research". In: Astrobiology Science Conference. Abs 5224.</ref>

No new notable research or hypothesis on the subject appeared until 1924, when Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for life. In his book The Origin of Life, he proposed (echoing Darwin) that the "spontaneous generation of life" that had been attacked by Pasteur did, in fact, occur once, but was now impossible because the conditions found on the early Earth had changed, and preexisting organisms would immediately consume any spontaneously generated organism. Oparin argued that a "primeval soup" of organic molecules could be created in an oxygenless atmosphere through the action of sunlight. These would combine in ever more complex ways until they formed coacervate droplets. These droplets would "grow" by fusion with other droplets, and "reproduce" through fission into daughter droplets, and so have a primitive metabolism in which factors that promote "cell integrity" survive, and those that do not become extinct. Many modern theories of the origin of life still take Oparin's ideas as a starting point.

直到1924年，才出现了关于这个课题的新的值得注意的研究或假设，当时 Oparin 推断大气中的氧气阻止了某些有机化合物的合成，而这些有机化合物是生命必不可少的组成部分。在他的《生命的起源》一书中，他提出(回应达尔文的观点) ，事实上，被巴斯德攻击的“生命自然发生”确实曾经发生过一次，但是现在已经不可能了，因为在早期地球上发现的条件已经发生了变化，先前存在的生物体会立即消耗任何自发生成的生物体。奥帕林认为，有机分子的“原始汤”可以通过阳光的作用在没有氧气的环境中创造出来。这些将以更加复杂的方式结合起来，直到它们形成凝聚的液滴。这些液滴将通过与其他液滴融合而”生长” ，并通过裂变而”繁殖”成子液滴，因此具有原始的新陈代谢，其中促进”细胞完整性”的因素存活下来，而那些没有灭绝的因素则存活下来。许多现代生命起源理论仍然以奥帕林的思想为出发点。

The panspermia hypothesis does not attempt to explain how life first originated but merely shifts the origin to another planet or a comet. The advantage of an extraterrestrial origin of primitive life is that life is not required to have formed on each planet it occurs on, but rather in a single location, and then spread about the [[galaxy]] to other star systems via cometary and/or meteorite impact.<ref name="NYT-20160912">{{cite news |last=Chang |first=Kenneth |title=Visions of Life on Mars in Earth's Depths |url=https://www.nytimes.com/2016/09/13/science/south-african-mine-life-on-mars.html |date=12 September 2016 |work=[[The New York Times]] |accessdate=12 September 2016 |url-status=live |archiveurl=https://web.archive.org/web/20160912225220/http://www.nytimes.com/2016/09/13/science/south-african-mine-life-on-mars.html |archivedate=12 September 2016}}</ref>

About this time, Haldane suggested that the Earth's prebiotic oceans (quite different from their modern counterparts) would have formed a "hot dilute soup" in which organic compounds could have formed. Bernal called this idea biopoiesis or biopoesis, the process of living matter evolving from self-replicating but non-living molecules, and proposed that biopoiesis passes through a number of intermediate stages.

大约在这个时候，霍尔丹提出，地球上生命起源之前的海洋(与现代海洋截然不同)可能形成了一种“热稀释液” ，其中可能形成有机化合物。贝尔纳将这种观点称为生命生成论或生命生成论，即生命物质从自我复制但无生命的分子进化而来的过程，并提出生命生成论要经过若干中间阶段。

Evidence for the panspermia hypothesis is scant, but it finds some support in studies of [[Martian meteorite]]s found in [[Antarctica]] and in studies of [[extremophile]] microbes' survival in outer space tests.<ref>{{cite journal |last=Clark |first=Stuart |date=25 September 2002 |title=Tough Earth bug may be from Mars |url=https://www.newscientist.com/article/dn2844 |journal=New Scientist |accessdate=2015-06-21 |url-status=live |archiveurl=https://web.archive.org/web/20141202003401/http://www.newscientist.com/article/dn2844 |archivedate=2 December 2014}}</ref><ref name="Gerda Horneck">{{cite journal |last1=Horneck |first1=Gerda |last2=Klaus |first2=David M. |last3=Mancinelli |first3=Rocco L. |date=March 2010 |title=Space Microbiology |journal=[[Microbiology and Molecular Biology Reviews]] |volume=74 |issue=1 |pages=121–156 |doi=10.1128/MMBR.00016-09 |pmc=2832349 |pmid=20197502|bibcode=2010MMBR...74..121H }}</ref><ref name="Rabbow">{{cite journal |last1=Rabbow |first1=Elke |last2=Horneck |first2=Gerda |last3=Rettberg |first3=Petra |last4=Schott |first4=Jobst-Ulrich |last5=Panitz |first5=Corinna |last6=L'Afflitto |first6=Andrea |last7=von Heise-Rotenburg |first7=Ralf |last8=Willnecker |first8=Reiner |last9=Baglioni |first9=Pietro |last10=Hatton |first10=Jason |last11=Dettmann |first11=Jan |last12=Demets |first12=René |last13=Reitz |first13=Günther |display-authors=3 |date=December 2009 |title=EXPOSE, an Astrobiological Exposure Facility on the International Space Station – from Proposal to Flight |journal=Origins of Life and Evolution of Biospheres |volume=39 |issue=6 |pages=581–598 |bibcode=2009OLEB...39..581R |doi=10.1007/s11084-009-9173-6|pmid=19629743|s2cid=19749414 }}</ref><ref>{{cite journal |last1=Onofri |first1=Silvano |last2=de la Torre |first2=Rosa |last3=de Vera |first3=Jean-Pierre |last4=Ott |first4=Sieglinde |last5=Zucconi |first5=Laura |last6=Selbmann |first6=Laura |last7=Scalzi |first7=Giuliano |last8=Venkateswaran |first8=Kasthuri J. |last9=Rabbow |first9=Elke |last10=Sánchez Iñigo |first10=Francisco J. |last11=Horneck |first11=Gerda |display-authors=3 |date=May 2012 |title=Survival of Rock-Colonizing Organisms After 1.5 Years in Outer Space |journal=Astrobiology |volume=12 |issue=5 |pages=508–516 |bibcode=2012AsBio..12..508O |doi=10.1089/ast.2011.0736 |pmid=22680696}}</ref>

Robert Shapiro has summarized the "primordial soup" theory of Oparin and Haldane in its "mature form" as follows:

罗伯特•夏皮罗(Robert Shapiro)将 Oparin 和霍尔丹的“原始汤”理论以“成熟形式”概括如下:

In August 2020, scientists reported that [[bacteria]] from Earth, particularly ''[[Deinococcus radiodurans]]'', which is highly resistant to [[environmental hazard]]s, were found to survive for three years in [[outer space]], based on studies conducted on the [[International Space Station]].<ref name="CNN-20200826">{{cite news |last=Strickland |first=Ashley |title=Bacteria from Earth can survive in space and could endure the trip to Mars, according to new study |url=https://www.cnn.com/2020/08/26/world/earth-mars-bacteria-space-scn/index.html |date=26 August 2020 |work=[[CNN News]] |accessdate=26 August 2020 }}</ref><ref name="FM-20200826">{{cite journal |author=Kawaguchi, Yuko |display-authors=et al. |title=DNA Damage and Survival Time Course of Deinococcal Cell Pellets During 3 Years of Exposure to Outer Space |date=26 August 2020 |journal=[[Frontiers in Microbiology]] |volume=11 |page=2050 |doi=10.3389/fmicb.2020.02050 |pmid=32983036 |pmc=7479814 |s2cid=221300151 |doi-access=free }}</ref>

The early Earth had a chemically reducing atmosphere.

早期的地球有一个化学还原大气层。

This atmosphere, exposed to energy in various forms, produced simple organic compounds ("monomers").

这种大气暴露在各种形式的能量下，产生简单的有机化合物(“单体”)。

====Origin of life posited directly after the Big Bang and have spread over the entire Universe====

These compounds accumulated in a "soup" that may have concentrated at various locations (shorelines, oceanic vents etc.).

这些化合物聚集在一个“汤”中，可能集中在不同的地点(海岸线、海底喷口等)。).

An extreme speculation is that the [[biochemistry]] of life could have begun as early as 17 My (million years) after the [[Big Bang]], during a [[Chronology of the universe#Speculative "habitable epoch"|habitable epoch]], and that life may exist throughout the [[universe]].<ref name="IJA-2014October_ARXIV-20131202">{{cite journal|last=Loeb|first=Abraham|authorlink=Abraham (Avi) Loeb|date=2014|title=The habitable epoch of the early universe|journal=[[International Journal of Astrobiology]]|volume=13|issue=4|pages=337–339|arxiv=1312.0613|bibcode=2014IJAsB..13..337L|citeseerx=10.1.1.748.4820|doi=10.1017/S1473550414000196|s2cid=2777386}}</ref><ref name="NYT-20141202">{{cite news|url=https://www.nytimes.com/2014/12/02/science/avi-loeb-ponders-the-early-universe-nature-and-life.html|title=Much-Discussed Views That Go Way Back|last=Dreifus|first=Claudia|date=2 December 2014|newspaper=[[The New York Times]]|accessdate=2014-12-03|archiveurl=https://web.archive.org/web/20141203010758/http://www.nytimes.com/2014/12/02/science/avi-loeb-ponders-the-early-universe-nature-and-life.html|archivedate=3 December 2014|url-status=live|location=New York|page=D2|authorlink=Claudia Dreifus}}</ref>

By further transformation, more complex organic polymers—and ultimately life—developed in the soup.

通过进一步的转化，更复杂的有机聚合物——以及最终的生命——在汤中发展起来。

====Panspermia by life brought from Mars to Earth====

Carl Zimmer has speculated that the chemical conditions, including the presence of [[boron]], [[molybdenum]] and oxygen needed for the initial production of RNA, may have been better on early Mars than on early Earth.<ref name="NYT-20130912">{{cite news |last=Zimmer |first=Carl |date=12 September 2013 |title=A Far-Flung Possibility for the Origin of Life |url=https://www.nytimes.com/2013/09/12/science/space/a-far-flung-possibility-for-the-origin-of-life.html |newspaper=The New York Times |location=New York |accessdate=2015-06-15 |url-status=live |archiveurl=https://web.archive.org/web/20150708122622/http://www.nytimes.com/2013/09/12/science/space/a-far-flung-possibility-for-the-origin-of-life.html |archivedate=8 July 2015}}</ref><ref name="NS-20130829">{{cite journal |last=Webb |first=Richard |date=29 August 2013 |title=Primordial broth of life was a dry Martian cup-a-soup |url=https://www.newscientist.com/article/dn24120-primordial-broth-of-life-was-a-dry-martian-cupasoup.html |journal=New Scientist |accessdate=2015-06-16 |url-status=live |archiveurl=https://web.archive.org/web/20150424181341/http://www.newscientist.com/article/dn24120-primordial-broth-of-life-was-a-dry-martian-cupasoup.html |archivedate=24 April 2015}}</ref><ref>{{cite journal |author1=Wentao Ma |author2=Chunwu Yu |author3=Wentao Zhang |author4=Jiming Hu |display-authors=3 |date=November 2007 |title=Nucleotide synthetase ribozymes may have emerged first in the RNA world |journal=[[RNA (journal)|RNA]] |volume=13 |issue=11 |pages=2012–2019 |doi=10.1261/rna.658507 |pmc=2040096 |pmid=17878321}}</ref> If so, life-suitable molecules originating on Mars may have later migrated to Earth via [[Impact event|meteor ejections]].

John Bernal showed that based upon this and subsequent work there is no difficulty in principle in forming most of the molecules we recognize as the necessary molecules for life from their inorganic precursors. The underlying hypothesis held by Oparin, Haldane, Bernal, Miller and Urey, for instance, was that multiple conditions on the primeval Earth favoured chemical reactions that synthesized the same set of complex organic compounds from such simple precursors.

约翰 · 伯纳尔指出，基于这项工作和随后的工作，在原则上形成大多数我们认为是生命所必需的分子的无机前体是没有困难的。例如，Oparin，Haldane，Bernal，Miller 和 Urey 所持有的基本假设是，原始地球上的多种条件有利于化学反应，从这些简单的前体合成同一套复杂的有机化合物。

Bernal coined the term biopoiesis in 1949 to refer to the origin of life. In 1967, he suggested that it occurred in three "stages":

伯纳尔在1949年创造了生命生成这个术语来指代生命的起源。1967年，他提出，这一过程分为三个“阶段” :

=== Spontaneous generation ===

====General acceptance of spontaneous generation until the 19th century====

the origin of biological monomers

生物单体的起源

{{Main|Spontaneous generation}}

the origin of biological polymers

生物聚合物的起源

Traditional religion attributed the origin of life to supernatural deities who created the natural world. ''Spontaneous generation,'' the first naturalistic theory of life arising from non-life, goes back to [[Aristotle]] and [[ancient Greek philosophy]], and continued to have support in Western scholarship until the 19th century.<ref>{{harvnb|Sheldon|2005}}</ref> Classical notions of spontaneous generation held that certain "lower" or "vermin" animals are generated by decaying organic substances. According to Aristotle, it was readily observable that [[aphid]]s arise from dew on plants, [[fly|flies]] from putrid matter, mice from dirty hay, crocodiles from rotting sunken logs, and so on.<ref>{{harvnb|Lennox|2001|pp=229–258}}</ref> A related theory was ''heterogenesis'': that some forms of life could arise from different forms (e.g. bees from flowers).<ref>{{harvnb|Vartanian|1973|pp=307–312}}</ref> The modern scientist [[John Desmond Bernal|John Bernal]] said that the basic idea of such theories was that life was continuously created as a result of chance events.<ref name="Bernal 1967">{{harvnb|Bernal|1967}}</ref>

the evolution from molecules to cells

从分子到细胞的进化过程

In the 17th century, people began to question such assumptions. In 1646, [[Sir Thomas Browne|Thomas Browne]] published his ''[[Pseudodoxia Epidemica]]'' (subtitled ''Enquiries into Very many Received Tenets, and commonly Presumed Truths''), which was an attack on false beliefs and "vulgar errors." His contemporary, [[Alexander Ross (writer)|Alexander Ross]], erroneously refuted him, stating:<blockquote> To question this [spontaneous generation], is to question Reason, Sense, and Experience: If he doubts of this, let him go to ''[[Egypt|Ægypt]]'', and there he will find the fields swarming with mice begot of the mud of ''[[Nile|Nylus]]'', to the great calamity of the Inhabitants.<ref>{{cite journal |last=Balme |first=D.M. |authorlink=David Mowbray Balme |year=1962 |title=Development of Biology in Aristotle and Theophrastus: Theory of Spontaneous Generation |journal=[[Phronesis (journal)|Phronesis]] |volume=7 |issue=1–2 |pages=91–104 |doi=10.1163/156852862X00052}}</ref><ref>{{harvnb|Ross|1652}}</ref></blockquote>

Bernal suggested that evolution commenced between stages 1 and 2. Bernal regarded the third stage, in which biological reactions were incorporated behind a cell's boundary, as the most difficult. Modern work on the way that cell membranes self-assemble, and the work on micropores in various substrates, may be a key step towards understanding the development of independent free-living cells.

贝尔纳认为进化始于第一阶段和第二阶段。贝尔纳认为第三阶段是最困难的阶段，在这个阶段中，生物反应在细胞边界之后合并起来。细胞膜自我组装的方式以及对不同基质中微孔的研究，可能是理解独立自由生活细胞发展的关键一步。

[[File:Anton van Leeuwenhoek.png|thumb|upright|Antonie van Leeuwenhoek]]

In 1665, [[Robert Hooke]] published the first drawings of a [[microorganism]]. Hooke was followed in 1676 by [[Antonie van Leeuwenhoek]], who drew and described microorganisms that are now thought to have been [[protozoa]] and [[bacteria]].<ref>{{harvnb|Dobell|1960}}</ref> Many felt the existence of microorganisms was evidence in support of spontaneous generation, since microorganisms seemed too simplistic for [[sexual reproduction]], and [[asexual reproduction]] through [[mitosis|cell division]] had not yet been observed. Van Leeuwenhoek took issue with the ideas common at the time that fleas and lice could spontaneously result from [[putrefaction]], and that frogs could likewise arise from slime. Using a broad range of experiments ranging from sealed and open meat incubation and the close study of insect reproduction he became, by the 1680s, convinced that spontaneous generation was incorrect.<ref>{{harvnb|Bondeson|1999}}</ref>

Stanley Miller

斯坦利 · 米勒

Miller–Urey experiment JP One of the most important pieces of experimental support for the "soup" theory came in 1952. Stanley Miller and Harold Urey performed an experiment that demonstrated how organic molecules could have spontaneously formed from inorganic precursors under conditions like those posited by the Oparin-Haldane hypothesis. The now-famous Miller–Urey experiment used a highly reducing mixture of gases—methane, ammonia, and hydrogen, as well as water vapor—to form simple organic monomers such as amino acids. The mixture of gases was cycled through an apparatus that delivered electrical sparks to the mixture. After one week, it was found that about 10% to 15% of the carbon in the system was then in the form of a racemic mixture of organic compounds, including amino acids, which are the building blocks of proteins. This provided direct experimental support for the second point of the "soup" theory, and it is around the remaining two points of the theory that much of the debate now centers.

米勒-尤里实验 JP 对“汤”理论最重要的实验支持来自1952年。斯坦利 · 米勒和哈罗德 · 尤里进行了一项实验，证明了有机分子是如何在像奥帕林-霍尔丹假说所假设的条件下从无机前体自发形成的。现在著名的 Miller-Urey 实验利用甲烷、氨、氢以及水蒸气的高还原性混合气体，形成简单的有机单体，如氨基酸。气体混合物通过一个装置循环输送电火花到混合物中。一个星期后，发现系统中大约10% 到15% 的碳是以外消旋的有机化合物混合物的形式存在的，包括氨基酸，氨基酸是蛋白质的组成单元。这为“汤”理论的第二个观点提供了直接的实验支持，并且围绕该理论的其余两个观点进行了大量的争论。

The first experimental evidence against spontaneous generation came in 1668 when [[Francesco Redi]] showed that no [[maggot]]s appeared in meat when flies were prevented from laying eggs. It was gradually shown that, at least in the case of all the higher and readily visible organisms, the previous sentiment regarding spontaneous generation was false. The alternative hypothesis was ''[[biogenesis]]'': that every living thing came from a pre-existing living thing (''omne vivum ex ovo'', Latin for "every living thing from an egg").<ref name=lev>{{cite web |vauthors=Levine R, Evers C |title=The Slow Death of Spontaneous Generation (1668-1859) |url=http://www.accessexcellence.org/RC/AB/BC/Spontaneous_Generation.php |accessdate=18 April 2013 |url-status=dead |archiveurl=https://web.archive.org/web/20080426191204/http://www.accessexcellence.org/RC/AB/BC/Spontaneous_Generation.php |archivedate=26 April 2008 }}</ref> In 1768, [[Lazzaro Spallanzani]] demonstrated that [[microorganism|microbes]] were present in the air, and could be killed by boiling. In 1861, [[Louis Pasteur]] performed a series of experiments that demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media, but could only appear by invasion from without.

A 2011 reanalysis of the saved vials containing the original extracts that resulted from the Miller and Urey experiments, using current and more advanced analytical equipment and technology, has uncovered more biochemicals than originally discovered in the 1950s. One of the more important findings was 23 amino acids, far more than the five originally found.

2011年对保存下来的小瓶进行了重新分析，其中包含了 Miller 和 Urey 实验的原始提取物，使用了当前更先进的分析设备和技术，发现了比20世纪50年代最初发现的更多的生化物质。其中一个更重要的发现是23种氨基酸，远远超过最初发现的5种。

====Spontaneous generation considered disproven in the 19th century====

[[File:Louis Pasteur, foto av Paul Nadar, Crisco edit.jpg|thumb|upright|left|Louis Pasteur]]

The chemical processes on the pre-biotic early Earth are called chemical evolution.

前生命早期地球上的化学过程称为化学演化。

[[File:Darwin restored2.jpg|thumb|upright|alt=Head and shoulders portrait, increasingly bald with rather uneven bushy white eyebrows and beard, his wrinkled forehead suggesting a puzzled frown|[[Charles Darwin]] in 1879]]

The elements, except for hydrogen and helium, ultimately derive from stellar nucleosynthesis. In 2016, astronomers reported that the very basic chemical ingredients of life—the carbon-hydrogen molecule (CH, or methylidyne radical), the carbon-hydrogen positive ion (CH+) and the carbon ion (C+)—are largely the result of ultraviolet light from stars, rather than other forms of radiation from supernovae and young stars, as thought earlier. Complex molecules, including organic molecules, form naturally both in space and on planets. (See pseudo-panspermia)

这些元素，除了氢和氦，最终都来自恆星核合成。2016年，天文学家报告说，生命中最基本的化学成分---- 碳氢分子(CH，或甲炔)、碳氢阳离子(CH +)和碳离子(c +)---- 大部分是恒星紫外线的结果，而不是之前认为的超新星和年轻恒星的其他形式的辐射。复杂的分子，包括有机分子，在太空和行星上都会自然形成。(见伪胚种论)

By the middle of the 19th century, biogenesis had accumulated so much evidence in support that the alternative theory of spontaneous generation had been effectively disproven. [[Louis Pasteur|Pasteur]] remarked, about a finding of his in 1864 which he considered definitive, <blockquote>Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.<ref>{{harvnb|Oparin|1953|p=196}}</ref><ref name="Tyndall Fragments2">{{harvnb|Tyndall|1905|loc=IV, XII (1876), XIII (1878)}}</ref> </blockquote>gave a mechanism by which life diversified from a few simple organisms to a variety of to complex forms. Today, scientists agree that all current life descends from earlier life, which has become progressively more complex and diverse through [[Charles Darwin]]'s mechanism of [[evolution]] by [[natural selection]].

Darwin wrote to Hooker in 1863 stating that, <blockquote>It is mere rubbish, thinking at present of the origin of life; one might as well think of the origin of matter.</blockquote> In ''[[On the Origin of Species]]'', he had referred to life having been "created", by which he "really meant 'appeared' by some wholly unknown process", but had soon regretted using the Old Testament term "creation".{{Citation needed|date=July 2020}}

An organic compound is any member of a large class of gaseous, liquid, or solid chemicals whose molecules contain carbon. Carbon is the fourth most abundant element in the Universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Organic compounds are relatively common in space, formed by "factories of complex molecular synthesis" which occur in molecular clouds and circumstellar envelopes, and chemically evolve after reactions are initiated mostly by ionizing radiation. Based on computer model studies, the complex organic molecules necessary for life may have formed on dust grains in the protoplanetary disk surrounding the Sun before the formation of the Earth.</blockquote> Comets are encrusted with outer layers of dark material, thought to be a tar-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by ionizing radiation. It is possible that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth. Amino acids which were formed extraterrestrially may also have arrived on Earth via comets.

有机化合物是一大类气体、液体或固体化学物质中的任何成员，其分子中含有碳。碳是宇宙中质量第四丰富的元素，仅次于氢、氦和氧。太阳、恒星、彗星以及大多数行星的大气中都含有大量的碳。有机化合物在太空中相对普遍，由分子云和环恒星包膜中的“复杂分子合成工厂”形成，化学进化在反应后主要由电离辐射引发。根据计算机模型研究，在地球形成之前，生命所必需的复杂有机分子可能已经在环绕太阳的原行星盘中的尘埃颗粒上形成。彗星外面包裹着一层黑色物质，这种物质被认为是焦油状的物质，由简单的碳化合物经过主要由电离辐射引发的反应形成的复杂有机物质组成。来自彗星的物质雨可能会给地球带来大量这种复杂的有机分子。外星人形成的氨基酸也可能是通过彗星到达地球的。

==== Etymology of biogenesis and abiogenesis====



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The [[Cat's Paw Nebula lies inside the Milky Way Galaxy and is located in the constellation Scorpius. Green areas show regions where radiation from hot stars collided with large molecules and small dust grains called "polycyclic aromatic hydrocarbons" (PAHs), causing them to fluoresce. (Spitzer space telescope, 2018)]]

猫爪星云位于银河系内，位于 Scorpius 星座。绿色区域显示了来自炽热恒星的辐射与被称为“多环芳烃”(PAHs)的大分子和小尘埃颗粒相撞的区域，使它们发出荧光。[斯皮策空间望远镜，2018]]

Subsequently, in the preface to Bastian's 1871 book, ''The Modes of Origin of Lowest Organisms'',<ref>{{harvnb|Bastian|1871}}</ref> Bastian referred to the possible confusion with Huxley's usage and explicitly renounced his own meaning:

Polycyclic aromatic hydrocarbons (PAH) are known to be abundant in the universe, including in the interstellar medium, in comets, and in meteorites, and are some of the most complex molecules so far found in space. In 2010, another team also detected PAHs, along with fullerenes, in nebulae. The Spitzer Space Telescope has detected a star, HH 46-IR, which is forming by a process similar to that by which the Sun formed. In the disk of material surrounding the star, there is a very large range of molecules, including cyanide compounds, hydrocarbons, and carbon monoxide. In 2012, NASA scientists reported that PAHs, subjected to interstellar medium conditions, are transformed, through hydrogenation, oxygenation and hydroxylation, to more complex organics—"a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively." Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks." More than 20% of the carbon in the universe may be associated with PAHs, Studies reported in 2008, based on 12C/13C isotopic ratios of organic compounds found in the Murchison meteorite, suggested that the RNA component uracil and related molecules, including xanthine, were formed extraterrestrially. In 2011, a report based on NASA studies of meteorites found on Earth was published suggesting DNA components (adenine, guanine and related organic molecules) were made in outer space. Scientists also found that the cosmic dust permeating the universe contains complex organics ("amorphous organic solids with a mixed aromatic–aliphatic structure") that could be created naturally, and rapidly, by stars. Sun Kwok of The University of Hong Kong suggested that these compounds may have been related to the development of life on Earth said that "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life." In 2012, Jørgensen's team reported the detection of glycolaldehyde in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422 400 light years from Earth. Glycolaldehyde is needed to form RNA, which is similar in function to DNA. These findings suggest that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation. Because sugars are associated with both metabolism and the genetic code, two of the most basic aspects of life, it is thought the discovery of extraterrestrial sugar increases the likelihood that life may exist elsewhere in our galaxy. Polyphosphates are formed by polymerization of ordinary monophosphate ions PO43-. Several mechanisms of organic molecule synthesis have been investigated. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as adenosine triphosphate (ATP). A key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate (apatite), so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth.

众所周知，宇宙中含有丰富的多环芳烃，包括星际物质、彗星和陨石，是迄今为止在太空中发现的最复杂的分子之一。2010年，另一个研究小组也在星云中检测到了多环芳烃和富勒烯。斯皮策空间望远镜天文台探测到了一颗恒星，HH 46-IR，它的形成过程与太阳形成的过程相似。在这颗恒星周围的物质盘中，存在着大量的分子，包括氰化物、碳氢化合物和一氧化碳。2012年，美国宇航局的科学家报告说，在星际物质条件下，多环芳烃通过氢化、氧化和羟化转化为更复杂的有机物ーー“分别朝着蛋白质和 DNA 的原料氨基酸和核苷酸的方向迈进了一步。”此外，由于这些转变的结果，多环芳烃失去了它们的光谱特征，这可能是“在星际冰颗粒中，特别是在冷的、稠密的云层的外部区域或原行星盘的高分子层中，多环芳烃检测不到的原因之一。”根据2008年的研究报告，宇宙中超过20% 的碳可能与多环芳烃有关，根据默奇森陨石中发现的有机化合物的 c 同位素比值，表明 RNA 成分尿嘧啶和相关分子，包括黄嘌呤，是外星人形成的。2011年，一份基于美国宇航局对地球上发现的陨石的研究报告发表，报告称外层空间制造了 DNA 成分(腺嘌呤、鸟嘌呤和相关的有机分子)。科学家们还发现，宇宙尘埃中充斥着复杂的有机物(“具有混合芳香-脂肪结构的无定形有机固体”) ，这些物质可以由恒星自然而迅速地产生。香港大学的 Sun Kwok 认为这些化合物可能与地球上生命的发展有关，他说: “如果是这样的话，地球上的生命可能更容易开始，因为这些有机物可以作为生命的基本成分。”2012年，j ø rgensen 的团队报告了在一个遥远的恒星系统中发现乙醇醛的情况。这个分子是在距离地球400光年的原恒星双星 IRAS 16293-2422附近发现的。乙醇醛是形成 RNA 的必需物质，其功能与 DNA 相似。这些发现表明，在行星形成之前，复杂的有机分子可能在恒星系统中形成，最终在年轻行星形成的早期到达。因为糖同时与新陈代谢和遗传密码有关---- 这是生命最基本的两个方面---- 人们认为外星糖的发现增加了银河系其他地方存在生命的可能性。聚磷酸盐是由普通单磷酸盐离子 PO 4 3- 聚合而成。研究了有机分子合成的几种机理。多聚磷酸盐引起氨基酸聚合成肽。它们也是合成三磷酸腺苷(ATP)等关键生化化合物的逻辑前体。一个关键问题似乎是钙与可溶性磷酸盐反应生成不溶性磷酸钙(磷灰石) ，因此必须找到一些合理的机制来防止钙离子导致磷酸盐的沉淀。这些年来在这个问题上已经做了很多工作，但是一个有趣的新想法是，陨石可能已经在地球早期引入了活性磷物质。

Based on recent computer model studies, the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth. According to the computer studies, this same process may also occur around other stars that acquire planets. (Also see Extraterrestrial organic molecules).

根据最近的计算机模型研究，在地球形成之前，生命所必需的复杂有机分子可能已经在太阳周围的原行星盘中形成了。根据计算机研究，同样的过程也可能发生在获得行星的其他恒星周围。(还可以看到外星有机分子)。

:A word of explanation seems necessary with regard to the introduction of the new term ''Archebiosis''. I had originally, in unpublished writings, adopted the word ''Biogenesis'' to express the same meaning—viz., life-origination or commencement. But in the meantime, the word ''Biogenesis'' has been made use of, quite independently, by a distinguished biologist [Huxley], who wished to make it bear a totally different meaning. He also introduced the word ''Abiogenesis''. I have been informed, however, on the best authority, that neither of these words can—with any regard to the language from which they are derived—be supposed to bear the meanings which have of late been publicly assigned to them. Wishing to avoid all needless confusion, I therefore renounced the use of the word ''Biogenesis'', and being, for the reason just given, unable to adopt the other term, I was compelled to introduce a new word, in order to designate the process by which living matter is supposed to come into being, independently of pre-existing living matter.<ref>{{harvnb|Bastian|1871|p=[https://ia902701.us.archive.org/BookReader/BookReaderImages.php?zip=/23/items/modesoforiginofl00bast/modesoforiginofl00bast_jp2.zip&file=modesoforiginofl00bast_jp2/modesoforiginofl00bast_0015.jp2&scale=4&rotate=0 xi–xii]}}</ref>

The accumulation and concentration of organic molecules on a planetary surface is also considered an essential early step for the origin of life. Although HCN is poisonous, it only affects aerobic organisms (eukaryotes and aerobic bacteria), which did not yet exist. It can play roles in other chemical processes as well, such as the synthesis of the amino acid glycine. A group of Czech scientists reported that all four RNA-bases may be synthesized from formamide in the course of high-energy density events like extraterrestrial impacts.

有机分子在行星表面的积累和集中也被认为是生命起源的必要的早期步骤。尽管 HCN 是有毒的，但它只影响需氧生物(真核生物和需氧细菌) ，而这些生物还不存在。它也可以在其他化学过程中发挥作用，如氨基酸甘氨酸的合成。一组捷克科学家报告说，所有四个 rna 碱基可能合成的甲酰胺在高能量密度事件的过程中，如外星撞击。

Since the end of the nineteenth century, 'evolutive abiogenesis' means increasing complexity and evolution of matter from inert to living states.<ref>[https://link.springer.com/referenceworkentry/10.1007/978-3-642-27833-4_2-4 Abiogenesis – Definition]. 20 April 2015. ''Encyclopedia of Astrobiology''. {{doi|10.1007/978-3-642-27833-4_2-4}}</ref>

=== Oparin: Primordial soup hypothesis ===

In 1961, it was shown that the nucleic acid purine base adenine can be formed by heating aqueous ammonium cyanide solutions.

1961年，人们发现通过加热氰化铵水溶液可以形成核酸嘌呤碱腺嘌呤。

{{anchor | Haldane and Oparin: The Primordial Soup Theory}}

{{Main|Primordial soup}}

{{further|Miller–Urey experiment}}

Other pathways for synthesizing bases from inorganic materials were also reported. Orgel and colleagues have shown that freezing temperatures are advantageous for the synthesis of purines, due to the concentrating effect for key precursors such as hydrogen cyanide. Research by Miller and colleagues suggested that while adenine and guanine require freezing conditions for synthesis, cytosine and uracil may require boiling temperatures. Research by the Miller group notes the formation of seven different amino acids and 11 types of nucleobases in ice when ammonia and cyanide were left in a freezer from 1972 to 1997. Other work demonstrated the formation of s-triazines (alternative nucleobases), pyrimidines (including cytosine and uracil), and adenine from urea solutions subjected to freeze-thaw cycles under a reductive atmosphere (with spark discharges as an energy source). The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing. As an ice crystal forms, it stays pure: only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often. Mechanistic exploration using quantum chemical methods provide a more detailed understanding of some of the chemical processes involved in chemical evolution, and a partial answer to the fundamental question of molecular biogenesis.

其他途径合成碱从无机材料也报道。和他的同事们已经证明，冷冻温度对于合成嘌呤是有利的，因为它对于关键的前体物质如氰化氢具有浓缩作用。米勒及其同事的研究表明，腺嘌呤和鸟嘌呤的合成需要冷冻条件，而胞嘧啶和尿嘧啶可能需要沸腾的温度。米勒小组的研究指出，从1972年到1997年，氨和氰化物被置于冰箱中，在冰中形成了7种不同的氨基酸和11种碱基。其他工作证明了在还原气氛下(以火花放电为能源) ，尿素溶液经冻融循环后形成 s- 三嗪(交替核酸碱基)、嘧啶(包括胞嘧啶和尿嘧啶)和腺嘌呤。在如此低的温度下，这些反应的不寻常速度的解释是共晶凝固。当冰晶形成时，它保持纯净: 只有水分子加入生长中的晶体，而像盐或氰化物这样的杂质被排除。这些杂质聚集在冰中的微小液囊中，这种聚集导致分子更频繁地碰撞。利用量子化学方法进行的机械探索提供了对化学进化所涉及的一些化学过程的更详细的理解，并对分子生物起源的基本问题作出了部分的回答。

There is no single generally accepted model for the origin of life. Scientists have proposed several plausible hypotheses which share some common elements. While differing in details, these hypotheses are based on the framework laid out by [[Alexander Oparin]] (in 1924) and [[J. B. S. Haldane|John Haldane]] (in 1925), that the first molecules constituting the earliest cells <blockquote>. . . were synthesized under natural conditions by a slow process of molecular evolution, and these molecules then organized into the first molecular system with properties with biological order".<ref name="bah2">{{cite journal|last=Bahadur|first=Krishna|year=1973|title=Photochemical Formation of Self–sustaining Coacervates|url=http://www.dli.gov.in/rawdataupload/upload/insa/INSA_1/20005b73_455.pdf|url-status=dead|journal=Proceedings of the Indian National Science Academy|volume=39B|issue=4|pages=455–467|doi=10.1016/S0044-4057(75)80076-1|pmid=1242552|archiveurl=https://web.archive.org/web/20131019172800/http://www.dli.gov.in/rawdataupload/upload/insa/INSA_1/20005b73_455.pdf|archivedate=19 October 2013}}

* {{cite journal|last=Bahadur|first=Krishna|year=1975|title=Photochemical Formation of Self-Sustaining Coacervates|journal=[[Microbiological Research|Zentralblatt für Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene]]|volume=130|issue=3|pages=211–218|doi=10.1016/S0044-4057(75)80076-1|oclc=641018092|pmid=1242552}}</ref> </blockquote>Oparin and Haldane suggested that the atmosphere of the early Earth may have been chemically reducing in nature, composed primarily of methane (CH4), ammonia (NH3), water (H2O), hydrogen sulfide (H2S), carbon dioxide (CO2) or carbon monoxide (CO), and [[phosphate]] (PO43−), with molecular oxygen (O2) and [[ozone]] (O3) either rare or absent. According to later models, the atmosphere in the late Hadean period consisted largely of nitrogen (N2) and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen (H2), and sulfur compounds;<ref>{{harvnb|Kasting|1993|p=922}}</ref> while it did lack molecular oxygen and ozone,<ref>{{harvnb|Kasting|1993|p=920}}</ref> it was not as chemically reducing as Oparin and Haldane supposed.

At the time of the Miller–Urey experiment, scientific consensus was that the early Earth had a reducing atmosphere with compounds relatively rich in hydrogen and poor in oxygen (e.g., CH4 and NH3 as opposed to CO2 and nitrogen dioxide (NO2)). However, current scientific consensus describes the primitive atmosphere as either weakly reducing or neutral (see also Oxygen Catastrophe). Such an atmosphere would diminish both the amount and variety of amino acids that could be produced, although studies that include iron and carbonate minerals (thought present in early oceans) in the experimental conditions have again produced a diverse array of amino acids.

在进行 Miller-Urey 实验时，科学界一致认为，早期地球的还原大气中氢含量较高，氧含量较低(如 CH 4 和 NH 3 相对于 CO 2 和二氧化氮(NO 2 ))。然而，目前的科学共识将原始大气描述为弱还原或中性(参见氧灾难)。这种气氛会减少可以产生的氨基酸的数量和种类，尽管在实验条件下包括铁和碳酸盐矿物质(认为存在于早期海洋中)的研究再次产生了各种各样的氨基酸。

No new notable research or hypothesis on the subject appeared until 1924, when Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for life. In his book ''The Origin of Life'',<ref>{{harvnb|Bernal|1967|loc=[http://www.valencia.edu/~orilife/textos/The%20Origin%20of%20Life.pdf ''The Origin of Life'' (A.I. Oparin, 1924), pp. 199–234]}}</ref><ref>{{harvnb|Oparin|1953}}</ref> he proposed (echoing Darwin) that the "spontaneous generation of life" that had been attacked by Pasteur did, in fact, occur once, but was now impossible because the conditions found on the early Earth had changed, and preexisting organisms would immediately consume any spontaneously generated organism. Oparin argued that a "primeval soup" of organic molecules could be created in an oxygenless atmosphere through the action of [[sunlight]]. These would combine in ever more complex ways until they formed [[coacervate]] droplets. These droplets would "[[cell growth|grow]]" by fusion with other droplets, and "[[reproduction|reproduce]]" through fission into daughter droplets, and so have a primitive [[metabolism]] in which factors that promote "cell integrity" survive, and those that do not become [[Extinction|extinct]]. Many modern theories of the origin of life still take Oparin's ideas as a starting point.

About this time, Haldane suggested that the Earth's prebiotic oceans (quite different from their modern counterparts) would have formed a "hot dilute soup" in which organic compounds could have formed. Bernal called this idea ''biopoiesis'' or ''biopoesis'', the process of living matter evolving from self-replicating but non-living molecules,<ref name="Bernal 1967" /><ref>{{harvnb|Bryson|2004|pp=300–302}}</ref> and proposed that biopoiesis passes through a number of intermediate stages.

A research project completed in 2015 by John Sutherland and others found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, as well as those of RNA, while not producing a wide range of other compounds. The researchers used the term "cyanosulfidic" to describe this network of reactions. The Miller–Urey experiment, for example, produces many substances that would react with the amino acids or terminate their coupling into peptide chains.

2015年由 John Sutherland 和其他人完成的一个研究项目发现，一个以氰化氢和硫化氢开始的反应网络，在紫外线照射的水流中，可以产生蛋白质和脂质的化学成分，以及 RNA 的化学成分，同时不产生大量其他化合物。研究人员用“氰磺酸盐”这个术语来描述这个反应网络。例如，Miller-Urey 实验产生了许多物质，这些物质会与氨基酸发生反应，或者终止它们的偶联形成肽链。

[[Robert Shapiro (chemist)|Robert Shapiro]] has summarized the "primordial soup" theory of Oparin and Haldane in its "mature form" as follows:<ref>{{harvnb|Shapiro|1987|p=110}}</ref>

# The early Earth had a chemically [[reducing atmosphere]].

# This atmosphere, exposed to [[energy]] in various forms, produced simple organic compounds ("[[monomer]]s").

Autocatalysts are substances that catalyze the production of themselves and therefore are "molecular replicators." The simplest self-replicating chemical systems are autocatalytic, and typically contain three components: a product molecule and two precursor molecules. The product molecule joins together the precursor molecules, which in turn produce more product molecules from more precursor molecules. The product molecule catalyzes the reaction by providing a complementary template that binds to the precursors, thus bringing them together. Such systems have been demonstrated both in biological macromolecules and in small organic molecules. Systems that do not proceed by template mechanisms, such as the self-reproduction of micelles and vesicles, have also been observed. British ethologist Richard Dawkins wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book The Ancestor's Tale. In his book, Dawkins cites experiments performed by Julius Rebek and his colleagues in which they combined amino adenosine and pentafluorophenyl esters with the autocatalyst amino adenosine triacid ester (AATE). One product was a variant of AATE, which catalyzed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.

自动催化剂是催化自身生成的物质，因此是“分子复制因子”最简单的自我复制化学系统是自动催化，通常包含三个组成部分: 一个产物分子和两个前体分子。产物分子将前体分子连接在一起，这些前体分子又从更多前体分子中产生更多的产物分子。产物分子通过提供一个与前体结合的互补模板来催化反应，从而使它们结合在一起。这种体系已在生物大分子和有机小分子中得到证明。不依靠模板机制进行的系统，例如胶束和囊泡的自我复制，也被观察到。英国动物行为学家理查德 · 道金斯在他2004年出版的《祖先的故事》一书中提到了自我催化作为对生命起源的潜在解释。在他的书中，道金斯引用了朱利叶斯 · 雷贝克和他的同事所做的实验，他们将氨基腺苷和五氟苯基酯与氨基腺苷三酸酯(AATE)结合在一起。其中一种产品是 AATE 的变体，它能催化自身的合成。这个实验证明了自动催化剂在具有遗传性的实体种群中表现出竞争的可能性，这可以被解释为自然选择的一种基本形式。

# These compounds accumulated in a "soup" that may have concentrated at various locations (shorelines, [[Hydrothermal vent|oceanic vents]] etc.).

# By further transformation, more complex organic [[polymer]]s—and ultimately life—developed in the soup.

===John Bernal===

John Bernal showed that based upon this and subsequent work there is no difficulty in principle in forming most of the molecules we recognize as the necessary molecules for life from their inorganic precursors. The underlying hypothesis held by Oparin, Haldane, Bernal, Miller and Urey, for instance, was that multiple conditions on the primeval Earth favoured chemical reactions that synthesized the same set of complex organic compounds from such simple precursors.

Bernal coined the term ''biopoiesis'' in 1949 to refer to the origin of life.<ref>{{harvnb|Bernal|1951}}</ref> In 1967, he suggested that it occurred in three "stages":

# the origin of biological monomers

# the origin of biological polymers

# the evolution from molecules to cells

Researchers Tony Jia and Kuhan Chandru have proposed that membraneless polyesters droplets could have been significant in the Origins of Life. Given the "messy" nature of prebiotic chemistry, the spontaneous generation of these combinatorial droplets may have played a role in early cellularization before the innovation of lipid vesicles. Protein function within and RNA function in the presence of certain polyester droplets was shown to be preserved within the droplets. Additionally, the droplets have scaffolding ability, by allowing lipids to assemble around them that may have prevented leakage of genetic materials.

研究人员 Tony Jia 和 Kuhan Chandru 提出，无膜聚酯小滴可能在生命起源中具有重要意义。鉴于生命起源前化学的“混乱”本质，这些组合液滴的自然发生可能在脂质小泡发明之前的早期纤维化过程中发挥了作用。蛋白质功能和 RNA 功能在某些聚酯液滴的存在被证明是保留在液滴。此外，液滴具有支架能力，它允许脂质聚集在液滴周围，这可能阻止了遗传物质的泄漏。

Bernal suggested that evolution commenced between stages 1 and 2. Bernal regarded the third stage, in which biological reactions were incorporated behind a cell's boundary, as the most difficult. Modern work on the way that [[cell membrane]]s self-assemble, and the work on micropores in various substrates, may be a key step towards understanding the development of independent free-living cells.<ref>{{cite journal |last= Martin |first= William F. |authorlink= William F. Martin |date= January 2003 |title= On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells |journal=Phil. Trans. R. Soc. Lond. A |volume= 358 |issue= 1429 |pages= 59–83 |doi= 10.1098/rstb.2002.1183 |pmid=12594918 |pmc=1693102}}</ref><ref>{{cite journal |last= Bernal |first= John Desmond |authorlink= John Desmond Bernal |date= September 1949 |title= The Physical Basis of Life |journal= Proceedings of the Physical Society, Section A |volume= 62 |issue= 9 |pages= 537–558 |bibcode= 1949PPSA...62..537B |doi= 10.1088/0370-1298/62/9/301 }}</ref><ref>{{harvnb|Kauffman|1995}}</ref>

Fox observed in the 1960s that the proteinoids that he had synthesized could form cell-like structures that have been named "proteinoid microspheres".

福克斯在20世纪60年代观察到，他合成的蛋白质可以形成细胞样结构，被命名为“类蛋白微球”。

===Miller–Urey experiment===

[[File:Miller1999.jpg|thumb|left|upright|Stanley Miller]]

The amino acids had combined to form proteinoids, and the proteinoids had combined to form small globules that Fox called "microspheres". His proteinoids were not cells, although they formed clumps and chains reminiscent of cyanobacteria, but they contained no functional nucleic acids or any encoded information. Based upon such experiments, Colin Pittendrigh stated in 1967 that "laboratories will be creating a living cell within ten years," a remark that reflected the typical contemporary naivety about the complexity of cell structures.

氨基酸结合形成蛋白质，蛋白质结合形成小球，福克斯称之为“微球”。他的蛋白质不是细胞，虽然它们形成的团块和链让人想起蓝藻，但是它们不包含任何功能性核酸或编码信息。基于这些实验，科林 · 皮滕德里在1967年表示，“实验室将在10年内创造出一个活细胞” ，这句话反映了当代对细胞结构复杂性的典型天真。

[[File:Miller-Urey.jpg|thumb|upright=1.5|Miller–Urey experiment JP]] One of the most important pieces of experimental support for the "soup" theory came in 1952. [[Stanley L. Miller|Stanley Miller]] and [[Harold C. Urey|Harold Urey]] performed an experiment that demonstrated how organic molecules could have spontaneously formed from inorganic precursors under conditions like those posited by the Oparin-Haldane hypothesis. The now-famous [[Miller–Urey experiment]] used a highly reducing mixture of gases—[[methane]], [[ammonia]], and [[hydrogen gas|hydrogen]], as well as [[water vapor]]—to form simple organic monomers such as amino acids.<ref>{{cite journal |last=Miller |first=Stanley L. |authorlink=Stanley Miller |date=15 May 1953 |title=A Production of Amino Acids Under Possible Primitive Earth Conditions |journal=[[Science (journal)|Science]] |volume=117 |issue=3046 |pages=528–529 |bibcode=1953Sci...117..528M |doi=10.1126/science.117.3046.528 |pmid=13056598}}</ref> The mixture of gases was cycled through an apparatus that delivered electrical sparks to the mixture. After one week, it was found that about 10% to 15% of the carbon in the system was then in the form of a [[racemic mixture]] of organic compounds, including amino acids, which are the building blocks of [[protein]]s. This provided direct experimental support for the second point of the "soup" theory, and it is around the remaining two points of the theory that much of the debate now centers.

A 2011 reanalysis of the saved vials containing the original extracts that resulted from the Miller and Urey experiments, using current and more advanced analytical equipment and technology, has uncovered more biochemicals than originally discovered in the 1950s. One of the more important findings was 23 amino acids, far more than the five originally found.<ref name="pmid21422282">{{cite journal |last1=Parker |first1=Eric T. |last2=Cleaves |first2=Henderson J. |last3=Dworkin |first3=Jason P. |last4=Glavin |first4=Daniel P. |last5=Callahan |first5=Michael |last6=Aubrey |first6=Andrew |last7=Lazcano |first7=Antonio |last8=Bada |first8=Jeffrey L. |display-authors=3 |date=5 April 2011 |title=Primordial synthesis of amines and amino acids in a 1958 Miller H2S-rich spark discharge experiment |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=108 |issue=14 |pages=5526–5531 |bibcode=2011PNAS..108.5526P |doi=10.1073/pnas.1019191108 |pmc=3078417 |pmid=21422282 }}</ref>

== Primordial origin of biological molecules: Chemistry ==

The lipid world theory postulates that the first self-replicating object was lipid-like. It is known that phospholipids form lipid bilayers in water while under agitation—the same structure as in cell membranes. These molecules were not present on early Earth, but other amphiphilic long-chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favourably. Studies on vesicles from potentially prebiotic amphiphiles have so far been limited to systems containing one or two types of amphiphiles. This in contrast to the output of simulated prebiotic chemical reactions, which typically produce very heterogeneous mixtures of compounds. actually a positive feedback composed of two mutual catalysts represented by a membrane site and a specific compound trapped in the vesicle. Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct lineages of vesicles which would have allowed Darwinian natural selection.

脂质世界理论假定，第一个自我复制的物体是类脂的。众所周知，磷脂在水中搅拌时形成类脂双分子层，其结构与细胞膜相同。这些分子在早期地球上并不存在，但其他两亲性长链分子也形成膜。此外，这些机构可能会扩大(通过插入额外的脂质) ，在过度扩张下可能会发生自发的分裂，这保留了相同的大小和组成的脂质在两个后代。这一理论的主要思想是，脂质体的分子组成是信息存储的初始方式，进化导致了 RNA 或 DNA 等高分子实体的出现，这些高分子实体可以有利地存储信息。到目前为止，对具有潜在前生命的两亲体的囊泡的研究仅限于含有一种或两种两亲体的系统。这与模拟生命前化学反应的输出形成了鲜明的对比，模拟生命前化学反应通常产生非常多样的化合物混合物。实际上是由两个相互作用的催化剂组成的正反馈，表现为一个膜位点和一个被困在囊泡中的特定化合物。这样的位点/复合对可传染给子囊泡，导致出现不同的囊泡谱系，这使得达尔文的自然选择成为可能。

The chemical processes on the pre-biotic early Earth are called [[chemical evolution (disambiguation)|''chemical evolution'']].

The [[Chemical element|elements]], except for hydrogen and helium, ultimately derive from [[stellar nucleosynthesis]]. In 2016, astronomers reported that the very basic chemical ingredients of [[life]]—the [[Carbon-hydrogen bond|carbon-hydrogen molecule]] (CH, or [[methylidyne radical]]), the carbon-hydrogen positive ion (CH+) and the carbon ion (C+)—are largely the result of [[ultraviolet light]] from stars, rather than other forms of radiation from [[supernovae]] and [[young star]]s, as thought earlier.<ref name="NASA-20161012">{{cite web |last=Landau |first=Elizabeth |title=Building Blocks of Life's Building Blocks Come From Starlight |url=http://www.jpl.nasa.gov/news/news.php?feature=6645 |date=12 October 2016 |work=[[NASA]] |accessdate=13 October 2016 |url-status=live |archiveurl=https://web.archive.org/web/20161013135018/http://www.jpl.nasa.gov/news/news.php?feature=6645 |archivedate=13 October 2016}}</ref> Complex molecules, including organic molecules, form naturally both in space and on planets.<ref name="Ehrenfreund2010" /> There are two possible sources of organic molecules on the early Earth:

# Terrestrial origins – organic molecule synthesis driven by impact shocks or by other energy sources (such as UV light, [[Organic redox reaction|redox]] coupling, or electrical discharges; e.g., Miller's experiments)

# Extraterrestrial origins – formation of organic molecules in [[Interstellar cloud|interstellar dust clouds]], which rain down on planets.<ref name="Gawlowicz 2011">{{cite news |last=Gawlowicz |first=Susan |date=6 November 2011 |title=Carbon-based organic 'carriers' in interstellar dust clouds? Newly discovered diffuse interstellar bands |url=https://www.sciencedaily.com/releases/2011/11/111102161149.htm |work=[[Science Daily]] |location=Rockville, MD |publisher=ScienceDaily, LLC |accessdate=2015-06-08 |url-status=live |archiveurl=https://web.archive.org/web/20150711114643/https://www.sciencedaily.com/releases/2011/11/111102161149.htm |archivedate=11 July 2015}} Post is reprinted from materials provided by the [[Rochester Institute of Technology]].

The three main structures [[phospholipids form spontaneously in solution: the liposome (a closed bilayer), the micelle and the bilayer.]]

三个主要结构[磷脂在溶液中自发形成: 脂质体(闭合双分子层) ，胶束和双分子层]

* {{cite journal |last1=Geballe |first1=Thomas R. |last2=Najarro |first2=Francisco |last3=Figer |first3=Donald F. |authorlink3=Donald Figer |last4=Schlegelmilch |first4=Barret W. |last5=de la Fuente |first5=Diego |display-authors=3 |date=10 November 2011 |title=Infrared diffuse interstellar bands in the Galactic Centre region |journal=Nature |volume=479 |issue=7372 |pages=200–202 |arxiv=1111.0613 |bibcode=2011Natur.479..200G |doi=10.1038/nature10527 |pmid=22048316|s2cid=17223339 }}</ref><ref>{{harvnb|Klyce|2001}}</ref> (See [[Panspermia#Pseudo-panspermia|pseudo-panspermia]])

A protocell is a self-organized, self-ordered, spherical collection of lipids proposed as a stepping-stone to the origin of life. A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation driving the evolution of life. Although a functional protocell has not yet been achieved in a laboratory setting, there are scientists who think the goal is well within reach.

原始细胞是一个自我组织，自我有序，球形脂质收集提议作为踏脚石的生命起源。进化中的一个核心问题是，简单的原始细胞是如何产生的，以及它们对下一代生命进化的生殖贡献如何不同。虽然功能性的原始细胞还没有在实验室环境中实现，但是有些科学家认为这个目标是可以实现的。

=== Observed extraterrestrial organic molecules ===

Self-assembled vesicles are essential components of primitive cells. Researchers Irene Chen and Szostak amongst others, suggest that simple physicochemical properties of elementary protocells can give rise to essential cellular behaviours, including primitive forms of differential reproduction competition and energy storage. Such cooperative interactions between the membrane and its encapsulated contents could greatly simplify the transition from simple replicating molecules to true cells. The main advantages of encapsulation include the increased solubility of the contained cargo within the capsule and the storage of energy in the form of an electrochemical gradient.

自组装囊泡是原始细胞的重要组成部分。研究人员 Irene Chen 和 Szostak 等人提出，基本原始细胞的简单物理化学性质可以引起基本的细胞行为，包括原始形式的差异生殖竞争和能量储存。这种膜与包膜内容物之间的协同作用可以极大地简化从简单复制分子到真正细胞的过渡。包封的主要优点包括增加了胶囊内所含货物的溶解度和以电化梯度的形式储存能量。

{{See also|List of interstellar and circumstellar molecules|Panspermia#Pseudo-panspermia}}

An organic compound is any member of a large class of gaseous, liquid, or solid chemicals whose molecules contain carbon. Carbon is the [[Abundance of the chemical elements|fourth most abundant element in the Universe by mass]] after hydrogen, [[helium]], and oxygen.<ref>{{cite encyclopedia |encyclopedia=Encyclopedia of Science |title=biological abundance of elements |url=http://www.daviddarling.info/encyclopedia/E/elbio.html |publisher=David Darling Enterprises |location=Dundee, Scotland |accessdate=2008-10-09 |url-status=live |archiveurl=https://web.archive.org/web/20120204033420/http://www.daviddarling.info/encyclopedia/E/elbio.html |archivedate=4 February 2012}}</ref> Carbon is abundant in the Sun, stars, comets, and in the [[Celestial body's atmosphere|atmospheres]] of most planets.<ref name="NASA-20140221">{{cite web |url=http://www.nasa.gov/ames/need-to-track-organic-nano-particles-across-the-universe-nasas-got-an-app-for-that/ |title=Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That |last=Hoover |first=Rachel |date=21 February 2014 |website=[[Ames Research Center]] |publisher=NASA |location=Mountain View, CA |accessdate=2015-06-22 |url-status=live |archiveurl=https://web.archive.org/web/20150906061428/http://www.nasa.gov/ames/need-to-track-organic-nano-particles-across-the-universe-nasas-got-an-app-for-that/ |archivedate=6 September 2015}}</ref> Organic compounds are relatively common in space, formed by "factories of complex molecular synthesis" which occur in [[molecular cloud]]s and [[circumstellar envelope]]s, and chemically evolve after reactions are initiated mostly by [[ionizing radiation]].<ref name="Ehrenfreund2010">{{cite journal |last1=Ehrenfreund |first1=Pascale |last2=Cami |first2=Jan |date=December 2010 |title=Cosmic carbon chemistry: from the interstellar medium to the early Earth. |journal=Cold Spring Harbor Perspectives in Biology |volume=2 |issue=12 |page=a002097 |doi=10.1101/cshperspect.a002097 |pmc=2982172 |pmid=20554702}}</ref><ref name="FromADistantComet">{{cite news |last=Chang |first=Kenneth |date=18 August 2009 |title=From a Distant Comet, a Clue to Life |url=https://www.nytimes.com/2009/08/19/science/space/19comet.html |newspaper=The New York Times |location=New York |page=A18 |accessdate=2015-06-22 |url-status=live |archiveurl=https://web.archive.org/web/20150623005046/http://www.nytimes.com/2009/08/19/science/space/19comet.html |archivedate=23 June 2015}}</ref><ref>{{cite journal |last1=Goncharuk |first1=Vladislav V. |last2=Zui |first2=O. V. |date=February 2015 |title=Water and carbon dioxide as the main precursors of organic matter on Earth and in space |journal=Journal of Water Chemistry and Technology |volume=37 |issue=1 |pages=2–3 |doi=10.3103/S1063455X15010026 |s2cid=97965067 }}</ref><ref>{{cite journal |last1=Abou Mrad |first1=Ninette |last2=Vinogradoff |first2=Vassilissa |last3=Duvernay |first3=Fabrice |last4=Danger |first4=Grégoire |last5=Theulé |first5=Patrice |last6=Borget |first6=Fabien |last7=Chiavassa |first7=Thierry |display-authors=3 |year=2015 |title=Laboratory experimental simulations: Chemical evolution of the organic matter from interstellar and cometary ice analogs |url=http://popups.ulg.ac.be/0037-9565/index.php?id=4621&file=1|journal=Bulletin de la Société Royale des Sciences de Liège |volume=84 |pages=21–32 |bibcode=2015BSRSL..84...21A |accessdate=2015-04-06 |url-status=live |archiveurl=https://web.archive.org/web/20150413050621/http://popups.ulg.ac.be/0037-9565/index.php?id=4621&file=1 |archivedate=13 April 2015}}</ref> Based on [[computer simulation|computer model studies]], the complex organic molecules necessary for life may have formed on dust grains in the protoplanetary disk surrounding the Sun before the formation of the Earth.<ref name="Space-20120329" /> According to the computer studies, this same process may also occur around other stars that acquire planets.<ref name="Space-20120329" />

A 2012 study led by Mulkidjanian of the University of Osnabrück, suggests that inland pools of condensed and cooled geothermal vapor have the ideal characteristics for the origin of life. Scientists confirmed in 2002 that by adding a montmorillonite clay to a solution of fatty acid micelles (lipid spheres), the clay sped up the rate of vesicles formation 100-fold.

奥斯纳布吕克大学的 Mulkidjanian 在2012年领导的一项研究表明，内陆凝结冷却的地热蒸汽池具有生命起源的理想特征。科学家在2002年证实，通过在脂肪酸胶束(脂球)的溶液中加入蒙脱石粘土，这种粘土加快了囊泡形成的速度100倍。

====Amino acids====

NASA announced in 2009 that scientists had identified another fundamental chemical building block of life in a comet for the first time, glycine, an amino acid, which was detected in material ejected from comet [[81P/Wild|Wild 2]] in 2004 and grabbed by NASA's [[Stardust (spacecraft)|''Stardust'']] probe. Glycine has been detected in meteorites before. Carl Pilcher, who leads the [[NASA Astrobiology Institute]] commented that <blockquote>The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the universe may be common rather than rare.<ref>{{cite news |author= |date=18 August 2009 |title='Life chemical' detected in comet |url=http://news.bbc.co.uk/2/hi/science/nature/8208307.stm |work=BBC News |location=London |accessdate=2015-06-23 |url-status=live |archiveurl=https://web.archive.org/web/20150525071228/http://news.bbc.co.uk/2/hi/science/nature/8208307.stm |archivedate=25 May 2015}}</ref></blockquote> Comets are encrusted with outer layers of dark material, thought to be a [[tar]]-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by ionizing radiation. It is possible that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth.<ref>{{cite journal |last1=Thompson |first1=William Reid |last2=Murray |first2=B. G. |last3=Khare |first3=Bishun Narain |authorlink3=Bishun Khare |last4=Sagan |first4=Carl |date=30 December 1987 |title=Coloration and darkening of methane clathrate and other ices by charged particle irradiation: Applications to the outer solar system |journal=[[Journal of Geophysical Research]] |volume=92 |issue=A13 |pages=14933–14947 |bibcode=1987JGR....9214933T |doi=10.1029/JA092iA13p14933 |pmid=11542127}}</ref><ref>{{cite web |url=https://www.llnl.gov/news/life-earth-shockingly-comes-out-world |title=Life on Earth shockingly comes from out of this world |last=Stark |first=Anne M. |date=5 June 2013 |publisher=[[Lawrence Livermore National Laboratory]] |location=Livermore, CA |accessdate=2015-06-23 |url-status=live |archiveurl=https://web.archive.org/web/20150916135630/https://www.llnl.gov/news/life-earth-shockingly-comes-out-world |archivedate=16 September 2015}}</ref><ref>{{cite journal |last1=Goldman |first1=Nir |last2=Tamblyn |first2=Isaac |date=20 June 2013 |title=Prebiotic Chemistry within a Simple Impacting Icy Mixture |journal=[[Journal of Physical Chemistry A]] |volume=117 |issue=24 |pages=5124–5131 |doi=10.1021/jp402976n |pmid=23639050|bibcode=2013JPCA..117.5124G |url=http://nparc.nrc-cnrc.gc.ca/eng/view/fulltext/?id=e89d2ac7-4cf8-40e0-bcc9-3c53f68ed70a }}</ref> Amino acids which were formed extraterrestrially may also have arrived on Earth via comets.<ref name="Follmann2009" /> It is estimated that during the Late Heavy Bombardment, meteorites may have delivered up to five million [[ton]]s of organic prebiotic elements to Earth per year.<ref name="Follmann2009" />

Bruce Damer and David Deamer have come to the conclusion that cell membranes cannot be formed in salty seawater, and must therefore have originated in freshwater. Before the continents formed, the only dry land on Earth would be volcanic islands, where rainwater would form ponds where lipids could form the first stages towards cell membranes. These predecessors of true cells are assumed to have behaved more like a superorganism rather than individual structures, where the porous membranes would house molecules which would leak out and enter other protocells. Only when true cells had evolved would they gradually adapt to saltier environments and enter the ocean.

布鲁斯 · 达默和戴维 · 迪默得出结论，细胞膜不能在含盐的海水中形成，因此一定起源于淡水。在大陆形成之前，地球上唯一的干燥陆地将是火山岛，在那里雨水将形成池塘，脂类可以形成朝向细胞膜的第一阶段。这些真正细胞的前身被认为更像是一个超个体，而不是单个的结构，在这些多孔的膜中容纳的分子会泄漏出来并进入其他的原始细胞。只有当真正的细胞进化出来后，它们才能逐渐适应更咸的环境并进入海洋。

==== PAH world hypothesis ====

{{Main|PAH world hypothesis}}

Another protocell model is the Jeewanu. First synthesized in 1963 from simple minerals and basic organics while exposed to sunlight, it is still reported to have some metabolic capabilities, the presence of semipermeable membrane, amino acids, phospholipids, carbohydrates and RNA-like molecules. However, the nature and properties of the Jeewanu remains to be clarified.

另一个原细胞模型是 Jeewanu。1963年首次在阳光下由简单矿物质和基本有机物合成，据报道它仍然具有一些新陈代谢能力，包括半透膜、氨基酸、磷脂、碳水化合物和类 rna 分子。然而，Jeewanu 的性质和属性仍有待澄清。

[[Polycyclic aromatic hydrocarbon]]s (PAH) are the most common and abundant of the known polyatomic molecules in the [[observable universe]], and are considered a likely constituent of the [[primordial sea]].<ref name="SP-20051018" /><ref name="AJ-20051010" /><ref name="NASA-20110413" /> In 2010, PAHs, have been detected in [[nebula]]e.<ref name="AJL-20101120">{{cite journal |last1=García-Hernández |first1=Domingo. A. |last2=Manchado |first2=Arturo |last3=García-Lario |first3=Pedro |last4=Stanghellini |first4=Letizia |last5=Villaver |first5=Eva |last6=Shaw |first6=Richard A. |last7=Szczerba |first7=Ryszard |last8=Perea-Calderón |first8=Jose Vicente |display-authors=3 |date=20 November 2010 |title=Formation of Fullerenes in H-Containing Planetary Nebulae |journal=The Astrophysical Journal Letters |volume=724 |issue=1 |pages=L39–L43 |arxiv=1009.4357 |bibcode=2010ApJ...724L..39G |doi=10.1088/2041-8205/724/1/L39 |s2cid=119121764 }}</ref>



[[File:PIA22568-CatsPawNebula-Spitzer-20181023.jpg|thumb|upright=1.3|The [[Cat's Paw Nebula]] lies inside the [[Milky Way Galaxy]] and is located in the [[constellation]] [[Scorpius]]. Green areas show regions where radiation from hot stars collided with large molecules and small dust grains called "[[polycyclic aromatic hydrocarbon]]s" (PAHs), causing them to [[fluoresce]]. ([[Spitzer space telescope]], 2018)]]

Polycyclic aromatic hydrocarbons (PAH) are known to be abundant in the universe,<ref name="SP-20051018">{{cite news |last= Carey |first= Bjorn |date= 18 October 2005 |title= Life's Building Blocks 'Abundant in Space' |url= http://www.space.com/1686-life-building-blocks-abundant-space.html |website= Space.com |location= Watsonville, CA |publisher= [[Imaginova]] |accessdate= 2015-06-23 |url-status= live |archiveurl= https://web.archive.org/web/20150626223942/http://www.space.com/1686-life-building-blocks-abundant-space.html |archivedate= 26 June 2015}}</ref><ref name="AJ-20051010">{{cite journal |last1=Hudgins |first1= Douglas M. |last2=Bauschlicher |first2=Charles W. Jr. |last3=Allamandola |first3=Louis J. |date=10 October 2005 |title=Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population |journal=[[The Astrophysical Journal]] |volume=632 |pages=316–332 |issue=1 |bibcode=2005ApJ...632..316H |doi=10.1086/432495 |citeseerx=10.1.1.218.8786 }}</ref><ref name="NASA-20110413">{{cite web|url=http://amesteam.arc.nasa.gov/Research/cosmic.html |title=Cosmic Distribution of Chemical Complexity |last1=Des Marais |first1=David J. |last2=Allamandola |first2=Louis J. |last3=Sandford |first3=Scott |authorlink3=Scott Sandford |last4=Mattioda |first4=Andrew |last5=Gudipati |first5=Murthy |last6=Roser |first6=Joseph |last7=Bramall |first7=Nathan |last8=Nuevo |first8=Michel |last9=Boersma |first9=Christiaan |last10=Bernstein |first10=Max |last11=Peeters |first11=Els |last12=Cami |first12=Jan |last13=Cook |first13=Jamie Elsila |last14=Dworkin |first14=Jason |display-authors=3 |year=2009 |website=Ames Research Center |publisher=NASA |location=Mountain View, CA |accessdate=2015-06-24 |url-status=dead |archiveurl=https://web.archive.org/web/20140227184503/http://amesteam.arc.nasa.gov/Research/cosmic.html |archivedate=27 February 2014}} See the Ames Research Center 2009 annual team report to the [[NASA Astrobiology Institute]] here {{cite web|url=https://astrobiology.nasa.gov/nai/reports/annual-reports/2009/arc/ |title=Archived copy |accessdate=2015-06-24 |url-status=dead |archiveurl=https://web.archive.org/web/20130301064911/https://astrobiology.nasa.gov/nai/reports/annual-reports/2009/arc/ |archivedate=1 March 2013}}.</ref> including in the [[interstellar medium]], in comets, and in meteorites, and are some of the most complex molecules so far found in space.<ref name="NASA-20140221" />

An early concept, that life originated from non-living matter in slow stages, appeared in Herbert Spencer's 1864–1867 book Principles of Biology. In 1879 William Turner Thiselton-Dyer referred to this in a paper "On spontaneous generation and evolution". On 1 February 1871 Charles Darwin wrote about these publications to Joseph Hooker, and set out his own speculation, suggesting that the original spark of life may have begun in a <blockquote>warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, , present, that a compound was chemically formed ready to undergo still more complex changes.</blockquote> He went on to explain that <blockquote>at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.</blockquote>

在赫伯特 · 斯宾塞1864-1867年出版的《生物学原理》一书中，有一个早期的概念，认为生命起源于非生命物质的缓慢阶段。1879年，威廉·特纳·西塞尔顿-戴尔在一篇名为《论自然发生与进化论》的论文中提到了这一点。1871年2月1日，查尔斯 · 达尔文写信给约瑟夫 · 胡克，提出了他自己的猜测，认为生命的原始火花可能是从一个温暖的小池塘开始的，里面有各种各样的氨和磷酸盐，光，热，电，现在，一种化合物已经被化学形成，可以进行更复杂的变化。他接着解释说，在今天，这种物质会立即被吞噬或吸收，而在生物形成之前是不会发生这种情况的。</blockquote >

Other sources of complex molecules have been postulated, including extraterrestrial stellar or interstellar origin. For example, from spectral analyses, organic molecules are known to be present in comets and meteorites. In 2004, a team detected traces of PAHs in a nebula.<ref>{{cite conference |last1=Witt |first1=Adolf N. |last2=Vijh |first2=Uma P. |last3=Gordon |first3=Karl D. |date=January 2004 |title=Discovery of Blue Fluorescence by Polycyclic Aromatic Hydrocarbon Molecules in the Red Rectangle |url=https://aas.org/archives/BAAS/v35n5/aas203/189.htm |publisher=[[American Astronomical Society]] |bibcode=2003AAS...20311017W |archiveurl=https://web.archive.org/web/20031219175322/http://www.aas.org/publications/baas/v35n5/aas203/189.htm |archivedate=19 December 2003 |url-status=dead |conference=American Astronomical Society Meeting 203 |location=Atlanta, GA |access-date=16 January 2019 }}</ref> In 2010, another team also detected PAHs, along with fullerenes, in nebulae.<ref name="AJL-20101120" /> The use of PAHs has also been proposed as a precursor to the RNA world in the PAH world hypothesis.<ref>{{Cite journal|last1=d'Ischia|first1=Marco|last2=Manini|first2=Paola|last3=Moracci|first3=Marco|last4=Saladino|first4=Raffaele|last5=Ball|first5=Vincent|last6=Thissen|first6=Helmut|last7=Evans|first7=Richard A.|last8=Puzzarini|first8=Cristina|last9=Barone|first9=Vincenzo|date=2019-08-21|title=Astrochemistry and Astrobiology: Materials Science in Wonderland?|journal=International Journal of Molecular Sciences|volume=20|issue=17|pages=4079|doi=10.3390/ijms20174079|issn=1422-0067|pmc=6747172|pmid=31438518}}</ref> The [[Spitzer Space Telescope]] has detected a star, HH 46-IR, which is forming by a process similar to that by which the Sun formed. In the disk of material surrounding the star, there is a very large range of molecules, including cyanide compounds, [[hydrocarbon]]s, and carbon monoxide. In 2012, NASA scientists reported that PAHs, subjected to interstellar medium conditions, are transformed, through [[hydrogenation]], [[Oxygenate|oxygenation]] and [[hydroxylation]], to more complex organics—"a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively."<ref name="Space-20120920">{{cite web |url= http://www.space.com/17681-life-building-blocks-nasa-organic-molecules.html |title= NASA Cooks Up Icy Organics to Mimic Life's Origins |date= 20 September 2012 |website= Space.com |location= Ogden, UT |publisher= Purch |accessdate= 2015-06-26 |url-status= live |archiveurl= https://web.archive.org/web/20150625035023/http://www.space.com/17681-life-building-blocks-nasa-organic-molecules.html |archivedate= 25 June 2015}}</ref><ref name="AJL-20120901">{{cite journal |last1=Gudipati |first1=Murthy S. |author2=Rui Yang |date=1 September 2012 |title=In-situ Probing of Radiation-induced Processing of Organics in Astrophysical Ice Analogs – Novel Laser Desorption Laser Ionization Time-of-flight Mass Spectroscopic Studies |journal=The Astrophysical Journal Letters |volume=756 |issue=1 |bibcode=2012ApJ...756L..24G |doi=10.1088/2041-8205/756/1/L24 |pages=L24}}</ref> Further, as a result of these transformations, the PAHs lose their [[Spectroscopy|spectroscopic signature]] which could be one of the reasons "for the lack of PAH detection in [[interstellar ice]] grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks."<ref name="Space-20120920" /><ref name="AJL-20120901" />

:

:

NASA maintains a database for tracking PAHs in the universe.<ref name="NASA-20140221" /><ref>{{cite web |url=http://www.astrochem.org/pahdb/ |title=NASA Ames PAH IR Spectroscopic Database |publisher=NASA |accessdate=2015-06-17 |url-status=live |archiveurl=https://web.archive.org/web/20150629185734/http://www.astrochem.org/pahdb/ |archivedate=29 June 2015}}</ref> More than 20% of the carbon in the universe may be associated with PAHs,<ref name="NASA-20140221" /><ref name="NASA-20140221" /> possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe,<ref name="SP-20051018" /><ref name="AJ-20051010" /><ref name="NASA-20110413" /> and are associated with [[Star formation|new stars]] and [[exoplanet]]s.<ref name="NASA-20140221" />

It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, , present, that a compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.

人们常说，第一次产生生命有机体的所有条件现在都具备了，而这些条件本来是可以具备的。但是如果(哦！多大的如果啊!)我们可以设想在一个温暖的小池塘里，有各种各样的氨和磷酸盐，光，热，电，现在，一种化合物已经形成，可以进行更复杂的变化，现在这种物质会立即被吞噬或吸收，这在生物形成之前是不可能的。

====Nucleobases====

— Darwin, 1 February 1871

ー达尔文，1871年2月1日

Observations suggest that the majority of organic compounds introduced on Earth by interstellar dust particles are considered principal agents in the formation of complex molecules, thanks to their peculiar [[catalysis|surface-catalytic]] activities.<ref name="Lincei">{{cite journal |last=Gallori |first=Enzo |title=Astrochemistry and the origin of genetic material |journal=Rendiconti Lincei |date=June 2011 |volume=22 |issue=2 |pages=113–118 |doi=10.1007/s12210-011-0118-4 |s2cid=96659714 }} "Paper presented at the Symposium 'Astrochemistry: molecules in space and time' (Rome, 4–5 November 2010), sponsored by Fondazione 'Guido Donegani', Accademia Nazionale dei Lincei."</ref><ref>{{cite journal |last=Martins |first=Zita |authorlink=Zita Martins |date=February 2011 |title=Organic Chemistry of Carbonaceous Meteorites |journal=[[Elements (journal)|Elements]] |volume=7 |issue=1 |pages=35–40 |doi=10.2113/gselements.7.1.35 }}</ref> Studies reported in 2008, based on 12C/13C [[Natural abundance|isotopic ratios]] of organic compounds found in the Murchison meteorite, suggested that the RNA component uracil and related molecules, including [[xanthine]], were formed extraterrestrially.<ref name="Murch_base">{{cite journal |last1=Martins |first1=Zita |last2=Botta |first2=Oliver |last3=Fogel |first3=Marilyn L. |last4=Sephton |first4=Mark A. |last5=Glavin |first5=Daniel P. |last6=Watson |first6=Jonathan S. |last7=Dworkin |first7=Jason P. |last8=Schwartz |first8=Alan W. |last9=Ehrenfreund |first9=Pascale |display-authors=3 |date=15 June 2008 |title=Extraterrestrial nucleobases in the Murchison meteorite |journal=Earth and Planetary Science Letters |volume=270 |issue=1–2 |pages=130–136 |bibcode=2008E&PSL.270..130M |arxiv=0806.2286 |doi=10.1016/j.epsl.2008.03.026 |s2cid=14309508 }}</ref><ref>{{cite news |author= |date=14 June 2008 |title=We may all be space aliens: study |url=http://www.abc.net.au/news/2008-06-14/we-may-all-be-space-aliens-study/2471434 |location=Sydney |publisher=[[Australian Broadcasting Corporation]] |agency=[[Agence France-Presse]] |accessdate=2015-06-22 |url-status=live |archiveurl=https://web.archive.org/web/20150623073332/http://www.abc.net.au/news/2008-06-14/we-may-all-be-space-aliens-study/2471434 |archivedate=23 June 2015}}</ref> In 2011, a report based on [[NASA]] studies of meteorites found on Earth was published suggesting DNA components (adenine, guanine and related organic molecules) were made in outer space.<ref name="Lincei" /><ref name="Callahan">{{cite journal |last1=Callahan |first1=Michael P. |last2=Smith |first2=Karen E. |last3=Cleaves |first3=H. James, II |last4=Ruzica |first4=Josef |last5=Stern |first5=Jennifer C. |last6=Glavin |first6=Daniel P. |last7=House |first7=Christopher H. |last8=Dworkin |first8=Jason P. |display-authors=3 |date=23 August 2011 |title=Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=108 |issue=34 |pages=13995–13998 |bibcode=2011PNAS..10813995C |doi=10.1073/pnas.1106493108 |pmc=3161613 |pmid=21836052}}</ref><ref name="Steigerwald">{{cite web |url=http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |title=NASA Researchers: DNA Building Blocks Can Be Made in Space |last=Steigerwald |first=John |date=8 August 2011 |work=[[Goddard Space Flight Center]] |publisher=NASA |location=Greenbelt, MD |accessdate=2015-06-23 |url-status=live |archiveurl=https://web.archive.org/web/20150623004556/http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |archivedate=23 June 2015}}</ref> Scientists also found that the [[cosmic dust]] permeating the universe contains complex organics ("amorphous organic solids with a mixed [[Aromaticity|aromatic]]–[[Aliphatic compound|aliphatic]] structure") that could be created naturally, and rapidly, by stars.<ref name="Space-20111026">{{cite news |last= Chow |first= Denise |date= 26 October 2011 |title= Discovery: Cosmic Dust Contains Organic Matter from Stars |url= http://www.space.com/13401-cosmic-star-dust-complex-organic-compounds.html |website= Space.com |location= Ogden, UT |publisher= Purch |accessdate= 2015-06-23 |url-status= live |archiveurl= https://web.archive.org/web/20150714084901/http://www.space.com/13401-cosmic-star-dust-complex-organic-compounds.html |archivedate= 14 July 2015}}</ref><ref name="ScienceDaily-20111026">{{cite news |author=The University of Hong Kong |date=27 October 2011 |title=Astronomers discover complex organic matter exists throughout the universe |url=https://www.sciencedaily.com/releases/2011/10/111026143721.htm |location=Rockville, MD |publisher= ScienceDaily, LLC |url-status=live |archiveurl=https://web.archive.org/web/20150703185252/https://www.sciencedaily.com/releases/2011/10/111026143721.htm |archivedate=3 July 2015|author-link=University of Hong Kong }}</ref><ref name="Nature-20111026">{{cite journal |author1=Sun Kwok |authorlink1=Sun Kwok |author2=Yong Zhang |date=3 November 2011 |title=Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features |journal=Nature |volume=479 |issue=7371 |pages=80–83 |bibcode=2011Natur.479...80K |doi=10.1038/nature10542 |pmid=22031328|s2cid=4419859 }}</ref> [[Sun Kwok]] of [[University of Hong Kong|The University of Hong Kong]] suggested that these compounds may have been related to the development of life on Earth said that "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."<ref name="Space-20111026" />

More recent studies, in 2017, support the notion that life may have begun right after the Earth was formed as RNA molecules emerging from "warm little ponds".

2017年的更多最新研究支持了这样的观点，即生命可能是在地球形成之后立即开始的，那时地球是从“温暖的小池塘”中冒出来的 RNA 分子。

====The sugar glycolaldehyde====

[[File:Formation of Glycolaldehyde in star dust.png|thumb|Formation of [[glycolaldehyde]] in [[Cosmic dust|stardust]]]]

Glycolaldehyde, the first example of an interstellar sugar molecule, was detected in the star-forming region near the centre of our galaxy. It was discovered in 2000 by Jes Jørgensen and Jan Hollis.<ref name=Hollis>{{cite web |url=http://www.nasa.gov/vision/universe/starsgalaxies/interstellar_sugar.html |title=Space Sugar's a Sweet Find |first1=Lara |last1=Clemence |last2=Cohen |first2=Jarrett |date=7 February 2005 |work=Goddard Space Flight Center |publisher=NASA |location=Greenbelt, MD |accessdate=2015-06-23 |url-status=live |archiveurl=https://web.archive.org/web/20160305002758/http://www.nasa.gov/vision/universe/starsgalaxies/interstellar_sugar.html |archivedate=5 March 2016}}</ref> In 2012, Jørgensen's team reported the detection of glycolaldehyde in a distant star system. The molecule was found around the [[protostar|protostellar]] binary [[IRAS 16293-2422]] 400 [[Light-year|light years]] from Earth.<ref name="NG-20120829">{{cite news |last=Than |first=Ker |date=30 August 2012 |title=Sugar Found in Space: A Sign of Life? |url=http://news.nationalgeographic.com/news/2012/08/120829-sugar-space-planets-science-life/ |work=National Geographic News |location=Washington, D.C. |publisher=[[National Geographic Society]] |accessdate=2015-06-23 |url-status=live |archiveurl=https://web.archive.org/web/20150714073830/http://news.nationalgeographic.com/news/2012/08/120829-sugar-space-planets-science-life/ |archivedate=14 July 2015}}</ref><ref name="AP-20120829">{{cite news |author= |date=29 August 2012 |title=Sweet! Astronomers spot sugar molecule near star |url=http://apnews.excite.com/article/20120829/DA0V31D80.html |work=[[Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |accessdate=2015-06-23 |url-status=live |archiveurl=https://web.archive.org/web/20150714101929/http://apnews.excite.com/article/20120829/DA0V31D80.html |archivedate=14 July 2015}}</ref><ref>{{cite web |url=http://www.news.leiden.edu/news-2012/building-blocks-for-life-found-on-young-star.html |title=Building blocks of life found around young star |author= |date=30 September 2012 |website=News & Events |publisher=[[Leiden University]] |location=Leiden, the Netherlands |accessdate=2013-12-11 |url-status=live |archiveurl=https://web.archive.org/web/20131213135815/http://www.news.leiden.edu/news-2012/building-blocks-for-life-found-on-young-star.html |archivedate=13 December 2013}}</ref> Glycolaldehyde is needed to form RNA, which is similar in function to DNA. These findings suggest that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.<ref>{{cite journal |last1=Jørgensen |first1=Jes K. |last2=Favre |first2=Cécile |last3=Bisschop |first3=Suzanne E. |last4=Bourke |first4=Tyler L. |last5=van Dishoeck |first5=Ewine F. |authorlink5=Ewine van Dishoeck |last6=Schmalzl |first6=Markus |display-authors=3 |date=2012 |title=Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA |url=http://www.eso.org/public/archives/releases/sciencepapers/eso1234/eso1234a.pdf |journal=The Astrophysical Journal Letters |volume=757 |issue=1 |arxiv=1208.5498 |bibcode=2012ApJ...757L...4J |doi=10.1088/2041-8205/757/1/L4 |accessdate=2015-06-23 |pages=L4 |s2cid=14205612 |url-status=live |archiveurl=https://web.archive.org/web/20150924021240/http://www.eso.org/public/archives/releases/sciencepapers/eso1234/eso1234a.pdf |archivedate=24 September 2015}}</ref><ref name="PNAS-20191113">{{Cite journal|last1=Furukawa|first1=Yoshihiro|last2=Chikaraishi|first2=Yoshito|last3=Ohkouchi|first3=Naohiko|last4=Ogawa|first4=Nanako O.|last5=Glavin|first5=Daniel P.|last6=Dworkin|first6=Jason P.|last7=Abe|first7=Chiaki|last8=Nakamura|first8=Tomoki|date=2019-11-13|title=Extraterrestrial ribose and other sugars in primitive meteorites|journal=Proceedings of the National Academy of Sciences|volume=116|issue=49|pages=24440–24445|language=en|doi=10.1073/pnas.1907169116|issn=0027-8424|pmid=31740594|pmc=6900709|bibcode=2019PNAS..11624440F}}</ref> Because sugars are associated with both metabolism and the [[genetic code]], two of the most basic aspects of life, it is thought the discovery of extraterrestrial sugar increases the likelihood that life may exist elsewhere in our galaxy.<ref name="Hollis" />

Martin Brazier has shown that early micro-fossils came from a hot world of gases such as methane, ammonia, carbon dioxide and hydrogen sulphide, which are toxic to much current life. Another analysis of the conventional threefold tree of life shows thermophilic and hyperthermophilic bacteria and archaea are closest to the root, suggesting that life may have evolved in a hot environment.

马丁 · 布拉泽已经证明早期的微生物化石来自于甲烷、氨、二氧化碳和硫化氢等对现代生命有毒的炽热气体。另一个对传统三重生命树的分析表明，嗜热和超嗜热细菌和古菌最接近根部，这表明生命可能是在炎热的环境中进化的。

==== Polyphosphates ====

A problem in most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of [[polyphosphate]]s.<ref>{{cite journal |last1=Brown |first1=Michael R. W. |last2=Kornberg |first2=Arthur |authorlink2=Arthur Kornberg |date=16 November 2004 |title=Inorganic polyphosphate in the origin and survival of species |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=101 |issue=46 |pages=16085–16087 |bibcode=2004PNAS..10116085B |doi=10.1073/pnas.0406909101|pmc=528972 |pmid=15520374}}</ref><ref>{{cite web |url=http://www.science.siu.edu/microbiology/micr425/425Notes/14-OriginLife.html |title=The Origin of Life |last=Clark |first=David P. |date=3 August 1999 |website=Microbiology 425: Biochemistry and Physiology of Microorganism |publisher=College of Science; [[Southern Illinois University Carbondale]] |location=Carbondale, IL |type=Lecture |archiveurl=https://web.archive.org/web/20001002142750/http://www.science.siu.edu/microbiology/micr425/425Notes/14-OriginLife.html |archivedate=2000-10-02 |url-status=dead |accessdate=2015-06-26}}</ref> Polyphosphates are formed by polymerization of ordinary monophosphate ions PO43-. Several mechanisms of organic molecule synthesis have been investigated. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as [[adenosine triphosphate]] (ATP). A key issue seems to be that calcium reacts with soluble phosphate to form insoluble [[calcium phosphate]] ([[apatite]]), so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth.<ref>{{cite journal |last=Pasek |first=Matthew A. |date=22 January 2008 |title=Rethinking early Earth phosphorus geochemistry |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=105 |issue=3 |pages=853–858 |bibcode=2008PNAS..105..853P |doi=10.1073/pnas.0708205105 |pmc=2242691 |pmid=18195373}}</ref>

Based on recent [[computer simulation|computer model studies]], the [[organic compound|complex organic molecules]] necessary for life may have formed in the [[protoplanetary disk]] of [[cosmic dust|dust grains]] surrounding the [[Sun]] before the formation of the Earth.<ref name="Space-20120329">{{cite news |last=Moskowitz |first=Clara |date=29 March 2012 |title=Life's Building Blocks May Have Formed in Dust Around Young Sun |url=http://www.space.com/15089-life-building-blocks-young-sun-dust.html |website=[[Space.com]] |location=Salt Lake City, UT |publisher=[[Purch]] |accessdate=2012-03-30 |url-status=live |archiveurl=https://web.archive.org/web/20120814205056/http://www.space.com/15089-life-building-blocks-young-sun-dust.html |archivedate=14 August 2012}}</ref><ref>{{cite journal|last1=Ciesla|first1=F.J.|last2=Sandford|first2=S.A.|title=Organic Synthesis via Irradiation and Warming of Ice Grains in the Solar Nebula|journal=Science|date=29 March 2012|volume=336|issue=6080|pages=452–454|doi=10.1126/science.1217291|pmid=22461502|bibcode=2012Sci...336..452C|hdl=2060/20120011864|s2cid=25454671|hdl-access=free}}</ref> According to the computer studies, this same process may also occur around other [[star]]s that acquire [[planet]]s. (Also see [[#Extraterrestrial organic molecules|Extraterrestrial organic molecules]]).

Deep-sea hydrothermal vent or [[black smoker]]

深海深海热泉或[[黑烟]

The deep sea vent, or alkaline hydrothermal vent, theory posits that life may have begun at submarine hydrothermal vents, Martin and Russell have suggested <blockquote>that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments,... This case is similar to the origin of life in hydrothermal vents, but with bicarbonate and calcium ions in hot water. This water has a pH of 9–11 and is possible to have the reactions in seawater. According to Melvin Calvin, certain reactions of condensation-dehydration of amino acids and nucleotides in individual blocks of peptides and nucleic acids can take place in the primary hydrosphere with pH 9–11 at a later evolutionary stage. Some of these compounds like hydrocyanic acid (HCN) have been proven in the experiments of Miller. This is the environment in which the stromatolites have been created. David Ward of Montana State University described the formation of stromatolites in hot mineral water at the Yellowstone National Park. Stromatolites survive in hot mineral water and in proximity to areas with volcanic activity. Processes have evolved in the sea near geysers of hot mineral water.

深海火山口，或者碱性深海热泉，理论断定生命可能起源于海底热液喷口，Martin 和 Russell 提出生命演化于结构化的铁单硫化物沉淀物，这些沉淀物位于哈迪安洋底的一个渗流区热液堆中，在氧化还原、 pH 值和富硫化物的热液流体与含铁的水体之间的温度梯度中。化石渗漏位点金属硫化物沉淀物中自然形成的三维区域化表明，这些无机区域是自由生活的原核生物细胞壁和细胞膜的前体。FeS 和 NiS 催化热液成分一氧化碳和甲基硫化物合成乙酰甲基硫化物的已知能力表明，这些金属硫化物壁室的内表面发生了生命前合成反应。这种情况类似于热液喷口中生命的起源，但热水中含有重碳酸盐和钙离子。这种水的 pH 值为9-11，可能在海水中发生反应。根据加尔文的研究，氨基酸和核苷酸在单个肽和核酸块中的某些缩合脱水反应可能发生在初级水圈中，pH 值为9-11，在进化的后期阶段。这些化合物中的一些，如氰化氢(HCN)已经在 Miller 的实验中被证实。这就是叠层石形成的环境。蒙大拿州立大学的 David Ward 描述了在黄石国家公园的热矿泉水中叠层石的形成。叠层石生存在热的矿泉水中，靠近火山活动的地区。在热矿泉水间歇泉附近的海洋中演化出各种过程。

The accumulation and concentration of organic molecules on a planetary surface is also considered an essential early step for the origin of life.<ref name="NASA strategy 2015"/> Identifying and understanding the mechanisms that led to the production of prebiotic

In 2011, Tadashi Sugawara from the University of Tokyo created a protocell in hot water.

2011年，东京大学的 Tadashi Sugawara 在热水中创造了一个原始细胞。

molecules in various environments is critical for establishing the inventory of ingredients from which life originated on Earth, assuming that the abiotic production of molecules ultimately influenced the selection of molecules from which life emerged.<ref name="NASA strategy 2015"/>

Experimental research and computer modelling suggest that the surfaces of mineral particles inside hydrothermal vents have catalytic properties similar to those of enzymes and are able to create simple organic molecules, such as methanol (CH3OH) and formic, acetic and pyruvic acid out of the dissolved CO2 in the water.

实验研究和计算机模拟表明，热液喷口内的矿物颗粒表面具有与酶相似的催化性质，能够从溶解在水中的 CO 2 中生成简单的有机分子，如甲醇(CH 3 OH)和甲酸、乙酸和丙酮酸。

In 2019, scientists reported detecting, for the first time, [[Sugar|sugar molecules]], including [[ribose]], in [[meteorite]]s, suggesting that chemical processes on [[asteroid]]s can produce some fundamentally essential bio-ingredients important to [[life]], and supporting the notion of an [[RNA world]] prior to a DNA-based origin of life on Earth, and possibly, as well, the notion of [[panspermia]].<ref name="NASA-20191118">{{cite news |last1=Steigerwald |first1=Bill |last2=Jones |first2=Nancy |last3=Furukawa |first3=Yoshihiro |title=First Detection of Sugars in Meteorites Gives Clues to Origin of Life |url=https://www.nasa.gov/press-release/goddard/2019/sugars-in-meteorites |date=18 November 2019 |work=[[NASA]] |accessdate=18 November 2019 }}</ref><ref name="PNAS-20191113" />

The research reported above by Martin in 2016 supports the thesis that life arose at hydrothermal vents, that spontaneous chemistry in the Earth's crust driven by rock–water interactions at disequilibrium thermodynamically underpinned life's origin and that the founding lineages of the archaea and bacteria were H2-dependent autotrophs that used CO2 as their terminal acceptor in energy metabolism. Martin suggests, based upon this evidence that LUCA "may have depended heavily on the geothermal energy of the vent to survive".

马丁在2016年报告的上述研究支持了这样的论点: 生命起源于热液喷口; 在热力学不平衡状态下，由岩石-水相互作用驱动的地壳自发化学支撑了生命的起源; 古生菌和细菌的起源谱系是依赖于 h2的自养生物，它们在能量代谢中以 CO2为终端接受者。基于这些证据，Martin 认为 LUCA“可能严重依赖于喷口的地热能来生存”。

=== Chemical synthesis in the laboratory===

As early as the 1860s, experiments have demonstrated that biologically relevant molecules can be produced from interaction of simple carbon sources with abundant inorganic catalysts.

Mulkidjanian and co-authors think that the marine environments did not provide the ionic balance and composition universally found in cells, as well as of ions required by essential proteins and ribozymes found in virtually all living organisms, especially with respect to K+/Na+ ratio, Mn2+, Zn2+ and phosphate concentrations. The only known environments that mimic the needed conditions on Earth are found in terrestrial hydrothermal pools fed by steam vents. and depsipeptides, both by chemical reactions in the hydrothermal environment, as well as by exposure to UV light during transport from vents to adjacent pools. Their hypothesized pre-biotic environments are similar to the deep-oceanic vent environments most commonly hypothesized, but add additional components that help explain peculiarities found in reconstructions of the Last Universal Common Ancestor (LUCA) of all living organisms.

穆尔基贾尼亚及其合著者认为，海洋环境不能提供普遍存在于细胞中的离子平衡和组成，也不能提供几乎所有生物体中必需蛋白质和核酶所需的离子，特别是 k + /Na + 比值、 Mn 2 + 、 Zn < 2 + 和磷酸盐浓度。唯一模拟地球所需条件的已知环境是在由蒸汽喷口供应的陆地热液池中发现的。以及由于热液环境中的化学反应，以及在从喷口到邻近水池的运输过程中暴露在紫外线下而产生的缩肽。他们假设的生命出现之前的环境与最常见的假设的深海热液喷口环境相似，但是增加了一些额外的成分，这些成分有助于解释所有生物体的最后共同祖先(LUCA)重建过程中发现的特征。

====Fox proteinoids====

{{Main|Proteinoid}}

Colín-García et al. (2016) discuss the advantages and disadvantages of hydrothermal vents as primitive environments. Hoffmann suggests that volcanic ash may provide the many random shapes needed in the postulated complex nucleation event. This aspect of the theory can be tested experimentally.

Colín-García et al.(2016)讨论了热液喷口作为原始环境的优缺点。霍夫曼认为，火山灰可能提供了假定的复杂成核事件所需的许多随机形状。这方面的理论可以用实验来验证。

In trying to uncover the intermediate stages of abiogenesis mentioned by Bernal, [[Sidney W. Fox|Sidney Fox]] in the 1950s and 1960s studied the spontaneous formation of [[peptide]] structures (small chains of amino acids) under conditions that might plausibly have existed early in Earth's history. In one of his experiments, he allowed amino acids to dry out as if puddled in a warm, dry spot in prebiotic conditions: In an experiment to set suitable conditions for life to form, Fox collected volcanic material from a [[cinder cone]] in [[Hawaii]]. He discovered that the temperature was over 100 C just {{convert|4|in}} beneath the surface of the cinder cone, and suggested that this might have been the environment in which life was created—molecules could have formed and then been washed through the loose volcanic ash into the sea. He placed lumps of lava over amino acids derived from methane, ammonia and water, sterilized all materials, and baked the lava over the amino acids for a few hours in a glass oven. A brown, sticky substance formed over the surface, and when the lava was drenched in sterilized water, a thick, brown liquid leached out. He found that, as they dried, the amino acids formed long, often cross-linked, thread-like, submicroscopic [[Peptide|polypeptide]] molecules.<ref name="foxexp"/>

====Sugars====

In the 1970s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface. It is claimed that the discovery of microbial life below the surface of another body in our Solar System would lend significant credence to this theory. Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. Gold's theory is that the flow of such food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes (away from sedimentary carbon compounds) is that the organisms subsist on hydrogen released by an interaction between water and (reduced) iron compounds in rocks.

20世纪70年代，托马斯 · 戈尔德提出了这样一个理论: 生命最初不是在地球表面发展起来的，而是在地球表面以下几公里的地方。据称，在我们太阳系的另一个天体表面下发现微生物生命将为这一理论提供重要的证据。戈尔德还断言，生存需要从深处、遥不可及的地方获得的涓涓细流的食物，因为生活在有机物质水坑中的生命很可能会消耗掉所有的食物，从而灭绝。戈尔德的理论是，这种食物的流动是由于原始甲烷从地幔中释放出来; 对于深层微生物(远离沉积碳化合物)的食物供应，更为传统的解释是，这些生物靠岩石中水和(还原)铁化合物之间的相互作用释放出的氢维持生命。

In particular, experiments by [[Alexander Butlerov|Butlerov]] (the [[formose reaction]]) showed that tetroses, pentoses, and hexoses are produced when formaldehyde is heated under basic conditions with divalent metal ions like calcium. The reaction was scrutinized and subsequently proposed to be autocatalytic by Breslow in 1959.

====Nucleobases====

Zachary Adam claims that tidal processes that occurred during a time when the Moon was much closer may have concentrated grains of uranium and other radioactive elements at the high-water mark on primordial beaches, where they may have been responsible for generating life's building blocks. According to computer models, a deposit of such radioactive materials could show the same self-sustaining nuclear reaction as that found in the Oklo uranium ore seam in Gabon. Such radioactive beach sand might have provided sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. Radioactive monazite material also has released soluble phosphate into the regions between sand-grains, making it biologically "accessible." Thus amino acids, sugars, and soluble phosphates might have been produced simultaneously, according to Adam. Radioactive actinides, left behind in some concentration by the reaction, might have formed part of organometallic complexes. These complexes could have been important early catalysts to living processes.

扎卡里 · 亚当声称，在月球更接近地球的时候发生的潮汐过程可能使铀和其他放射性元素聚集在原始海滩的高水位标志处，在那里它们可能负责生成生命的组成部分。根据计算机模型，这种放射性物质的沉积可以显示出与加蓬奥克洛铀矿层中发现的相同的自我维持的核反应。这样的放射性海滩沙子可能提供了足够的能量来产生有机分子，如氨基酸和糖从乙腈在水中。放射性独居石材料还向沙粒之间的区域释放可溶性磷酸盐，使其在生物学上“可接近”因此，根据亚当的说法，氨基酸、糖和可溶性磷酸盐可能是同时产生的。放射性锕系元素是金属有机配合物的重要组成部分，在反应过程中会留下一定浓度的放射性锕系元素。这些配合物可能是生命过程的重要早期催化剂。

Similar experiments (see below) demonstrate that nucleobases like guanine and adenine could be synthesized from simple carbon and nitrogen sources like hydrogen cyanide and ammonia.

John Parnell has suggested that such a process could provide part of the "crucible of life" in the early stages of any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface. As the early Earth is thought to have had many smaller plates, it might have provided a suitable environment for such processes.

约翰 · 帕内尔认为，只要这颗行星足够大，足以形成一个将放射性矿物质带到地表的板块构造系统，这样一个过程就可以在任何早期潮湿的岩石行星的早期阶段提供部分“生命的熔炉”。由于早期地球被认为有许多较小的板块，它可能为这种过程提供了一个合适的环境。

[[Formamide]] produces all four ribonucleotides and other biological molecules when warmed in the presence of various terrestrial minerals. Formamide is ubiquitous in the Universe, produced by the reaction of water and [[hydrogen cyanide]] (HCN). It has several advantages as a biotic precursor, including the ability to easily become concentrated through the evaporation of water.<ref name="Saladino2012">{{cite journal |last1=Saladino |first1=Raffaele |last2=Crestini |first2=Claudia |last3=Pino |first3=Samanta |last4=Costanzo |first4=Giovanna |last5=Di Mauro |first5=Ernesto |display-authors=3 |date=March 2012 |title=Formamide and the origin of life. |journal=[[Physics of Life Reviews]] |volume=9 |issue=1 |pages=84–104 |bibcode=2012PhLRv...9...84S |doi=10.1016/j.plrev.2011.12.002 |pmid=22196896|hdl=2108/85168 |url=https://art.torvergata.it/bitstream/2108/85168/1/PoLRev%202012.pdf }}</ref><ref name="Saladino2012b">{{cite journal |last1=Saladino |first1=Raffaele |last2=Botta |first2=Giorgia |last3=Pino |first3=Samanta |last4=Costanzo |first4=Giovanna |last5=Di Mauro |first5=Ernesto |display-authors=3 |date=July 2012 |title=From the one-carbon amide formamide to RNA all the steps are prebiotically possible |journal=[[Biochimie]] |volume=94 |issue=7 |pages=1451–1456 |doi=10.1016/j.biochi.2012.02.018 |pmid=22738728}}</ref> Although HCN is poisonous, it only affects [[aerobic organism]]s ([[eukaryote]]s and aerobic bacteria), which did not yet exist. It can play roles in other chemical processes as well, such as the synthesis of the amino acid [[glycine]].<ref name="Follmann2009" />

In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and [[thymine]], have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like PAHs, the most carbon-rich chemical found in the Universe, may have been formed in [[red giant]] stars or in interstellar dust and gas clouds.<ref name="NASA-20150303">{{cite web |url=http://www.nasa.gov/content/nasa-ames-reproduces-the-building-blocks-of-life-in-laboratory |title=NASA Ames Reproduces the Building Blocks of Life in Laboratory |editor-last=Marlaire |editor-first=Ruth |date=3 March 2015 |work=Ames Research Center |publisher=NASA |location=Moffett Field, CA |accessdate=2015-03-05 |url-status=live |archiveurl=https://web.archive.org/web/20150305083306/http://www.nasa.gov/content/nasa-ames-reproduces-the-building-blocks-of-life-in-laboratory/ |archivedate=5 March 2015}}</ref> A group of Czech scientists reported that all four RNA-bases may be synthesized from formamide in the course of high-energy density events like extraterrestrial impacts.<ref>{{cite journal | last1 = Ferus | first1 = Martin | last2 = Nesvorný | first2 = David | last3 = Šponer | first3 = Jiří | last4 = Kubelík | first4 = Petr | last5 = Michalčíková | first5 = Regina | last6 = Shestivská | first6 = Violetta | last7 = Šponer | first7 = Judit E. | last8 = Civiš | first8 = Svatopluk | year = 2015 | title = High-energy chemistry of formamide: A unified mechanism of nucleobase formation | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 112 | issue = 3| pages = 657–662 | doi = 10.1073/pnas.1412072111 | pmid = 25489115 | bibcode = 2015PNAS..112..657F | pmc = 4311869 }}</ref>

Different forms of life with variable origin processes may have appeared quasi-simultaneously in the early history of Earth. The other forms may be extinct (having left distinctive fossils through their different biochemistry—e.g., hypothetical types of biochemistry). It has been proposed that:

在地球的早期历史中，具有不同起源过程的不同生命形式可能几乎同时出现。其他种类可能已经灭绝了(通过不同的生物化学方法留下了独特的化石，例如假定型生物化学)。有人建议:

====Use of high temperature====

<blockquote>The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoiesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore, the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.</blockquote>

第一批有机体是自我复制的富含铁的粘土，它们把二氧化碳固定成草酸和其他二羧酸。这种粘土及其代谢表型的复制系统进化到温泉富含硫化物的区域，获得了固氮的能力。最后磷酸盐被纳入进化系统，使核苷酸和磷脂的合成。如果生物合成要求生物生成，那么氨基酸的合成先于嘌呤和嘧啶碱的合成。此外，氨基酸硫酯聚合成多肽之前，由多核苷酸定向聚合氨基酸酯

In 1961, it was shown that the nucleic acid [[purine]] base [[adenine]] can be formed by heating aqueous [[ammonium cyanide]] solutions.<ref>{{cite journal |last=Oró |first=Joan |authorlink=Joan Oró |date=16 September 1961 |title=Mechanism of Synthesis of Adenine from Hydrogen Cyanide under Possible Primitive Earth Conditions |journal=Nature |volume=191 |issue=4794 |pages=1193–1194 |bibcode=1961Natur.191.1193O |doi=10.1038/1911193a0 |pmid=13731264|s2cid=4276712 }}</ref>

Metabolism-like reactions could have occurred naturally in early oceans, before the first organisms evolved. Metabolism may predate the origin of life, which may have evolved from the chemical conditions in the earliest oceans. Reconstructions in laboratories show that some of these reactions can produce RNA, and some others resemble two essential reaction cascades of metabolism: glycolysis and the pentose phosphate pathway, that provide essential precursors for nucleic acids, amino acids and lipids. A model for the origin of life using clay was forwarded by Alexander Cairns-Smith in 1985 and explored as a plausible mechanism by several scientists. The clay hypothesis postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in solution.

类似新陈代谢的反应可能在早期的海洋中自然发生，在第一个生物体进化之前。新陈代谢可能早于生命起源，而生命起源可能是从最早的海洋中的化学条件演化而来的。实验室的重建表明，其中一些反应可以产生 RNA，另外一些反应类似于代谢的两个基本反应级联: 糖酵解和磷酸戊糖途径，它们为核酸、氨基酸和脂类提供必需的前体。亚历山大 · 凯恩斯-史密斯在1985年提出了一个用粘土来描述生命起源的模型，并且几位科学家对其进行了合理的探索。粘土假说假设复杂的有机分子在溶液中硅酸盐晶体原有的非有机复制表面上逐渐形成。

====Use of low (freezing) temperature====

At the Rensselaer Polytechnic Institute, James Ferris' studies have also confirmed that montmorillonite clay minerals catalyze the formation of RNA in aqueous solution, by joining nucleotides to form longer chains.

在伦斯勒理工学院，James Ferris 的研究也证实了蒙脱石粘土矿物通过加入核苷酸形成更长的链来催化水溶液 RNA 的形成。

Other pathways for synthesizing bases from inorganic materials were also reported.<ref name="Basile1984">{{cite journal |last1=Basile |first1=Brenda |last2=Lazcano |first2=Antonio |authorlink2=Antonio Lazcano |last3=Oró |first3=Joan |year=1984 |title=Prebiotic syntheses of purines and pyrimidines |journal=[[Advances in Space Research]] |volume=4 |issue=12 |pages=125–131 |bibcode=1984AdSpR...4..125B |doi=10.1016/0273-1177(84)90554-4 |pmid=11537766}}</ref> Orgel and colleagues have shown that freezing temperatures are advantageous for the synthesis of purines, due to the concentrating effect for key precursors such as hydrogen cyanide.<ref>{{cite journal |last=Orgel |first=Leslie E. |date=August 2004 |title=Prebiotic Adenine Revisited: Eutectics and Photochemistry |journal=Origins of Life and Evolution of Biospheres |volume=34 |issue=4 |pages=361–369 |bibcode=2004OLEB...34..361O |doi=10.1023/B:ORIG.0000029882.52156.c2 |pmid=15279171|s2cid=4998122 }}</ref> Research by Miller and colleagues suggested that while adenine and [[guanine]] require freezing conditions for synthesis, [[cytosine]] and [[uracil]] may require boiling temperatures.<ref>{{cite journal |last1=Robertson |first1=Michael P. |last2=Miller |first2=Stanley L. |date=29 June 1995 |title=An efficient prebiotic synthesis of cytosine and uracil |journal=Nature |volume=375 |issue=6534 |pages=772–774 |bibcode=1995Natur.375..772R |doi=10.1038/375772a0 |pmid=7596408|s2cid=4351012 }}</ref> Research by the Miller group notes the formation of seven different amino acids and 11 types of [[nucleobase]]s in ice when ammonia and [[cyanide]] were left in a freezer from 1972 to 1997.<ref>{{cite journal |last=Fox |first=Douglas |date=February 2008 |url=http://discovermagazine.com/2008/feb/did-life-evolve-in-ice |title=Did Life Evolve in Ice? |journal=[[Discover (magazine)|Discover]] |accessdate=2008-07-03 |url-status=live |archiveurl=https://web.archive.org/web/20080630043228/http://discovermagazine.com/2008/feb/did-life-evolve-in-ice |archivedate=30 June 2008}}</ref><ref>{{cite journal |last1=Levy |first1=Matthew |last2=Miller |first2=Stanley L. |last3=Brinton |first3=Karen |last4=Bada |first4=Jeffrey L. |authorlink4=Jeffrey L. Bada |date=June 2000 |title=Prebiotic Synthesis of Adenine and Amino Acids Under Europa-like Conditions |journal=[[Icarus (journal)|Icarus]] |volume=145 |issue=2 |pages=609–613 |bibcode=2000Icar..145..609L |doi=10.1006/icar.2000.6365 |pmid=11543508}}</ref> Other work demonstrated the formation of s-[[triazine]]s (alternative nucleobases), [[pyrimidine]]s (including cytosine and uracil), and adenine from urea solutions subjected to freeze-thaw cycles under a reductive atmosphere (with spark discharges as an energy source).<ref>{{cite journal |last1=Menor-Salván |first1=César |last2=Ruiz-Bermejo |first2=Marta |last3=Guzmán |first3=Marcelo I. |last4=Osuna-Esteban |first4=Susana |last5=Veintemillas-Verdaguer |first5=Sabino |date=20 April 2009 |title=Synthesis of Pyrimidines and Triazines in Ice: Implications for the Prebiotic Chemistry of Nucleobases |journal=[[Chemistry: A European Journal]] |volume=15 |issue=17 |pages=4411–4418 |doi=10.1002/chem.200802656 |pmid=19288488}}</ref> The explanation given for the unusual speed of these reactions at such a low temperature is [[Eutectic system|eutectic freezing]]. As an ice crystal forms, it stays pure: only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often. Mechanistic exploration using quantum chemical methods provide a more detailed understanding of some of the chemical processes involved in chemical evolution, and a partial answer to the fundamental question of molecular biogenesis.<ref>{{cite journal |last1=Roy |first1=Debjani |last2=Najafian |first2=Katayoun |last3=von Ragué Schleyer |first3=Paul |authorlink3=Paul von Ragué Schleyer |date=30 October 2007 |title=Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=104 |issue=44 |pages=17272–17277 |bibcode=2007PNAS..10417272R |doi=10.1073/pnas.0708434104|pmc=2077245 |pmid=17951429}}</ref>

In 2007, Bart Kahr from the University of Washington and colleagues reported their experiments that tested the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate. "Mother" crystals with imperfections were cleaved and used as seeds to grow "daughter" crystals from solution. They then examined the distribution of imperfections in the new crystals and found that the imperfections in the mother crystals were reproduced in the daughters, but the daughter crystals also had many additional imperfections. For gene-like behavior to be observed, the quantity of inheritance of these imperfections should have exceeded that of the mutations in the successive generations, but it did not. Thus Kahr concluded that the crystals "were not faithful enough to store and transfer information from one generation to the next."

2007年，来自华盛顿大学的 Bart Kahr 和他的同事们报告了他们的实验，这些实验验证了晶体可以作为可转移信息的来源，使用邻苯二甲酸氢钾晶体。有缺陷的“母”晶体被切开，用作从溶液中生长“子”晶体的种子。然后他们检查了新晶体中缺陷的分布，发现母晶体中的缺陷在子晶体中重现，但子晶体也有许多其他的缺陷。对于观察到的类基因行为来说，这些缺陷的遗传数量应该已经超过了后代突变的数量，但事实并非如此。因此卡尔得出结论，这些晶体“不够忠实，不足以存储和传递信息从一代到下一代。”

====Use of less-reducing gas in Miller–Urey experiment====

At the time of the Miller–Urey experiment, scientific consensus was that the early Earth had a reducing atmosphere with compounds relatively rich in hydrogen and poor in oxygen (e.g., CH4 and NH3 as opposed to CO2 and [[nitrogen dioxide]] (NO2)). However, current scientific consensus describes the primitive atmosphere as either weakly reducing or neutral<ref name="Cleaves 2008">{{cite journal |last1=Cleaves |first1=H. James |last2=Chalmers |first2=John H. |last3=Lazcano |first3=Antonio |last4=Miller |first4=Stanley L. |last5=Bada |first5=Jeffrey L. |display-authors=3 |date=April 2008 |title=A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres |journal=Origins of Life and Evolution of Biospheres |volume=38 |issue=2 |pages=105–115 |bibcode=2008OLEB...38..105C |doi=10.1007/s11084-007-9120-3|pmid=18204914|s2cid=7731172 }}</ref><ref name="Chyba 2005">{{cite journal |last=Chyba |first=Christopher F. |s2cid=93303848 |date=13 May 2005 |title=Rethinking Earth's Early Atmosphere |journal=Science |volume=308 |issue=5724 |pages=962–963 |doi=10.1126/science.1113157 |pmid=15890865}}</ref> (see also [[Great Oxygenation Event|Oxygen Catastrophe]]). Such an atmosphere would diminish both the amount and variety of amino acids that could be produced, although studies that include [[iron]] and [[carbonate]] minerals (thought present in early oceans) in the experimental conditions have again produced a diverse array of amino acids.<ref name="Cleaves 2008" /> Other scientific research has focused on two other potential reducing environments: [[outer space]] and deep-sea thermal vents.<ref>{{harvnb|Barton|Briggs|Eisen|Goldstein|2007|pp=93–95}}</ref><ref>{{harvnb|Bada|Lazcano|2009|pp=56–57}}</ref><ref name="Bada 2003">{{cite journal |last1=Bada |first1=Jeffrey L. |last2=Lazcano |first2=Antonio |date=2 May 2003 |url=http://astrobiology.berkeley.edu/PDFs_articles/Bada_Science2003.pdf |title=Prebiotic Soup – Revisiting the Miller Experiment |journal=Science |volume=300 |issue=5620 |pages=745–746 |doi=10.1126/science.1085145 |pmid=12730584 |s2cid=93020326 |accessdate=2015-06-13 |url-status=live |archiveurl=https://web.archive.org/web/20160304222002/http://astrobiology.berkeley.edu/PDFs_articles/Bada_Science2003.pdf |archivedate=4 March 2016}}</ref>

====Synthesis based on hydrogen cyanide====

In the 1980s, Günter Wächtershäuser, encouraged and supported by Karl Popper, postulated his iron–sulfur world, a theory of the evolution of pre-biotic chemical pathways as the starting point in the evolution of life. It systematically traces today's biochemistry to primordial reactions which provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds.

20世纪80年代，根特·维奇特萧瑟在 Karl Popper 的鼓励和支持下，假设了他的铁硫世界---- 一个关于前生命化学路径进化的理论作为生命进化的起点。它系统地将今天的生物化学追溯到原始反应，这些原始反应为从简单的气体化合物合成有机构造块提供了可选的途径。

A research project completed in 2015 by [[John Sutherland (chemist)|John Sutherland]] and others found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, as well as those of RNA,<ref>{{cite news |last=Service |first=Robert F. |date=16 March 2015 |title=Researchers may have solved origin-of-life conundrum |url=http://news.sciencemag.org/biology/2015/03/researchers-may-have-solved-origin-life-conundrum |work=Science |type=News |location=Washington, D.C. |publisher=American Association for the Advancement of Science |accessdate=2015-07-26 |url-status=live |archiveurl=https://web.archive.org/web/20150812103559/http://news.sciencemag.org/biology/2015/03/researchers-may-have-solved-origin-life-conundrum |archivedate=12 August 2015}}</ref><ref name="patel">{{cite journal |last1=Patel |first1=Bhavesh H.|last2=Percivalle |first2=Claudia |last3=Ritson |first3=Dougal J. |last4=Duffy |first4=Colm D. |last5=Sutherland |first5=John D. |authorlink5=John Sutherland (chemist) |date=April 2015 |title=Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism |journal=[[Nature Chemistry]] |volume=7 |issue=4 |pages=301–307 |bibcode=2015NatCh...7..301P |doi=10.1038/nchem.2202 |pmid=25803468 |ref=harv |pmc=4568310}}</ref> while not producing a wide range of other compounds.<ref>{{harvnb|Patel|Percivalle|Ritson|Duffy|2015|p=302}}</ref> The researchers used the term "cyanosulfidic" to describe this network of reactions.<ref name="patel" />

In contrast to the classical Miller experiments, which depend on external sources of energy (simulated lightning, ultraviolet irradiation), "Wächtershäuser systems" come with a built-in source of energy: sulfides of iron (iron pyrite) and other minerals. The energy released from redox reactions of these metal sulfides is available for the synthesis of organic molecules, and such systems may have evolved into autocatalytic sets constituting self-replicating, metabolically active entities predating the life forms known today.

经典的米勒实验依赖于外部能源(模拟闪电、紫外线照射) ，与此相反，“韦切特修斯系统”内置了能源: 铁(黄铁矿)和其他矿物的硫化物。这些金属硫化物的氧化还原反应所释放的能量可用于合成有机分子，这种系统可能已经演变成自我复制的、新陈代谢活跃的实体，早于今天已知的生命形式。

====Issues during laboratory synthesis====

The spontaneous formation of complex polymers from abiotically generated monomers under the conditions posited by the "soup" theory is not at all a straightforward process. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were also formed in high concentration during the Miller–Urey and [[Joan Oró]] experiments.<ref>{{cite journal |last1=Oró |first1=Joan |last2=Kimball |first2=Aubrey P. |date=February 1962 |title=Synthesis of purines under possible primitive earth conditions: II. Purine intermediates from hydrogen cyanide |journal=[[Archives of Biochemistry and Biophysics]] |volume=96 |issue=2 |pages=293–313 |doi=10.1016/0003-9861(62)90412-5 |pmid=14482339}}</ref> The Miller–Urey experiment, for example, produces many substances that would react with the amino acids or terminate their coupling into peptide chains.<ref>{{cite book |editor-last=Ahuja |editor-first=Mukesh |year=2006 |chapter=Origin of Life |chapterurl=https://books.google.com/books?id=VJF12TlT58kC&pg=PA11 |title=Life Science |volume=1 |location=Delhi |publisher=Isha Books |page=11 |isbn=978-81-8205-386-1 |oclc=297208106 |ref=harv}}{{Unreliable source?|reason=What material is Ahuja editing? Further, see use of Ahuja material in the Iron-sulfur world section in this WP article, among others. See also: Wikipedia talk:Noticeboard for India-related topics/Archive 42#Problem with ISHA books as references|date=June 2015}}</ref>

Several models reject the self-replication of a "naked-gene", postulating instead the emergence of a primitive metabolism providing a safe environment for the later emergence of RNA replication. The centrality of the Krebs cycle (citric acid cycle) to energy production in aerobic organisms, and in drawing in carbon dioxide and hydrogen ions in biosynthesis of complex organic chemicals, suggests that it was one of the first parts of the metabolism to evolve. Concordantly, geochemist Russell has proposed that "the purpose of life is to hydrogenate carbon dioxide" (as part of a "metabolism-first," rather than a "genetics-first," scenario). Physicist Jeremy England has proposed that life was inevitable from general thermodynamic considerations: <blockquote>... when a group of atoms is driven by an external source of energy (like the sun or chemical fuel) and surrounded by a heat bath (like the ocean or atmosphere), it will often gradually restructure itself in order to dissipate increasingly more energy. This could mean that under certain conditions, matter inexorably acquires the key physical attribute associated with life.</blockquote>

一些模型拒绝接受“裸基因”的自我复制，而是假定原始代谢的出现为后来 RNA 复制的出现提供了一个安全的环境。克雷布斯循环在需氧生物的能量生产中的中心地位，以及在复杂有机化学物质的生物合成中吸收二氧化碳和氢离子的中心三羧酸循环，表明它是代谢进化的最初部分之一。地球化学家罗素一致提出，“生命的目的是氢化二氧化碳”(作为“代谢优先”的一部分，而不是“遗传优先”的设想)。物理学家杰里米 · 英格兰提出，从一般的热力学考虑来看，生命是不可避免的... ... 当一组原子受到外部能源(如太阳或化学燃料)的驱动，并被热浴(如海洋或大气)包围时，它往往会逐渐重组自己，以便耗散越来越多的能量。这可能意味着在某些条件下，物质无情地获得了与生命相关的关键物理属性

=== Autocatalysis ===

One of the earliest incarnations of this idea was put forward in 1924 with Oparin's notion of primitive self-replicating vesicles which predated the discovery of the structure of DNA. Variants in the 1980s and 1990s include Wächtershäuser's iron–sulfur world theory and models introduced by Christian de Duve based on the chemistry of thioesters. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by Freeman Dyson in the early 1980s and Stuart Kauffman's notion of collectively autocatalytic sets, discussed later that decade.

这个概念最早的化身之一是在1924年提出的，奥帕林的原始自我复制囊泡的概念早于 DNA 结构的发现。20世纪80年代和90年代的变体包括韦切特修斯的铁硫世界理论和克里斯汀·德·迪夫基于硫酯化学引入的模型。更为抽象和理论化的论点，为新陈代谢的出现没有基因的存在的合理性，包括弗里曼 · 戴森在20世纪80年代早期提出的数学模型和斯图尔特 · 考夫曼的集体自催化集的概念，在那个十年后期讨论。

{{Main|Autocatalysis}}

[[Autocatalysis|Autocatalysts]] are substances that catalyze the production of themselves and therefore are "molecular replicators." The simplest self-replicating chemical systems are autocatalytic, and typically contain three components: a product molecule and two precursor molecules. The product molecule joins together the precursor molecules, which in turn produce more product molecules from more precursor molecules. The product molecule catalyzes the reaction by providing a complementary template that binds to the precursors, thus bringing them together. Such systems have been demonstrated both in biological [[macromolecule]]s and in small organic molecules.<ref name="Paul2004">{{cite journal |last1=Paul |first1=Natasha |last2=Joyce |first2=Gerald F. |date=December 2004 |title=Minimal self-replicating systems |journal=Current Opinion in Chemical Biology |volume=8 |issue=6 |pages=634–639 |doi=10.1016/j.cbpa.2004.09.005|pmid=15556408}}</ref><ref name="Bissette2013">{{cite journal |last1=Bissette |first1=Andrew J. |last2=Fletcher |first2=Stephen P. |date=2 December 2013 |title=Mechanisms of Autocatalysis |journal=Angewandte Chemie International Edition |volume=52 |issue=49 |pages=12800–12826 |doi=10.1002/anie.201303822 |pmid=24127341}}</ref> Systems that do not proceed by template mechanisms, such as the self-reproduction of [[micelle]]s and [[Vesicle (biology and chemistry)|vesicles]], have also been observed.<ref name="Bissette2013" />

Orgel summarized his analysis by stating, <blockquote>There is at present no reason to expect that multistep cycles such as the reductive citric acid cycle will self-organize on the surface of FeS/FeS2 or some other mineral."</blockquote> It is possible that another type of metabolic pathway was used at the beginning of life. For example, instead of the reductive citric acid cycle, the "open" acetyl-CoA pathway (another one of the five recognized ways of carbon dioxide fixation in nature today) would be compatible with the idea of self-organization on a metal sulfide surface. The key enzyme of this pathway, carbon monoxide dehydrogenase/acetyl-CoA synthase, harbors mixed nickel-iron-sulfur clusters in its reaction centers and catalyzes the formation of acetyl-CoA (similar to acetyl-thiol) in a single step. There are increasing concerns, however, that prebiotic thiolated and thioester compounds are thermodynamically and kinetically unfavorable to accumulate in presumed prebiotic conditions (i.e. hydrothermal vents). It has also been proposed that cysteine and homocysteine may have reacted with nitriles resulting from the Stecker reaction, readily forming catalytic thiol-reach poplypeptides.

奥格尔总结了他的分析，他说: 目前没有理由期望多步循环，例如还原三羧酸循环在 FeS/FeS 2 或其他矿物的表面上会自组织。很有可能另一种类型的代谢途径在生命的开始就被使用了。例如，“开放的”乙酰辅酶 a 途径(今天在自然界中被认可的另一种固定二氧化碳的途径)取代了还原性的三羧酸循环，这种途径与自我组织在金属硫化物表面的想法是一致的。该途径的关键酶一氧化碳脱氢酶/乙酰辅酶 a 合成酶在其反应中心存在镍铁硫混合簇，并在一步反应中催化乙酰辅酶 a (类似于乙酰巯基)的形成。然而，人们越来越关注的是，生命之前的硫代化合物和硫代酯化合物在热力学和动力学上都不适合在假定的生命之前的条件下积累(即:。热液喷口)。还有人提出，半胱氨酸和同型半胱氨酸可能通过 Stecker 反应与腈反应，很容易形成催化巯基化的肽。

It has been proposed that life initially arose as autocatalytic chemical networks.<ref>{{harvnb|Kauffman|1993|loc=chpt. 7}}</ref> British [[ethologist]] [[Richard Dawkins]] wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book ''[[The Ancestor's Tale]]''.<ref>{{harvnb|Dawkins|2004}}</ref> In his book, Dawkins cites experiments performed by [[Julius Rebek]] and his colleagues in which they combined amino adenosine and [[pentafluorophenyl esters]] with the autocatalyst amino adenosine triacid ester (AATE). One product was a variant of AATE, which catalyzed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.<ref>{{cite journal |last1=Tjivikua |first1=T. |last2=Ballester |first2=Pablo |last3=Rebek |first3=Julius Jr. |authorlink3=Julius Rebek |date=January 1990 |title=Self-replicating system |journal=[[Journal of the American Chemical Society]] |volume=112 |issue=3 |pages=1249–1250 |doi=10.1021/ja00159a057 }}</ref><ref>{{cite news |last=Browne |first=Malcolm W. |authorlink=Malcolm Browne |date=30 October 1990 |title=Chemists Make Molecule With Hint of Life |url=https://www.nytimes.com/1990/10/30/science/chemists-make-molecule-with-hint-of-life.html |newspaper=The New York Times |location=New York |accessdate=2015-07-14 |url-status=live |archiveurl=https://web.archive.org/web/20150721135740/http://www.nytimes.com/1990/10/30/science/chemists-make-molecule-with-hint-of-life.html |archivedate=21 July 2015}}</ref>

The zinc world (Zn-world) theory of Mulkidjanian is an extension of Wächtershäuser's pyrite hypothesis. Wächtershäuser based his theory of the initial chemical processes leading to informational molecules (RNA, peptides) on a regular mesh of electric charges at the surface of pyrite that may have facilitated the primeval polymerization by attracting reactants and arranging them appropriately relative to each other. The Zn-world theory specifies and differentiates further. Hydrothermal fluids rich in H2S interacting with cold primordial ocean (or Darwin's "warm little pond") water leads to the precipitation of metal sulfide particles. Oceanic vent systems and other hydrothermal systems have a zonal structure reflected in ancient volcanogenic massive sulfide deposits (VMS) of hydrothermal origin. They reach many kilometers in diameter and date back to the Archean Eon. Most abundant are pyrite (FeS2), chalcopyrite (CuFeS2), and sphalerite (ZnS), with additions of galena (PbS) and alabandite (MnS). ZnS and MnS have a unique ability to store radiation energy, e.g. from UV light. During the relevant time window of the origins of replicating molecules, the primordial atmospheric pressure was high enough (>100 bar, about 100 atmospheres) to precipitate near the Earth's surface, and UV irradiation was 10 to 100 times more intense than now; hence the unique photosynthetic properties mediated by ZnS provided just the right energy conditions to energize the synthesis of informational and metabolic molecules and the selection of photostable nucleobases.

穆尔基贾尼亚的锌世界理论是韦切特修斯的黄铁矿假说的延伸。Wächtershäuser 将导致信息分子(RNA，肽)的初始化学过程的理论建立在黄铁矿表面规则网状的电荷上，这些电荷可能通过吸引反应物并将它们相互适当地排列来促进原始聚合。锌世界理论进一步明确和区分了这一问题。热液中富含 h 2 s 与冷原始海洋(或达尔文的“温暖的小池塘”)水相互作用，导致金属硫化物颗粒的沉淀。大洋热液系统和其他热液系统具有带状结构，反映在古火山成因的热液块状硫化物矿床(VMS)中。它们的直径可达数公里，可以追溯到太古宙。黄铁矿(FeS 2 )、黄铜矿(CuFeS 2 )和闪锌矿(ZnS)最为丰富，其次是方铅矿(PbS)和阿拉巴班特矿(MnS)。ZnS 和 MnS 具有独特的存储辐射能的能力，例如:。来自紫外线。在复制分子起源的相关时间窗口期间，原始大气压力高到足以在地球表面附近沉淀，紫外线辐射强度是现在的10至100倍; 因此，硫化锌介导的独特光合特性提供了恰到好处的能量条件，为信息分子和新陈代谢分子的合成以及光稳定核酸酶的选择提供能量。

== Encapsulation: morphology ==

{{see also|Evolution of cells}}

The Zn-world theory has been further filled out with experimental and theoretical evidence for the ionic constitution of the interior of the first proto-cells before archaea, bacteria and proto-eukaryotes evolved. Archibald Macallum noted the resemblance of body fluids such as blood and lymph to seawater; however, the inorganic composition of all cells differ from that of modern seawater, which led Mulkidjanian and colleagues to reconstruct the "hatcheries" of the first cells combining geochemical analysis with phylogenomic scrutiny of the inorganic ion requirements of universal components of modern cells. The authors conclude that ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K+, Zn2+, Mn2+, and . Geochemical reconstruction shows that the ionic composition conducive to the origin of cells could not have existed in what we today call marine settings but is compatible with emissions of vapor-dominated zones of what we today call inland geothermal systems. Under the oxygen depleted, CO2-dominated primordial atmosphere, the chemistry of water condensates and exhalations near geothermal fields would resemble the internal milieu of modern cells. Therefore, the precellular stages of evolution may have taken place in shallow "Darwin ponds" lined with porous silicate minerals mixed with metal sulfides and enriched in K+, Zn2+, and phosphorus compounds.

在古细菌、细菌和原真核生物进化之前，第一原细胞内部的离子组成的实验和理论证据进一步充实了 Zn-world 理论。阿奇博尔德 · 马卡勒姆指出，体液如血液和淋巴液与海水的相似性; 然而，所有细胞的无机成分与现代海水的不同，这促使穆尔基德詹尼安和同事们重建了第一批细胞的“孵化室” ，结合地球化学分析和现代细胞普遍成分的无机离子需求的基因组分析。结果表明，蛋白质和功能系统对 k + 、 Zn 2 + 、 Mn 2 + 、 Zn 2 + 具有亲和力和功能需求。地球化学重建表明，有利于细胞起源的离子组成不可能存在于我们今天所说的海洋环境中，而是与我们今天所说的内陆地热系统的蒸汽主导区域的排放相一致。在耗氧、 CO < 亚 < 2 </亚 > 的原始大气条件下，地热场附近水凝析和呼出的化学反应类似于现代细胞的内部环境。因此，在含多孔硅酸盐矿物与金属硫化物混合并富集于 k + 、 Zn 2 + 和磷化合物的浅“ Darwin 池”中，可能发生了细胞演化的精确阶段。

=== Encapsulation without a membrane ===

We define a scenario as a set of related concepts pertinent to the origin of life that is or has been investigated. The concepts related to the Iron-Sulfur world can be considered as a scenario. We consider some other scenarios that may partially overlap with scenarios discussed above or with each other.

我们将场景定义为一组与已经或者已经被研究过的生命起源相关的概念。与铁硫世界有关的概念可以看作是一种情景。我们考虑一些可能与上面讨论的场景部分重叠或相互重叠的其他场景。

====Oparin's coacervate====

====Membraneless polyester droplets====

In September 2020, chemists described, for the first time, possible chemical pathways from nonliving prebiotic chemicals to complex biochemicals that could give rise to living organisms, based on a new computer program named ALLCHEMY.

2020年9月，化学家们基于一个名为 ALLCHEMY 的新计算机程序，首次描述了可能的化学途径，从非生命起源的化学物质到可能产生生命机体的复杂生物化学物质。

Researchers Tony Jia and Kuhan Chandru<ref>{{cite journal |last1=Jia |first1=Tony Z. |last2=Chandru |first2=Kuhan |last3=Hongo |first3=Yayoi |last4=Afrin |first4=Rehana |last5=Usui |first5=Tomohiro |last6=Myojo |first6=Kunihiro |last7=Cleaves |first7=H. James |title=Membraneless polyester microdroplets as primordial compartments at the origins of life |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=32 |date=22 July 2019 |pages=15830–15835 |doi=10.1073/pnas.1902336116|pmid=31332006 |pmc=6690027 }}</ref> have proposed that membraneless polyesters droplets could have been significant in the Origins of Life.<ref>{{Cite journal|last1=Chandru|first1=Kuhan|last2=Mamajanov|first2=Irena|last3=Cleaves|first3=H. James|last4=Jia|first4=Tony Z.|date=January 2020|title=Polyesters as a Model System for Building Primitive Biologies from Non-Biological Prebiotic Chemistry|journal=Life|language=en|volume=10|issue=1|pages=6|doi=10.3390/life10010006|pmc=7175156|pmid=31963928}}</ref> Given the "messy" nature of prebiotic chemistry,<ref>{{cite web |last1=Marc |first1=Kaufman |title=NASA Astrobiology |url=https://astrobiology.nasa.gov/news/messy-chemistry-a-new-way-to-approach-the-origins-of-life/|date = 18 July 2019 |website=astrobiology.nasa.gov |language=en-EN}}</ref><ref>{{cite journal |last1=Guttenberg |first1=Nicholas |last2=Virgo |first2=Nathaniel |last3=Chandru |first3=Kuhan |last4=Scharf |first4=Caleb |last5=Mamajanov |first5=Irena |title=Bulk measurements of messy chemistries are needed for a theory of the origins of life |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |date=13 November 2017 |volume=375 |issue=2109 |pages=20160347 |doi=10.1098/rsta.2016.0347|pmid=29133446 |pmc=5686404 |bibcode=2017RSPTA.37560347G }}</ref> the spontaneous generation of these combinatorial droplets may have played a role in early cellularization before the innovation of lipid vesicles. Protein function within and RNA function in the presence of certain polyester droplets was shown to be preserved within the droplets. Additionally, the droplets have scaffolding ability, by allowing lipids to assemble around them that may have prevented leakage of genetic materials.

=== Proteinoid microspheres ===

In the early 1970s, Manfred Eigen and Peter Schuster examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup. In a hypercycle, the information storing system (possibly RNA) produces an enzyme, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery of ribozymes capable of catalyzing their own chemical reactions. The hypercycle theory requires the existence of complex biochemicals, such as nucleotides, which do not form under the conditions proposed by the Miller–Urey experiment.

在20世纪70年代早期，曼弗雷德 · 埃根和彼得 · 舒斯特研究了生命前汤中介于分子混沌和自我复制超循环之间的短暂阶段。在超循环中，信息存储系统(可能是 RNA)产生一种酶，这种酶按顺序催化另一个信息系统的形成，直到最后一个信息系统的产物帮助形成第一个信息系统。经过数学处理，超循环可以产生准种类，通过自然选择进入达尔文进化的形式。超循环理论的推动力是发现了能够催化自身化学反应的核酶。超循环理论需要复杂的生物化学物质的存在，比如核苷酸，它们不是在 Miller-Urey 实验提出的条件下形成的。

Fox observed in the 1960s that the proteinoids that he had synthesized could form cell-like structures that have been named "[[Proteinoid|proteinoid microspheres]]".<ref name="foxexp">{{cite web |url=http://nitro.biosci.arizona.edu/courses/EEB105/lectures/Origins_of_Life/origins.html |title=Part 4: Experimental studies of the origins of life |last=Walsh |first=J. Bruce |year=1995 |work=Origins of life |publisher=[[University of Arizona]] |location=Tucson, AZ |type=Lecture notes |archiveurl=https://web.archive.org/web/20080113152408/http://nitro.biosci.arizona.edu/courses/EEB105/lectures/Origins_of_Life/origins.html |archivedate=2008-01-13 |accessdate=2015-06-08}}</ref>

The amino acids had combined to form [[proteinoid]]s, and the proteinoids had combined to form small globules that Fox called "microspheres". His proteinoids were not cells, although they formed clumps and chains reminiscent of [[cyanobacteria]], but they contained no functional [[nucleic acid]]s or any encoded information. Based upon such experiments, [[Colin Pittendrigh]] stated in 1967 that "laboratories will be creating a living cell within ten years," a remark that reflected the typical contemporary naivety about the complexity of cell structures.<ref>{{harvnb|Woodward|1969|p=287}}</ref>

In his "Thermodynamic Dissipation Theory of the Origin and Evolution of Life", Karo Michaelian has taken the insight of Boltzmann and the work of Prigogine to its ultimate consequences regarding the origin of life. This theory postulates that the hallmark of the origin and evolution of life is the microscopic dissipative structuring of organic pigments and their proliferation over the entire Earth surface. In fact, not only RNA and DNA, but many fundamental molecules of life (those common to all three domains of life) are also pigments that absorb in the UV-C, and many of these also have a chemical affinity to RNA and DNA. Nucleic acids may thus have acted as acceptor molecules to the UV-C photon excited antenna pigment donor molecules by providing an ultrafast channel for dissipation. Michaelian has shown using the formalism of non-linear irreversible thermodynamics that there would have existed during the Archean a thermodynamic imperative to the abiogenic UV-C photochemical synthesis and proliferation of these pigments over the entire Earth surface if they acted as catalysts to augment the dissipation of the solar photons. By the end of the Archean, with life-induced ozone dissipating UV-C light in the Earth's upper atmosphere, it would have become ever more improbable for a completely new life to emerge that did not rely on the complex metabolic pathways already existing since now the free energy in the photons arriving at Earth's surface would have been insufficient for direct breaking and remaking of covalent bonds. It has been suggested, however, that such changes in the surface flux of ultraviolet radiation due to geophysical events affecting the atmosphere could have been what promoted the development of complexity in life based on existing metabolic pathways, for example during the Cambrian explosion

在他的“生命起源和进化的热力学耗散理论”中，Karo Michaelian 将波尔兹曼的洞察力和 Prigogine 的工作带到了关于生命起源的最终结果。这个理论假定生命起源和进化的标志是有机色素的微观耗散结构及其在整个地球表面的扩散。事实上，不仅仅是 RNA 和 DNA，还有许多生命的基本分子(这些都是生命的三个领域所共有的)也是紫外线 c 吸收的色素，而且其中许多也对 RNA 和 DNA 有化学亲和力。因此，核酸可能作为受体分子对 UV-C 光子激发的天线色素供体分子提供了一个超快的消散通道。米歇尔利用非线性不可逆热力学的公式表明，如果这些色素作为催化剂来增加太阳光子的耗散，那么在太古宙期间，这些色素在整个地球表面上的无机生成的 UV-C 光化学合成和增殖就具有热力学上的必然性。到太古宙结束时，由于生命引起的臭氧消散了地球上层大气中的 UV-C 光线，因此，如果不依赖已经存在的复杂的新陈代谢途径，那么一种全新的生命就更不可能出现，因为现在到达地球表面的光子中的自由能量不足以直接破坏和重新形成共价键。然而，有人认为，由于影响大气层的地球物理事件导致的紫外线辐射表面通量的这种变化，可能促进了基于现有代谢途径的生命复杂性的发展，例如在寒武纪大爆发期间

=== Lipid world ===

Some of the most difficult problems concerning the origin of life, such as enzyme-less replication of RNA and DNA, homochirality of the fundamental molecules, and the origin of information encoding in RNA and DNA, also find an explanation within the same dissipative thermodynamic framework by considering the probable existence of a relation between primordial replication and UV-C photon dissipation. Michaelian suggests that it is erroneous to expect to describe the emergence, proliferation, or even evolution, of life without overwhelming reference to entropy production through the dissipation of a generalized thermodynamic potential, in particular, the prevailing solar photon flux.

关于生命起源的一些最困难的问题，如 RNA 和 DNA 的无酶复制、基本分子的同手性以及 RNA 和 DNA 中编码信息的起源，也在同一耗散热力学框架内得到解释，考虑到原始复制和 UV-C 光子耗散之间可能存在一种关系。认为，期望通过广义的产生熵热动力位能的耗散来描述生命的出现、增殖，甚至是进化，而不以压倒性的参考来描述生命是错误的，特别是流行的太阳光子通量。

{{Main|Gard model}}

The [[Gard model|lipid world]] theory postulates that the first self-replicating object was [[lipid]]-like.<ref>{{cite web |url=http://www.weizmann.ac.il/molgen/Lancet/research/prebiotic-evolution |title=Systems Prebiology-Studies of the origin of Life |last=Lancet |first=Doron |date=30 December 2014 |website=The Lancet Lab |publisher=Department of Molecular Genetics; [[Weizmann Institute of Science]] |location=Rehovot, Israel |accessdate=2015-06-26 |url-status=live |archiveurl=https://web.archive.org/web/20150626180507/http://www.weizmann.ac.il/molgen/Lancet/research/prebiotic-evolution |archivedate=26 June 2015}}</ref><ref>{{cite journal |last1=Segré |first1=Daniel |last2=Ben-Eli |first2=Dafna |last3=Deamer |first3=David W. |last4=Lancet |first4=Doron |date=February 2001 |title=The Lipid World |url=http://www.weizmann.ac.il/molgen/Lancet/sites/molgen.Lancet/files/uploads/segre_lipid_world.pdf |journal=Origins of Life and Evolution of the Biosphere |volume=31 |issue=1–2 |pages=119–145 |doi=10.1023/A:1006746807104 |pmid=11296516 |bibcode=2001OLEB...31..119S |s2cid=10959497 |accessdate=2008-09-11 |url-status=live |archiveurl=https://web.archive.org/web/20150626225745/http://www.weizmann.ac.il/molgen/Lancet/sites/molgen.Lancet/files/uploads/segre_lipid_world.pdf |archivedate=26 June 2015}}</ref> It is known that phospholipids form [[lipid bilayer]]s in water while under agitation—the same structure as in cell membranes. These molecules were not present on early Earth, but other [[Amphiphile|amphiphilic]] long-chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two [[Offspring|progenies]]. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favourably. Studies on vesicles from potentially prebiotic amphiphiles have so far been limited to systems containing one or two types of amphiphiles. This in contrast to the output of simulated prebiotic chemical reactions, which typically produce very heterogeneous mixtures of compounds.<ref name="Chen 2010" />

Within the hypothesis of a lipid bilayer membrane composed of a mixture of various distinct amphiphilic compounds there is the opportunity of a huge number of theoretically possible combinations in the arrangements of these amphiphiles in the membrane. Among all these potential combinations, a specific local arrangement of the membrane would have favoured the constitution of a hypercycle,<ref>{{cite journal |last1=Eigen |first1=Manfred |authorlink1=Manfred Eigen |last2=Schuster |first2=Peter |authorlink2=Peter Schuster |date=November 1977 |title=The Hypercycle. A Principle of Natural Self-Organization. Part A: Emergence of the Hypercycle |url=http://jaguar.biologie.hu-berlin.de/~wolfram/pages/seminar_theoretische_biologie_2007/literatur/schaber/Eigen1977Naturwissenschaften64.pdf |journal=Naturwissenschaften |volume=64 |issue=11 |pages=541–65|bibcode=1977NW.....64..541E |doi=10.1007/bf00450633 |pmid=593400 |accessdate=2015-06-13 |url-status=dead |archiveurl=https://web.archive.org/web/20160303194728/http://jaguar.biologie.hu-berlin.de/~wolfram/pages/seminar_theoretische_biologie_2007/literatur/schaber/Eigen1977Naturwissenschaften64.pdf |archivedate=3 March 2016}}

A new origin-of-life theory based on self-replicating beta-sheet structures has been put forward by Maury in 2009. The theory suggest that self-replicating and self-assembling catalytic amyloids were the first informational polymers in a primitive pre-RNA world. The main arguments for the amyloid hypothesis is based on the structural stability, autocatalytic and catalytic properties, and evolvability of beta-sheet based informational systems. Such systems are also error correcting and chiroselective.

Maury 于2009年提出了一种新的生命起源理论，该理论基于自我复制的 beta-sheet 结构。这一理论表明，自我复制和自我组装催化淀粉样蛋白是原始前 rna 世界中最早的信息聚合物。淀粉样蛋白假说的主要论据是基于 β- 表信息系统的结构稳定性、自催化和催化特性以及可进化性。这样的系统也是错误纠正和脊椎选择性。

* {{cite journal |last1=Eigen |first1=Manfred |last2=Schuster |first2=Peter |year=1978 |title=The Hypercycle. A Principle of Natural Self-Organization. Part B: The Abstract Hypercycle |url=http://jaguar.biologie.hu-berlin.de/~wolfram/pages/seminar_theoretische_biologie_2007/literatur/schaber/Eigen1978Naturwissenschaften65a.pdf |journal=Naturwissenschaften |volume=65 |issue=1 |pages=7–41 |bibcode=1978NW.....65....7E |doi=10.1007/bf00420631 |s2cid=1812273 |accessdate=2015-06-13 |url-status=dead |archiveurl=https://web.archive.org/web/20160303203325/http://jaguar.biologie.hu-berlin.de/~wolfram/pages/seminar_theoretische_biologie_2007/literatur/schaber/Eigen1978Naturwissenschaften65a.pdf |archivedate=3 March 2016}}



< ! ——在添加足够的内容之后，可能分离出的子部分: 与 rna 世界和蛋白质合成进化有关的证据 >

* {{cite journal |last1=Eigen |first1=Manfred |last2=Schuster |first2=Peter |date=July 1978 |title=The Hypercycle. A Principle of Natural Self-Organization. Part C: The Realistic Hypercycle |url=http://jaguar.biologie.hu-berlin.de/~wolfram/pages/seminar_theoretische_biologie_2007/literatur/schaber/Eigen1978Naturwissenschaften65b.pdf |journal=Naturwissenschaften |volume=65 |issue=7 |pages=341–369 |bibcode=1978NW.....65..341E |doi=10.1007/bf00439699 |s2cid=13825356 |accessdate=2015-06-13 |url-status=dead |archiveurl=https://web.archive.org/web/20160616180402/http://jaguar.biologie.hu-berlin.de/~wolfram/pages/seminar_theoretische_biologie_2007/literatur/schaber/Eigen1978Naturwissenschaften65b.pdf |archivedate=16 June 2016}}</ref><ref>{{cite journal |last1=Markovitch |first1=Omer |last2=Lancet |first2=Doron |date=Summer 2012 |title=Excess Mutual Catalysis Is Required for Effective Evolvability |journal=[[Artificial Life (journal)|Artificial Life]] |volume=18 |issue=3 |pages=243–266 |doi=10.1162/artl_a_00064|pmid=22662913 |s2cid=5236043 }}</ref> actually a positive [[feedback]] composed of two mutual catalysts represented by a membrane site and a specific compound trapped in the vesicle. Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct [[Lineage (evolution)|lineages]] of vesicles which would have allowed Darwinian natural selection.<ref>{{cite journal |last=Tessera |first=Marc |year=2011 |title=Origin of Evolution ''versus'' Origin of Life: A Shift of Paradigm |journal=[[International Journal of Molecular Sciences]] |volume=12 |issue=6 |pages=3445–3458 |doi=10.3390/ijms12063445 |pmc=3131571 |pmid=21747687}} Special Issue: "Origin of Life 2011"</ref>

=== Protocells ===

Theories of abiogenesis seldom address the caveat raised by Harold Blum: if the key informational elements of life – proto-nucleic acid chains – spontaneously form duplex structures, then there is no way to dissociate them. <blockquote>Somewhere in this cycle work must be done, which means that free energy must be expended. If the parts assemble themselves on a template spontaneously, work has to be done to take the replica off; or, if the replica comes off the template of its own accord, work must be done to put the parts on in the first place.</blockquote>

无机生成理论很少解决 Harold Blum 提出的问题: 如果生命的关键信息元素——原核酸链——自发地形成双重结构，那么就没有办法分离它们。在这个循环的某个地方必须做功，这意味着自由能必须被消耗。如果这些部件自发地在模板上组装起来，就必须做工作把复制品拿下来; 或者，如果复制品自动脱离模板，就必须做工作把这些部件放在首位。</blockquote >

{{Main|Protocell}}

[[File:Phospholipids aqueous solution structures.svg|thumb|upright|The three main structures [[phospholipid]]s form spontaneously in solution: the [[liposome]] (a closed bilayer), the [[micelle]] and the bilayer.]]

The Oparin–Haldane conjecture addresses the formation, but not the dissociation, of nucleic acid polymers and duplexes. However, nucleic acids are unusual because, in the absence of counterions (low salt) to neutralize the high charges on opposing phosphate groups, the nucleic acid duplex dissociates into single chains. Early tides, driven by a close moon, could have generated rapid cycles of dilution (high tide, low salt) and concentration (dry-down at low tide, high salt) that exclusively promoted the replication of nucleic acids This theory has been criticized on the grounds that early tides may not have been so rapid, although regression from current values requires an Earth–Moon juxtaposition at around two Ga, for which there is no evidence, and early tides may have been approximately every seven hours. Another critique is that only 2–3% of the Earth's crust may have been exposed above the sea until late in terrestrial evolution.

欧帕林-霍尔丹猜想解决的是核酸聚合物和复合体的形成，而不是解离。然而，核酸是不寻常的，因为，在没有反离子(低盐)来中和对立磷酸基团的高电荷，核酸分解成单链。早期的潮汐，由近月驱动，可能产生快速的稀释周期(高潮，低盐)和浓缩周期(低潮时干燥下降，高盐) ，专门促进核酸的复制。这个理论受到了批评，理由是早期的潮汐可能没有那么快，尽管从现在的价值回归需要地球-月亮在2 Ga 左右并列，这是没有证据的，早期的潮汐可能大约每7小时一次。另一种批评是，只有2-3% 的地壳可能已经暴露在海洋之上，直到陆地演化的晚期。

A protocell is a self-organized, self-ordered, spherical collection of [[lipid]]s proposed as a stepping-stone to the origin of life.<ref name="Chen 2010">{{cite journal |first1=Irene A. |last1=Chen |first2=Peter |last2=Walde |title=From Self-Assembled Vesicles to Protocells |journal=Cold Spring Harbor Perspectives in Biology |date=July 2010 |volume=2 |issue=7 |page=a002170 |doi=10.1101/cshperspect.a002170 |pmc=2890201 |pmid=20519344}}</ref> A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation driving the evolution of life. Although a functional protocell has not yet been achieved in a laboratory setting, there are scientists who think the goal is well within reach.<ref name="Exploring">{{cite web |url=http://exploringorigins.org/protocells.html |title=Exploring Life's Origins: Protocells |website=Exploring Life's Origins: A Virtual Exhibit |publisher=National Science Foundation |location=Arlington County, VA |accessdate=2014-03-18 |url-status=live |archiveurl=https://web.archive.org/web/20140228083459/http://exploringorigins.org/protocells.html |archivedate=28 February 2014}}</ref><ref name="Chen 2006">{{cite journal |last=Chen |first=Irene A. |date=8 December 2006 |title=The Emergence of Cells During the Origin of Life |journal=Science |volume=314 |issue=5805 |pages=1558–1559 |doi=10.1126/science.1137541 |pmid=17158315 |doi-access=free }}</ref><ref name="Discover 2004">{{cite journal |last=Zimmer |first=Carl |authorlink=Carl Zimmer |date=26 June 2004 |title=What Came Before DNA? |url=http://discovermagazine.com/2004/jun/cover |journal=Discover |url-status=live |archiveurl=https://web.archive.org/web/20140319001351/http://discovermagazine.com/2004/jun/cover |archivedate=19 March 2014}}</ref>

The TCR (tidal chain reaction) theory has mechanistic advantages over thermal association/dissociation at deep-sea vents because TCR requires that chain assembly (template-driven polymerization) takes place during the dry-down phase, when precursors are most concentrated, whereas thermal cycling needs polymerization to take place during the cold phase, when the rate of chain assembly is lowest and precursors are likely to be more dilute.

潮汐链反应(TCR)理论比深海排气口热缔合/解离理论具有机械优势，因为 TCR 要求链组装(模板驱动聚合)发生在干燥阶段，这是前体最集中的阶段，而热循环需要在冷阶段进行聚合，这时链组装速率最低，前体可能更稀释。

Self-assembled [[Vesicle (biology and chemistry)|vesicles]] are essential components of primitive cells.<ref name="Chen 2010" /> The [[second law of thermodynamics]] requires that the universe move in a direction in which [[entropy]] increases, yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate [[Metabolism|life processes]] from non-living matter.<ref name="SciAm 2007">{{cite journal |last=Shapiro |first=Robert |authorlink=Robert Shapiro (chemist) |date=June 2007 |title=A Simpler Origin for Life |url=http://www.scientificamerican.com/article/a-simpler-origin-for-life/ |journal=Scientific American |volume=296 |issue=6 |pages=46–53 |doi=10.1038/scientificamerican0607-46 |pmid=17663224 |accessdate=2015-06-15 |bibcode=2007SciAm.296f..46S |url-status=live |archiveurl=https://web.archive.org/web/20150614000643/http://www.scientificamerican.com/article/a-simpler-origin-for-life/ |archivedate=14 June 2015}}</ref> Researchers Irene Chen and Szostak amongst others, suggest that simple physicochemical properties of elementary protocells can give rise to essential cellular behaviours, including primitive forms of differential reproduction competition and energy storage. Such cooperative interactions between the membrane and its encapsulated contents could greatly simplify the transition from simple replicating molecules to true cells.<ref name="Chen 2006" /> Furthermore, competition for membrane molecules would favour stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the [[phospholipid]]s of today.<ref name="Chen 2006" /> Such [[micro-encapsulation]] would allow for metabolism within the membrane, the exchange of small molecules but the prevention of passage of large substances across it.<ref>{{harvnb|Chang|2007}}</ref> The main advantages of encapsulation include the increased [[solubility]] of the contained cargo within the capsule and the storage of energy in the form of an [[electrochemical gradient]].

A 2012 study led by Mulkidjanian of the [[University of Osnabrück]], suggests that inland pools of condensed and cooled geothermal vapor have the ideal characteristics for the origin of life.<ref name="Switek 2012">{{cite news |last=Switek |first=Brian |date=13 February 2012 |title=Debate bubbles over the origin of life |work=Nature |location=London |publisher=Nature Publishing Group |doi=10.1038/nature.2012.10024}}</ref> Scientists confirmed in 2002 that by adding a [[montmorillonite]] clay to a solution of fatty acid micelles (lipid spheres), the clay sped up the rate of vesicles formation 100-fold.<ref name="Discover 2004" /> Furthermore, recent studies have found that the repeated actions of dehydration and rehydration trapped biomolecules like RNA inside the lipid protocells found within hot springs and providing the necessary preconditions for evolution by natural selection.<ref>{{Cite web|last=z3530495|date=2020-05-05|title='When chemistry became biology': looking for the origins of life in hot springs|url=https://newsroom.unsw.edu.au/news/science-tech/when-chemistry-became-biology-looking-origins-life-hot-springs|access-date=2020-10-12|website=UNSW Newsroom}}</ref>

Convection cells in fluid placed in a gravity field are selforganizing and enable thermal cycling of the suspended contents in the fluid such as protocells containing protoenzymes that work on thermal cycling.

置于重力场中的流体中的对流细胞是自组织的，使流体中悬浮的物质，例如含有热循环原始酶的原始细胞，能够进行热循环。

Emergence of chemiosmotic machinery Today's bioenergetic process of fermentation is carried out by either the aforementioned citric acid cycle or the Acetyl-CoA pathway, both of which have been connected to the primordial Iron–sulfur world.

化学渗透机制的出现今天的生物能量发酵过程是通过前面提到的三羧酸循环或乙酰辅酶 a 途径进行的，这两个途径都与原始的硫铁世界相连接。

=== Lipid vesicles formation in fresh water ===

[[Bruce Damer]] and [[David Deamer]] have come to the conclusion that [[cell membrane]]s cannot be formed in salty [[seawater]], and must therefore have originated in freshwater. Before the continents formed, the only dry land on Earth would be volcanic islands, where rainwater would form ponds where lipids could form the first stages towards cell membranes. These predecessors of true cells are assumed to have behaved more like a [[superorganism]] rather than individual structures, where the porous membranes would house molecules which would leak out and enter other protocells. Only when true cells had evolved would they gradually adapt to saltier environments and enter the ocean.<ref>{{cite journal |last1=Damer |first1=Bruce |last2=Deamer |first2=David |date=13 March 2015 |title=Coupled Phases and Combinatorial Selection in Fluctuating Hydrothermal Pools: A Scenario to Guide Experimental Approaches to the Origin of Cellular Life |journal=Life |volume=5 |issue=1 |pages=872–887 |doi=10.3390/life5010872 |pmc=4390883 |pmid=25780958}}</ref>

In a different approach, the thermosynthesis hypothesis considers the bioenergetic process of chemiosmosis, which plays an essential role in cellular respiration and photosynthesis, more basal than fermentation: the ATP synthase enzyme, which sustains chemiosmosis, is proposed as the currently extant enzyme most closely related to the first metabolic process.

在另一种方法中，热合成假说考虑了化学作用的生物能量过程，它在唿吸作用和光合作用中起着至关重要的作用，比发酵作用更基础: 维持化学作用的 ATP 合成酶，被认为是目前存在的与第一种代谢最密切相关的酶。

=== Vesicles consisting of mixtures of RNA-like biochemicals ===

First life needed an energy source to bring about the condensation reaction that yielded the peptide bonds of proteins and the phosphodiester bonds of RNA. In a generalization and thermal variation of the binding change mechanism of today's ATP synthase, the "first protein" would have bound substrates (peptides, phosphate, nucleosides, RNA 'monomers') and condensed them to a reaction product that remained bound until it was released after a temperature change by a thermal unfolding. The primordial first protein would therefore have strongly resembled the beta subunits of the ATP synthase alpha/beta subunits of today's F1 moiety in the FoF1 ATP synthase. Note however that today's enzymes function during isothermal conditions, whereas the hypothetical first protein worked on and during thermal cycling.

最初的生命需要一种能量来源来产生蛋白质的肽键和 RNA 的磷酸二酯键的缩合反应。概括地说，当今 ATP 合酶结合变化机制的热变化是，“第一个蛋白质”与底物(肽、磷酸、核苷、 RNA‘单体’)结合，并将它们凝结成反应产物，一直结合到温度变化后通过热展开释放。因此，在 f o f 1 ATP 合成酶中，原始第一蛋白与今天 f 1 ATP 合成酶 α/β 亚基的 β 亚基极为相似。然而，请注意，今天的酶在等温条件下起作用，而假设的第一个蛋白质在热循环中起作用。

Another protocell model is the [[Jeewanu]]. First synthesized in 1963 from simple minerals and basic organics while exposed to sunlight, it is still reported to have some metabolic capabilities, the presence of [[semipermeable membrane]], amino acids, phospholipids, [[carbohydrate]]s and RNA-like molecules.<ref name="Grote 2011">{{cite journal |last=Grote |first=Mathias |date=September 2011 |title=''Jeewanu'', or the 'particles of life' |url=http://www.ias.ac.in/jbiosci/grote_3677.pdf |journal=[[Journal of Biosciences]] |volume=36 |issue=4 |pages=563–570 |doi=10.1007/s12038-011-9087-0 |pmid=21857103 |s2cid=19551399 |accessdate=2015-06-15 |url-status=live |archiveurl=https://web.archive.org/web/20150924050938/http://www.ias.ac.in/jbiosci/grote_3677.pdf |archivedate=24 September 2015}}</ref><ref name="Gupta 2013">{{cite journal |last1=Gupta |first1=V.K. |last2=Rai |first2=R.K. |date=August 2013 |title=Histochemical localisation of RNA-like material in photochemically formed self-sustaining, abiogenic supramolecular assemblies 'Jeewanu' |url=https://www.academia.edu/9439398 |journal=International Research Journal of Science & Engineering |volume=1 |issue=1 |pages=1–4|accessdate=2015-06-15 |url-status=live |archiveurl=https://web.archive.org/web/20170628001930/http://www.academia.edu/9439398/Histochemical_Localisation_of_RNA_like_material_in_photochemically_formed_self-sustaining_abiogenic_supramolecular_assemblis_Jeewanu_ |archivedate=28 June 2017}}</ref> However, the nature and properties of the Jeewanu remains to be clarified.

The energy source under the thermosynthesis hypothesis was thermal cycling, the result of suspension of protocells in a convection current, as is plausible in a volcanic hot spring; the convection accounts for the self-organization and dissipative structure required in any origin of life model. The still ubiquitous role of thermal cycling in germination and cell division is considered a relic of primordial thermosynthesis.

热合成假说下的能量来源是热循环，原始细胞悬浮在对流流中的结果，这在火山温泉中似乎是合理的; 对流解释了任何生命起源模型所需的自我组织和耗散结构。热循环在发芽和细胞分裂中仍然普遍存在的作用被认为是原始热合成的遗迹。

Electrostatic interactions induced by short, positively charged, hydrophobic peptides containing 7 amino acids in length or fewer, can attach RNA to a vesicle membrane, the basic cell membrane.<ref>{{cite news |last=Welter |first=Kira |date=10 August 2015 |title=Peptide glue may have held first protocell components together |url=http://www.rsc.org/chemistryworld/2015/08/peptide-glue-rna-may-have-held-first-protocells-together |work=Chemistry World |type=News |location=London |publisher=Royal Society of Chemistry |accessdate= 2015-08-29 |url-status=live |archiveurl=https://web.archive.org/web/20150905234238/http://www.rsc.org/chemistryworld/2015/08/peptide-glue-rna-may-have-held-first-protocells-together |archivedate=5 September 2015}}</ref><ref>{{cite journal |last1=Kamat |first1=Neha P. |last2=Tobé |first2=Sylvia |last3=Hill |first3=Ian T. |last4=Szostak |first4=Jack W. |authorlink4=Jack W. Szostak |title=Electrostatic Localization of RNA to Protocell Membranes by Cationic Hydrophobic Peptides |date=29 July 2015 |journal=Angewandte Chemie International Edition |doi=10.1002/anie.201505742 |pmid=26223820 |pmc=4600236 |volume=54 |issue=40 |pages=11735–11739}}</ref>

By phosphorylating cell membrane lipids, this first protein gave a selective advantage to the lipid protocell that contained the protein. This protein also synthesized a library of many proteins, of which only a minute fraction had thermosynthesis capabilities. As proposed by Dyson, rather than a regular enzyme's mechanism, which decreases the free energy.

通过磷酸化细胞膜脂质，这种第一种蛋白质对含有这种蛋白质的脂质原细胞具有选择性优势。这种蛋白质还合成了许多蛋白质的文库，其中只有一小部分具有热合成能力。正如戴森提出的，而不是普通的酶的机制，减少自由能。

=== Metal-sulfide precipitates ===

William Martin and [[Michael Russell (scientist)|Michael Russell]] have suggested <blockquote>. . . . that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments,..."<ref name="Martin2003">{{cite journal |last1=Martin |first1=William |authorlink1=William F. Martin |last2=Russell |first2=Michael J. |date=29 January 2003 |title=On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells |journal=Philosophical Transactions of the Royal Society B |volume=358 |issue=1429 |pages=59–83; discussion 83–85 |doi=10.1098/rstb.2002.1183|pmid=12594918 |pmc=1693102}}</ref></blockquote>

The described first protein may be simple in the sense that is requires only a short sequence of conserved amino acid residues, a sequent sufficient for the appropriate catalytic cleft. In contrast, it has been claimed that the emergence of cyclic systems of protein catalysts such as required by fermentation is implausible because of the length of many required sequences.

所描述的第一个蛋白质可能是简单的，因为它只需要一个保守的氨基酸残基的短序列，这个序列对于适当的催化裂解是足够的。相比之下，有人声称，出现循环系统的蛋白质催化剂，如所需的发酵是难以置信的，因为许多所需序列的长度。

== Pertinent geological environments ==

It is possible that a different type of nucleic acid, such as peptide nucleic acid, threose nucleic acid or glycol nucleic acid, was the first to emerge as a self-reproducing molecule, only later replaced by RNA. Larralde et al., say that <blockquote>the generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity.</blockquote> and they conclude that their <blockquote>results suggest that the backbone of the first genetic material could not have contained ribose or other sugars because of their instability.</blockquote> The ester linkage of ribose and phosphoric acid in RNA is known to be prone to hydrolysis.

有可能是一种不同类型的核酸，如肽核酸、苏糖核酸或 GNA，最先以自我繁殖分子的形式出现，后来才被 RNA 所取代。Larralde 等人说，普遍接受的原生合成核糖，即台阶反应，产生大量的糖而没有任何选择性。他们得出结论，他们的结果表明，第一个遗传物质的骨干不可能含有核糖或其他糖，因为它们的不稳定性。已知 RNA 中核糖与磷酸的酯键易于水解。

===Darwin's little pond===

An early concept, that life originated from non-living matter in slow stages, appeared in [[Herbert Spencer]]'s 1864–1867 book ''Principles of Biology''. In 1879 [[William Turner Thiselton-Dyer]] referred to this in a paper "On spontaneous generation and evolution". On 1 February 1871 [[Charles Darwin]] wrote about these publications to [[Joseph Dalton Hooker|Joseph Hooker]], and set out his own speculation,<ref name="Darwin DCP-LETT-7471">{{cite web | title=Letter no. 7471, Charles Darwin to Joseph Dalton Hooker, 1 February (1871) | website=Darwin Correspondence Project | date= | url=https://www.darwinproject.ac.uk/letter/DCP-LETT-7471.xml | access-date=7 July 2020}}</ref><ref>{{cite web|url=https://www.nsf.gov/news/special_reports/darwin/textonly/polar_essay1.jsp|title=Origin and Evolution of Life on a Frozen Earth|last=Priscu|first=John C.|authorlink=John Charles Priscu|publisher=[[National Science Foundation]]|location=Arlington County, VA|archiveurl=https://web.archive.org/web/20131218070241/http://www.nsf.gov/news/special_reports/darwin/textonly/polar_essay1.jsp|archivedate=18 December 2013|url-status=live|accessdate=2014-03-01}}</ref> suggesting that the original spark of life may have begun in a <blockquote>warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, {{sic|hide=y|&c.}}, present, that a {{sic|hide=y|[[protein]]e}} compound was chemically formed ready to undergo still more complex changes.</blockquote> He went on to explain that <blockquote>at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.</blockquote>

Pyrimidine ribonucleosides and their respective nucleotides have been prebiotically synthesized by a sequence of reactions which by-pass the free sugars, and are assembled in a stepwise fashion by using nitrogenous or oxygenous chemistries. Sutherland has demonstrated high yielding routes to cytidine and uridine ribonucleotides built from small 2 and 3 carbon fragments such as glycolaldehyde, glyceraldehyde or glyceraldehyde-3-phosphate, cyanamide and cyanoacetylene. One of the steps in this sequence allows the isolation of enantiopure ribose aminooxazoline if the enantiomeric excess of glyceraldehyde is 60% or greater. This can be viewed as a prebiotic purification step, where the said compound spontaneously crystallized out from a mixture of the other pentose aminooxazolines. Ribose aminooxazoline can then react with cyanoacetylene in a mild and highly efficient manner to give the alpha cytidine ribonucleotide. Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry. In 2009 they showed that the same simple building blocks allow access, via phosphate controlled nucleobase elaboration, to 2',3'-cyclic pyrimidine nucleotides directly, which are known to be able to polymerize into RNA. This paper also highlights the possibility for the photo-sanitization of the pyrimidine-2',3'-cyclic phosphates.

嘧啶核苷及其核苷酸通过一系列绕过游离糖的反应进行预生物合成，并利用氮化或氧化化学分步组装。萨瑟兰已经证明了由乙醇醛、甘油醛或3- 磷酸甘油醛、氰胺和氰乙炔等2个和3个碳片段构建的胞苷和尿苷核苷的高产路线。如果甘油醛的对映体过量百分数大于或等于60% ，该序列中的一个步骤允许拆分对映体核糖氨基噁唑啉。这可以被看作是一个前生命净化步骤，即该化合物从其他戊糖氨基恶唑啉的混合物中自发结晶出来。核糖氨基噁唑啉可与氰乙炔温和高效地反应生成 α 胞苷核糖核苷。紫外光的光反向化允许在1’端反转，从而得到正确的 β 立体化学。2009年，他们展示了相同的简单构建模块，通过磷酸盐控制的核苷酸精化，可以直接进入2’ ，3’-环嘧啶核苷酸，这些核苷酸已知能够聚合成 RNA。本文还指出了对嘧啶 -2’ ，3’-环磷酸盐进行光消毒的可能性。

{{harvnb|Darwin|1887|p=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F1452.3&pageseq=30 18]}}:

While features of self-organization and self-replication are often considered the hallmark of living systems, there are many instances of abiotic molecules exhibiting such characteristics under proper conditions. Stan Palasek suggested based on a theoretical model that self-assembly of ribonucleic acid (RNA) molecules can occur spontaneously due to physical factors in hydrothermal vents. Virus self-assembly within host cells has implications for the study of the origin of life, as it lends further credence to the hypothesis that life could have started as self-assembling organic molecules.

虽然自我组织和自我复制的特征通常被认为是生命系统的标志，但在适当的条件下，有许多非生物分子表现出这些特征的实例。根据一个理论模型，Stan Palasek 认为在热液喷口的物理因素作用下，核糖核酸分子可以自发地自我组装。宿主细胞内的病毒自我组装对生命起源的研究具有重要意义，因为它进一步证实了生命可能是从自我组装的有机分子开始的这一假设。

It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, {{sic|&c.|hide=y}}, present, that a {{sic|[[protein]]e|hide=y}} compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.

— Darwin, 1 February 1871

Recent evidence for a "virus first" hypothesis, which may support theories of the RNA world, has been suggested. One of the difficulties for the study of the origins of viruses is their high rate of mutation; this is particularly the case in RNA retroviruses like HIV. A 2015 study compared protein fold structures across different branches of the tree of life, where researchers can reconstruct the evolutionary histories of the folds and of the organisms whose genomes code for those folds. They argue that protein folds are better markers of ancient events as their three-dimensional structures can be maintained even as the sequences that code for those begin to change. The data suggest that viruses originated from ancient cells that co-existed with the ancestors of modern cells. These ancient cells likely contained segmented RNA genomes.

“病毒优先”假说的最新证据，可能支持 RNA 世界的理论，已经被提出。病毒起源研究的困难之一是它们的高变异率，尤其是 RNA 逆转录病毒，如艾滋病毒。2015年的一项研究比较了生命之树不同分支的蛋白质折叠结构，研究人员可以重建折叠的进化历史，以及基因组为这些折叠编码的有机体的进化历史。他们认为蛋白质褶皱是古代事件更好的标记，因为它们的三维结构可以保持，即使编码这些事件的序列开始改变。这些数据表明，病毒起源于与现代细胞祖先共存的古老细胞。这些古老的细胞可能含有分段的 RNA 基因组。

More recent studies, in 2017, support the notion that life may have begun right after the Earth was formed as RNA molecules emerging from "warm little ponds".<ref name="IND-20171002">{{cite web |last=Johnston |first=Ian |title=Life first emerged in 'warm little ponds' almost as old as the Earth itself – Darwin's famous idea backed by new scientific study |url=https://www.independent.co.uk/news/science/origins-life-ponds-organisms-earth-age-study-a7978906.html |date=2 October 2017 |work=[[The Independent]] |accessdate=2 October 2017 |url-status=live |archiveurl=https://web.archive.org/web/20171003003027/http://www.independent.co.uk/news/science/origins-life-ponds-organisms-earth-age-study-a7978906.html |archivedate=3 October 2017}}</ref>

A computational model (2015) has shown that virus capsids may have originated in the RNA world and that they served as a means of horizontal transfer between replicator communities since these communities could not survive if the number of gene parasites increased, with certain genes being responsible for the formation of these structures and those that favored the survival of self-replicating communities. The displacement of these ancestral genes between cellular organisms could favor the appearance of new viruses during evolution. Viruses retain a replication module inherited from the prebiotic stage since it is absent in cells. Subsequent research has shown possible routes of synthesis; for example, formamide produces all four ribonucleotides and other biological molecules when warmed in the presence of various terrestrial minerals.

2015年的《计算模型表明，病毒衣壳可能起源于 RNA 世界，它们是复制因子群落之间水平转移的一种手段，因为如果基因寄生虫的数量增加，这些群落就无法生存，某些基因负责这些结构的形成，而那些基因有利于自我复制群落的生存。在进化过程中，这些原始基因在细胞生物体之间的移位可能有利于新病毒的出现。病毒保留了从前生命阶段遗传下来的复制模块，因为它在细胞中是不存在的。随后的研究显示了可能的合成路线; 例如，甲酰胺在各种陆地矿物存在的情况下加热时会产生所有四种核糖核苷酸和其他生物分子。

===Volcanic hot springs and hydrothermal vents, shallow or deep===

Relatively short RNA molecules have been synthesized, capable of replication. Such replicase RNA, which functions as both code and catalyst provides its own template upon which copying can occur. Szostak has shown that certain catalytic RNAs can join smaller RNA sequences together, creating the potential for self-replication. If these conditions were present, Darwinian natural selection would favour the proliferation of such autocatalytic sets, to which further functionalities could be added. Such autocatalytic systems of RNA capable of self-sustained replication have been identified. The RNA replication systems, which include two ribozymes that catalyze each other's synthesis, showed a doubling time of the product of about one hour, and were subject to natural selection under the conditions that existed in the experiment.

相对较短的 RNA 分子已被合成，能够复制。这种作为编码和催化剂的复制酶 RNA 提供了自己的模板，可以进行复制。已经证明，某些催化 RNA 可以连接更小的 RNA 序列，创造出自我复制的潜力。如果存在这些条件，达尔文的自然选择理论将有利于这种自催化集的扩散，而这种自催化集还可以增加更多的功能。这种能够自我维持复制的 RNA 的自我催化系统已经被确定。复制系统包括两个核酶，它们相互催化对方的合成，表明产物的倍增时间约为一小时，并在实验条件下受自然选择的影响。

{{for|branching of Bacteria phyla|Bacterial phyla}}

Martin Brazier has shown that early micro-fossils came from a hot world of gases such as [[methane]], [[ammonia]], [[carbon dioxide]] and [[hydrogen sulphide]], which are toxic to much current life.<ref>

Depending on the definition, life started when RNA chains began to self-replicate, initiating the three mechanisms of Darwinian selection: heritability, variation of type, and differential reproductive output. The fitness of an RNA replicator (its per capita rate of increase) would likely be a function of its intrinsic adaptive capacities, determined by its nucleotide sequence, and the availability of resources. The three primary adaptive capacities may have been: (1) replication with moderate fidelity, giving rise to both heritability while allowing variation of type, (2) resistance to decay, and (3) acquisition of process resources. Following on from chemical evolution came the initiation of biological evolution, which led to the first cells. However, some researchers work in this field, notably Steen Rasmussen and Szostak.

根据这个定义，生命起源于 RNA 链开始自我复制，启动了达尔文选择的三种机制: 遗传力、类型变异和差异繁殖输出。RNA 复制因子的适合度(人均增长率)很可能是其内在适应能力的函数，由其核苷酸序列和资源的可用性决定。这三种主要的适应能力可能是: (1)中保真度复制，在允许类型变异的同时提高遗传力，(2)抗腐性，(3)获得工艺资源。随着化学进化而来的是生物进化的开始，进而产生了第一批细胞。然而，一些研究人员在这个领域工作，特别是斯蒂恩 · 拉斯穆森和绍斯塔克。

M.D> Brasier (2012), "Secret Chambers: The Inside Story of Cells and Complex Life" (Oxford Uni Press), p.298</ref> Another analysis of the conventional threefold tree of life shows thermophilic and hyperthermophilic [[bacteria]] and [[archaea]] are closest to the root, suggesting that life may have evolved in a hot environment.<ref>Ward, Peter & Kirschvink, Joe, op cit, p. 42</ref>

Others have argued that a "top-down approach" is more feasible, starting with simple forms of current life. Spiegelman took advantage of natural selection to synthesize the Spiegelman Monster, which had a genome with just 218 nucleotide bases, having deconstructively evolved from a 4500-base bacterial RNA. Eigen built on Spiegelman's work and produced a similar system further degraded to just 48 or 54 nucleotides—the minimum required for the binding of the replication enzyme. Craig Venter and others at J. Craig Venter Institute engineered existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life are reached.

另一些人则认为，“自上而下的方法”更为可行，从简单的当前生活形式开始。Spiegelman 利用自然选择合成了 Spiegelman Monster，它的基因组只有218个核苷酸碱基，从一个4500碱基的细菌 RNA 解构进化而来。Eigen 建立在 Spiegelman 的工作基础上，产生了一个类似的系统，进一步降解到只有48或54个核苷酸——这是结合复制酶所需的最小值。克莱格·凡特研究所的 Craig Venter 和其他研究人员用越来越少的基因改造了现有的原核细胞，试图辨别在哪一点达到了生命的最低需求。

===Deep sea hydrothermal vents===

[[File:Blacksmoker in Atlantic Ocean.jpg|thumb|upright|Deep-sea hydrothermal vent or [[black smoker]]]]

In October 2018, researchers at McMaster University announced the development of a new technology, called a Planet Simulator, to help study the origin of life on planet Earth and beyond. It consists of a sophisticated climate chamber to study how the building blocks of life were assembled and how these prebiotic molecules transitioned into self-replicating RNA molecules.

2018年10月，麦马士达大学的研究人员宣布开发一项新技术，称为行星模拟器，以帮助研究地球及其他星球上生命的起源。它由一个复杂的气候室组成，用来研究生命的组成部分是如何组装的，以及这些前生命体分子是如何转化成自我复制的 RNA 分子的。

The deep sea vent, or alkaline [[hydrothermal vent]], theory posits that life may have begun at submarine hydrothermal vents,<ref name=":1">{{Cite journal|author1=Colín-García, M.|author2=A. Heredia|author3=G. Cordero|author4=A. Camprubí|author5=A. Negrón-Mendoza|author6=F. Ortega-Gutiérrez|author7=H. Berald|author8=S. Ramos-Bernal|year=2016|title=Hydrothermal vents and prebiotic chemistry: a review|url=http://boletinsgm.igeolcu.unam.mx/bsgm/index.php/component/content/article/309-sitio/articulos/cuarta-epoca/6803/1620-6803-13-colin|journal=Boletín de la Sociedad Geológica Mexicana|volume=68|issue=3|pages=599–620|url-status=live|archiveurl=https://web.archive.org/web/20170818175803/http://boletinsgm.igeolcu.unam.mx/bsgm/index.php/component/content/article/309-sitio/articulos/cuarta-epoca/6803/1620-6803-13-colin|archivedate=18 August 2017|doi=10.18268/BSGM2016v68n3a13|doi-access=free}}</ref><ref name="hydrothermal vents NASA 2014">{{cite web|url=https://astrobiology.nasa.gov/articles/2014/6/24/hydrothermal-vents-could-explain-chemical-precursors-to-life/ |title=Hydrothermal Vents Could Explain Chemical Precursors to Life |last=Schirber |first=Michael |date=24 June 2014 |website=NASA Astrobiology: Life in the Universe |publisher=NASA |accessdate=2015-06-19 |url-status=dead |archiveurl=https://web.archive.org/web/20141129051724/http://astrobiology.nasa.gov/articles/2014/6/24/hydrothermal-vents-could-explain-chemical-precursors-to-life/ |archivedate=29 November 2014}}</ref> Martin and Russell have suggested <blockquote>that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments,...<ref name="Martin2003" /></blockquote> These form where hydrogen-rich fluids emerge from below the sea floor, as a result of [[Serpentinite|serpentinization]] of ultra-[[mafic]] [[olivine]] with seawater and a pH interface with carbon dioxide-rich ocean water. The vents form a sustained chemical energy source derived from redox reactions, in which electron donors (molecular hydrogen) react with electron acceptors (carbon dioxide); see [[Iron–sulfur world theory]]. These are highly [[exothermic reaction]]s.<ref name=":1" />{{efn|The reactions are: 

'''Reaction 1''': Fayalite + water → magnetite + aqueous silica + hydrogen

:3Fe2SiO4 + 2H2O → 2Fe3O4 + 3SiO2 + 2H2

'''Reaction 2''': Forsterite + aqueous silica → serpentine

:3Mg2SiO4 + SiO2 + 4H2O → 2Mg3Si2O5(OH)4

'''Reaction 3''': Forsterite + water → serpentine + brucite

:2Mg2SiO4 + 3H2O → Mg3Si2O5(OH)4 + Mg(OH)2

Reaction 3 describes the hydration of olivine with water only to yield [[Serpentine group|serpentine]] and Mg(OH)2 ([[brucite]]). Serpentine is stable at high pH in the presence of brucite like calcium silicate hydrate, ([[calcium silicate hydrate|C-S-H]]) phases formed along with [[portlandite]] (Ca(OH)2) in hardened [[Portland cement]] paste after the hydration of [[belite]] (Ca2SiO4), the artificial calcium equivalent of forsterite.

Analogy of reaction 3 with belite hydration in ordinary Portland cement: ''Belite + water → C-S-H phase + portlandite''

:2 Ca2SiO4 + 4 H2O → 3 CaO · 2 SiO2 · 3 H2O + Ca(OH)2}}

Russell demonstrated that alkaline vents created an abiogenic [[Proton electromotive force|proton motive force]] (PMF) [[Chemiosmosis|chemiosmotic]] gradient,<ref name="Martin2003" /> in which conditions are ideal for an abiogenic hatchery for life. Their microscopic compartments "provide a natural means of concentrating organic molecules," composed of iron-sulfur minerals such as [[mackinawite]], endowed these mineral cells with the catalytic properties envisaged by [[Günter Wächtershäuser]].<ref name="Lane 2009" /> This movement of ions across the membrane depends on a combination of two factors:

# [[Diffusion]] force caused by concentration gradient—all particles including ions tend to diffuse from higher concentration to lower.

# Electrostatic force caused by electrical potential gradient—[[cations]] like [[proton]]s H+ tend to diffuse down the electrical potential, [[anions]] in the opposite direction.

These two gradients taken together can be expressed as an [[electrochemical gradient]], providing energy for abiogenic synthesis. The proton motive force can be described as the measure of the potential energy stored as a combination of proton and voltage gradients across a membrane (differences in proton concentration and electrical potential).



Szostak suggested that geothermal activity provides greater opportunities for the origination of life in open lakes where there is a buildup of minerals. In 2010, based on spectral analysis of sea and hot mineral water, Ignat Ignatov and Oleg Mosin demonstrated that life may have predominantly originated in hot mineral water. The hot mineral water that contains [[bicarbonate]] and [[calcium]] ions has the most optimal range.<ref>{{cite journal |last1=Ignatov |first1=Ignat |last2=Mosin |first2=Oleg V. |year=2013 |title=Possible Processes for Origin of Life and Living Matter with modeling of Physiological Processes of Bacterium ''Bacillus Subtilis'' in Heavy Water as Model System |journal=Journal of Natural Sciences Research |volume=3 |issue=9 |pages=65–76}}</ref> This case is similar to the origin of life in hydrothermal vents, but with bicarbonate and calcium ions in hot water. This water has a pH of 9–11 and is possible to have the reactions in seawater. According to [[Melvin Calvin]], certain reactions of condensation-dehydration of amino acids and nucleotides in individual blocks of peptides and nucleic acids can take place in the primary hydrosphere with pH 9–11 at a later evolutionary stage.<ref>{{harvnb|Calvin|1969}}</ref> Some of these compounds like [[Hydrogen cyanide|hydrocyanic acid]] (HCN) have been proven in the experiments of Miller. This is the environment in which the [[stromatolite]]s have been created. David Ward of [[Montana State University]] described the formation of stromatolites in hot mineral water at the [[Yellowstone National Park]]. Stromatolites survive in hot mineral water and in proximity to areas with volcanic activity.<ref>{{cite journal |last=Schirber |first=Michael |date=1 March 2010 |title=First Fossil-Makers in Hot Water |url=http://www.astrobio.net/news-exclusive/first-fossil-makers-in-hot-water/ |journal=[[Astrobiology Magazine]] |accessdate=2015-06-19 |url-status=live |archiveurl=https://web.archive.org/web/20150714085640/http://www.astrobio.net/news-exclusive/first-fossil-makers-in-hot-water/ |archivedate=14 July 2015}}</ref> Processes have evolved in the sea near geysers of hot mineral water.

In 2011, Tadashi Sugawara from the [[University of Tokyo]] created a protocell in hot water.<ref>{{cite journal |last1=Kurihara |first1=Kensuke |last2=Tamura |first2=Mieko |last3=Shohda |first3=Koh-ichiroh |last4=Toyota |first4=Taro |last5=Suzuki |first5=Kentaro |last6=Sugawara |first6=Tadashi |display-authors=3 |date=October 2011 |title=Self-Reproduction of supramolecular giant vesicles combined with the amplification of encapsulated DNA |journal=Nature Chemistry |volume=3 |issue=10 |pages=775–781 |bibcode=2011NatCh...3..775K |doi=10.1038/nchem.1127|pmid=21941249}}</ref>

Experimental research and computer modelling suggest that the surfaces of mineral particles inside hydrothermal vents have catalytic properties similar to those of enzymes and are able to create simple organic molecules, such as [[methanol]] (CH3OH) and [[Formic acid|formic]], [[Acetic acid|acetic]] and [[Pyruvic acid|pyruvic]] acid out of the dissolved CO2 in the water.<ref name="organics">{{cite press release |last=Usher |first=Oli |date=27 April 2015 |title=Chemistry of seabed's hot vents could explain emergence of life |url=https://www.ucl.ac.uk/silva/mathematical-physical-sciences/maps-news-publication/maps1526 |publisher=[[University College London]] |accessdate=2015-06-19 |archive-url=https://web.archive.org/web/20150620012231/https://www.ucl.ac.uk/silva/mathematical-physical-sciences/maps-news-publication/maps1526 |archive-date=20 June 2015 |url-status=dead}}</ref><ref>{{cite journal |last1=Roldan |first1=Alberto |last2=Hollingsworth |first2=Nathan |last3=Roffey |first3=Anna |last4=Islam |first4=Husn-Ubayda |last5=Goodall |first5=Josephine B. M. |last6=Catlow |first6=C. Richard A. |authorlink6=Richard Catlow |last7=Darr |first7=Jawwad A. |last8=Bras |first8=Wim |last9=Sankar |first9=Gopinathan |last10=Holt |first10=Katherine B. |last11=Hogarth |first11=Graeme |last12=de Leeuw |first12=Nora Henriette |display-authors=4 |date=May 2015 |title=Bio-inspired CO2 conversion by iron sulfide catalysts under sustainable conditions |url=http://pubs.rsc.org/en/content/articlepdf/2015/cc/c5cc02078f|journal=Chemical Communications |volume=51 |issue=35 |pages=7501–7504 |doi=10.1039/C5CC02078F |pmid=25835242 |accessdate=2015-06-19 |url-status=live |archiveurl=https://web.archive.org/web/20150620003943/http://pubs.rsc.org/en/content/articlepdf/2015/cc/c5cc02078f |archivedate=20 June 2015|doi-access=free }}</ref>

Footnotes

脚注

The research reported above by Martin in 2016 supports the thesis that life arose at hydrothermal vents,<ref>{{cite journal | last1 = Baross | first1 = J.A. | last2 = Hoffman | first2 = S.E. | year = 1985 | title = Submarine hydrothermal vents and associated gradient environments as sites for the origin and evolution of life | journal = Origins LifeEvol. B | volume = 15 | issue = 4 | pages = 327–345 | doi=10.1007/bf01808177| bibcode = 1985OrLi...15..327B | s2cid = 4613918 }}</ref><ref>{{cite journal | last1 = Russell | first1 = M.J. | last2 = Hall | first2 = A.J. | year = 1997 | title = The emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and pH front | journal = Journal of the Geological Society| volume = 154 | issue = 3 | pages = 377–402 | doi=10.1144/gsjgs.154.3.0377| pmid = 11541234 | bibcode = 1997JGSoc.154..377R | s2cid = 24792282 }}</ref> that spontaneous chemistry in the Earth's crust driven by rock–water interactions at disequilibrium thermodynamically underpinned life's origin<ref>{{cite journal | last1 = Amend | first1 = J.P. | last2 = LaRowe | first2 = D.E. | last3 = McCollom | first3 = T.M. | last4 = Shock | first4 = E.L. | year = 2013 | title = The energetics of organic synthesis inside and outside the cell | journal = Phil. Trans. R. Soc. Lond. B | volume = 368 | issue = 1622 | page = 20120255 | doi=10.1098/rstb.2012.0255| pmid = 23754809 | pmc = 3685458 }}</ref><ref>{{cite journal | last1 = Shock | first1 = E.L. | last2 = Boyd | first2 = E.S. | year = 2015 | title = Geomicrobiology and microbial geochemistry:principles of geobiochemistry | journal = Elements | volume = 11 | pages = 389–394 | doi = 10.2113/gselements.11.6.395 }}</ref> and that the founding lineages of the archaea and bacteria were H2-dependent autotrophs that used CO2 as their terminal acceptor in energy metabolism.<ref>{{cite journal | last1 = Martin | first1 = W. | last2 = Russell | first2 = M.J. | year = 2007 | title = On the origin of biochemistry at an alkaline hydrothermal vent | journal = Phil. Trans. R. Soc. Lond. B | volume = 362 | issue = 1486 | pages = 1887–1925 | doi = 10.1098/rstb.2006.1881 | pmid = 17255002 | pmc = 2442388 }}</ref> Martin suggests, based upon this evidence that [[LUCA]] "may have depended heavily on the geothermal energy of the vent to survive".<ref>Nature, Vol 535, 28 July 2016. p.468</ref>

=== Fluctuating hydrothermal pools on volcanic islands or proto-continents ===

Citations

引文

Mulkidjanian and co-authors think that the marine environments did not provide the ionic balance and composition universally found in cells, as well as of ions required by essential proteins and ribozymes found in virtually all living organisms, especially with respect to K+/Na+ ratio, Mn2+, Zn2+ and phosphate concentrations. The only known environments that mimic the needed conditions on Earth are found in terrestrial hydrothermal pools fed by steam vents.<ref name=":1" /> Additionally, mineral deposits in these environments under an anoxic atmosphere would have suitable pH (as opposed to current pools in an oxygenated atmosphere), contain precipitates of sulfide minerals that block harmful UV radiation, have wetting/drying cycles that concentrate substrate solutions to concentrations amenable to spontaneous formation of polymers of nucleic acids, polyesters<ref>{{cite journal |last1=Chandru |first1=Kuhan |last2=Guttenberg |first2=Nicholas |last3=Giri |first3=Chaitanya |last4=Hongo |first4=Yayoi |last5=Butch |first5=Christopher |last6=Mamajanov |first6=Irena |last7=Cleaves |first7=H. James |title=Simple prebiotic synthesis of high diversity dynamic combinatorial polyester libraries |journal=Communications Chemistry |date=31 May 2018 |volume=1 |issue=1 |doi=10.1038/s42004-018-0031-1 |doi-access=free }}</ref> and depsipeptides,<ref>{{cite journal |last1=Forsythe |first1=Jay G |last2=Yu |first2=Sheng-Sheng |last3=Mamajanov |first3=Irena |last4=Grover |first4=Martha A |last5=Krishnamurthy |first5=Ramanarayanan |last6=Fernández |first6=Facundo M |last7=Hud |first7=Nicholas V |title=Ester-Mediated Amide Bond Formation Driven by Wet–Dry Cycles: A Possible Path to Polypeptides on the Prebiotic Earth |journal=Angewandte Chemie (International ed. In English) |date=17 August 2015 |volume=54 |issue=34 |pages=9871–9875 |doi=10.1002/anie.201503792 |pmid=26201989 |pmc=4678426 }}</ref> both by chemical reactions in the hydrothermal environment, as well as by exposure to [[UV light]] during transport from vents to adjacent pools. Their hypothesized pre-biotic environments are similar to the deep-oceanic vent environments most commonly hypothesized, but add additional components that help explain peculiarities found in reconstructions of the [[Last Universal Common Ancestor]] (LUCA) of all living organisms.<ref>{{cite journal |last1=Mulkidjanian |first1=Armid |last2=Bychkov |first2=Andrew |last3=Dibrova |first3=Daria |last4=Galperin |first4=Michael |last5=Koonin |first5=Eugene |date=3 April 2012 |title=Origin of first cells at terrestrial, anoxic geothermal fields |journal=PNAS |volume=109 |issue=14 |pages=E821–E830 |doi=10.1073/pnas.1117774109 |pmid=22331915 |pmc=3325685|bibcode=2012PNAS..109E.821M }}</ref>

Colín-García ''et al.'' (2016) discuss the advantages and disadvantages of hydrothermal vents as primitive environments.<ref name=":1"/> They mention the exergonic reactions in such systems could have been a source of free energy that promoted chemical reactions, additional to their high mineralogical diversity which implies the induction of important chemical gradients, thus favoring the interaction between electron donors and acceptors. Colín-García ''et al.'' (2016) also summarize a set of experiments proposed to test the role of hydrothermal vents in prebiotic synthesis.<ref name=":1"/>

===Volcanic ash in the ocean===

[[Geoffrey W. Hoffmann]] has argued that a complex nucleation event as the origin of life involving both polypeptides and nucleic acid is compatible with the time and space available in the primitive oceans of Earth<ref>{{cite biorxiv|last1=Hoffmann|first1=Geoffrey William|title=A network theory of the origin of life|date=24 December 2016|biorxiv=10.1101/096701}}</ref> Hoffmann suggests that volcanic ash may provide the many random shapes needed in the postulated complex nucleation event. This aspect of the theory can be tested experimentally.

=== Gold's deep-hot biosphere ===

In the 1970s, [[Thomas Gold]] proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface. It is claimed that the discovery of microbial life below the surface of another body in our Solar System would lend significant credence to this theory. Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. Gold's theory is that the flow of such food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes (away from sedimentary carbon compounds) is that the organisms [[Microbial metabolism#Hydrogen oxidation|subsist on hydrogen]] released by an interaction between water and (reduced) iron compounds in rocks.

=== Radioactive beach hypothesis ===

Zachary Adam claims that tidal processes that occurred during a time when the Moon was much closer may have concentrated grains of [[uranium]] and other radioactive elements at the high-water mark on primordial beaches, where they may have been responsible for generating life's building blocks.<ref>{{cite journal |last=Dartnell |first=Lewis |date=12 January 2008 |title=Did life begin on a radioactive beach? |url=https://www.newscientist.com/article/mg19726384.000-did-life-begin-on-a-radioactive-beach.html |journal=New Scientist |issue=2638 |page=8 |accessdate=2015-06-26 |url-status=live |archiveurl=https://web.archive.org/web/20150627101858/http://www.newscientist.com/article/mg19726384.000-did-life-begin-on-a-radioactive-beach.html |archivedate=27 June 2015}}</ref> According to computer models,<ref>{{cite journal |last=Adam |first=Zachary |year=2007 |title=Actinides and Life's Origins |journal=Astrobiology |volume=7 |issue=6 |pages=852–872 |bibcode=2007AsBio...7..852A |doi=10.1089/ast.2006.0066|pmid=18163867}}</ref> a deposit of such radioactive materials could show the same [[Natural nuclear fission reactor|self-sustaining nuclear reaction]] as that found in the [[Oklo]] uranium ore seam in [[Gabon]]. Such radioactive beach sand might have provided sufficient energy to generate organic molecules, such as amino acids and sugars from [[acetonitrile]] in water. Radioactive [[monazite]] material also has released soluble phosphate into the regions between sand-grains, making it biologically "accessible." Thus amino acids, sugars, and soluble phosphates might have been produced simultaneously, according to Adam. Radioactive [[actinide]]s, left behind in some concentration by the reaction, might have formed part of [[Organometallic chemistry|organometallic complexes]]. These complexes could have been important early catalysts to living processes.

John Parnell has suggested that such a process could provide part of the "crucible of life" in the early stages of any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface. As the early Earth is thought to have had many smaller plates, it might have provided a suitable environment for such processes.<ref>{{cite journal |last=Parnell |first=John |date=December 2004 |title=Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth |journal=Origins of Life and Evolution of Biospheres |volume=34 |issue=6 |pages=533–547 |bibcode=2004OLEB...34..533P |doi=10.1023/B:ORIG.0000043132.23966.a1 |pmid=15570707|citeseerx=10.1.1.456.8955 |s2cid=6067448 }}</ref>

== Origin of metabolism: physiology ==

Different forms of life with variable origin processes may have appeared quasi-simultaneously in the early [[history of Earth]].<ref>{{cite journal |last=Davies |first=Paul |authorlink=Paul Davies |date=December 2007 |title=Are Aliens Among Us? |url=http://www.zo.utexas.edu/courses/kalthoff/bio301c/readings/07Davies.pdf |journal=Scientific American |volume=297 |issue=6 |pages=62–69 |doi=10.1038/scientificamerican1207-62 |accessdate=2015-07-16 |quote=...if life does emerge readily under terrestrial conditions, then perhaps it formed many times on our home planet. To pursue this possibility, deserts, lakes and other extreme or isolated environments have been searched for evidence of "alien" life-forms—organisms that would differ fundamentally from known organisms because they arose independently. |bibcode=2007SciAm.297f..62D |url-status=live |archiveurl=https://web.archive.org/web/20160304185832/http://www.zo.utexas.edu/courses/kalthoff/bio301c/readings/07Davies.pdf |archivedate=4 March 2016}}</ref> The other forms may be extinct (having left distinctive fossils through their different biochemistry—e.g., [[hypothetical types of biochemistry]]). It has been proposed that:

<blockquote>The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other [[dicarboxylic acid]]s. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoiesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore, the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.<ref>{{cite journal |last=Hartman |first=Hyman |date=1998 |title=Photosynthesis and the Origin of Life |journal=Origins of Life and Evolution of Biospheres |volume=28 |issue=4–6 |pages=515–521 |bibcode=1998OLEB...28..515H |doi=10.1023/A:1006548904157 |pmid=11536891|s2cid=2464 }}</ref></blockquote>

Metabolism-like reactions could have occurred naturally in early oceans, before the first organisms evolved.<ref name="Ralser 2014" /><ref name="Metabolism 2014">{{cite press release |last=Senthilingam |first=Meera |date=25 April 2014 |title=Metabolism May Have Started in Early Oceans Before the Origin of Life |url=http://www.eurekalert.org/pub_releases/2014-04/wt-mmh042314.php |publisher=[[Wellcome Trust]] |agency=[[American Association for the Advancement of Science|EurekAlert!]] |accessdate=2015-06-16 |url-status=live |archiveurl=https://web.archive.org/web/20150617102656/http://www.eurekalert.org/pub_releases/2014-04/wt-mmh042314.php |archivedate=17 June 2015}}</ref> Metabolism may predate the origin of life, which may have evolved from the chemical conditions in the earliest oceans. Reconstructions in laboratories show that some of these reactions can produce RNA, and some others resemble two essential reaction cascades of metabolism: [[glycolysis]] and the [[pentose phosphate pathway]], that provide essential precursors for nucleic acids, amino acids and lipids.<ref name="Metabolism 2014" />

=== Clay hypothesis ===

[[Montmorillonite]], an abundant [[clay]], is a catalyst for the polymerization of RNA and for the formation of membranes from lipids.<ref>{{cite press release |last=Perry |first=Caroline |date=7 February 2011 |title=Clay-armored bubbles may have formed first protocells |url=http://www.eurekalert.org/pub_releases/2011-02/hu-cbm020411.php |location=Cambridge, MA |publisher=[[Harvard University]] |agency=EurekAlert! |accessdate=2015-06-20 |url-status=live |archiveurl=https://web.archive.org/web/20150714101638/http://www.eurekalert.org/pub_releases/2011-02/hu-cbm020411.php |archivedate=14 July 2015}}</ref> A model for the origin of life using clay was forwarded by Alexander Cairns-Smith in 1985 and explored as a plausible mechanism by several scientists.<ref>{{harvnb|Dawkins|1996|pp=148–161}}</ref> The clay hypothesis postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in solution.

At the [[Rensselaer Polytechnic Institute]], James Ferris' studies have also confirmed that montmorillonite clay minerals catalyze the formation of RNA in aqueous solution, by joining nucleotides to form longer chains.<ref>{{cite journal |author1=Wenhua Huang |last2=Ferris |first2=James P. |date=12 July 2006 |title=One-Step, Regioselective Synthesis of up to 50-mers of RNA Oligomers by Montmorillonite Catalysis |journal=Journal of the American Chemical Society |volume=128 |issue=27 |pages=8914–8919 |doi=10.1021/ja061782k |pmid=16819887}}</ref>

In 2007, Bart Kahr from the [[University of Washington]] and colleagues reported their experiments that tested the idea that crystals can act as a source of transferable information, using crystals of [[potassium hydrogen phthalate]]. "Mother" crystals with imperfections were cleaved and used as seeds to grow "daughter" crystals from solution. They then examined the distribution of imperfections in the new crystals and found that the imperfections in the mother crystals were reproduced in the daughters, but the daughter crystals also had many additional imperfections. For gene-like behavior to be observed, the quantity of inheritance of these imperfections should have exceeded that of the mutations in the successive generations, but it did not. Thus Kahr concluded that the crystals "were not faithful enough to store and transfer information from one generation to the next."<ref>{{cite journal |last=Moore |first=Caroline |date=16 July 2007 |title=Crystals as genes? |url=http://www.rsc.org/Publishing/ChemScience/Volume/2007/08/Crystals_as_genes.asp |journal=Highlights in Chemical Science |accessdate=2015-06-21 |url-status=live |archiveurl=https://web.archive.org/web/20150714094855/http://www.rsc.org/Publishing/ChemScience/Volume/2007/08/Crystals_as_genes.asp |archivedate=14 July 2015}}

* {{cite journal |last1=Bullard |first1=Theresa |last2=Freudenthal |first2=John |last3=Avagyan |first3=Serine |last4=Kahr |first4=Bart |display-authors=3 |year=2007 |title=Test of Cairns-Smith's 'crystals-as-genes' hypothesis |journal=[[Faraday Discussions]] |volume=136 |pages=231–245 |bibcode=2007FaDi..136..231B |doi=10.1039/b616612c |pmid=17955812 }}</ref>

=== Iron–sulfur world ===

{{Main|Iron–sulfur world theory}}

In the 1980s, Günter Wächtershäuser, encouraged and supported by [[Karl R. Popper|Karl Popper]],<ref>{{cite journal |last=Yue-Ching Ho |first=Eugene |date=July–September 1990 |title=Evolutionary Epistemology and Sir Karl Popper's Latest Intellectual Interest: A First-Hand Report |url=http://www.tkpw.net/hk-ies/n15/ |journal=Intellectus |volume=15 |pages=1–3 |oclc=26878740 |accessdate=2012-08-13 |url-status=live |archiveurl=https://web.archive.org/web/20120311074143/http://www.tkpw.net/hk-ies/n15/ |archivedate=11 March 2012}}</ref><ref>{{cite news |last=Wade |first=Nicholas |date=22 April 1997 |title=Amateur Shakes Up Ideas on Recipe for Life |url=https://www.nytimes.com/1997/04/22/science/amateur-shakes-up-ideas-on-recipe-for-life.html?src=pm&pagewanted=2&pagewanted=all |newspaper=The New York Times |location=New York |accessdate=2015-06-16 |url-status=live |archiveurl=https://web.archive.org/web/20150617122450/http://www.nytimes.com/1997/04/22/science/amateur-shakes-up-ideas-on-recipe-for-life.html?src=pm&pagewanted=2&pagewanted=all |archivedate=17 June 2015}}</ref><ref>{{cite journal |last=Popper |first=Karl R. |authorlink=Karl Popper |date=29 March 1990 |title=Pyrite and the origin of life |journal=Nature |volume=344 |issue=6265 |page=387 |bibcode=1990Natur.344..387P |doi=10.1038/344387a0 |s2cid=4322774 }}</ref> postulated his iron–sulfur world, a theory of the evolution of pre-biotic chemical pathways as the starting point in the evolution of life. It systematically traces today's biochemistry to primordial reactions which provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds.

In contrast to the classical Miller experiments, which depend on external sources of energy (simulated lightning, ultraviolet [[irradiation]]), "Wächtershäuser systems" come with a built-in source of energy: [[sulfide]]s of iron (iron [[pyrite]]) and other minerals. The energy released from [[redox]] reactions of these metal sulfides is available for the synthesis of organic molecules, and such systems may have evolved into autocatalytic sets constituting self-replicating, metabolically active entities predating the life forms known today.<ref name="Ralser 2014" /><ref name="Metabolism 2014" /> Experiments with such sulfides in an aqueous environment at 100 °C produced a relatively small yield of [[dipeptide]]s (0.4% to 12.4%) and a smaller yield of [[tripeptide]]s (0.10%) although under the same conditions, dipeptides were quickly broken down.<ref>{{cite journal |last1=Huber |first1=Claudia |last2=Wächtershäuser |first2=Günter |authorlink2=Günter Wächtershäuser |date=31 July 1998 |title=Peptides by Activation of Amino Acids with CO on (Ni,Fe)S Surfaces: Implications for the Origin of Life |journal=Science |volume=281 |issue=5377 |pages=670–672 |bibcode=1998Sci...281..670H |doi=10.1126/science.281.5377.670 |pmid=9685253}}</ref>

Several models reject the self-replication of a "naked-gene", postulating instead the emergence of a primitive metabolism providing a safe environment for the later emergence of RNA replication. The centrality of the [[Citric acid cycle|Krebs cycle]] (citric acid cycle) to energy production in aerobic organisms, and in drawing in carbon dioxide and hydrogen ions in biosynthesis of complex organic chemicals, suggests that it was one of the first parts of the metabolism to evolve.<ref name="Lane 2009">{{harvnb|Lane|2009}}</ref> Concordantly, [[Geochemistry|geochemist]] Russell has proposed that "the purpose of life is to hydrogenate carbon dioxide" (as part of a "metabolism-first," rather than a "genetics-first," scenario).<ref name="Musser">{{cite web |url=http://blogs.scientificamerican.com/observations/how-life-arose-on-earth-and-how-a-singularity-might-bring-it-down/ |title=How Life Arose on Earth, and How a Singularity Might Bring It Down |last=Musser |first=George |authorlink=George Musser |date=23 September 2011 |work=Observations |type=Blog |accessdate=2015-06-17 |url-status=live |archiveurl=https://web.archive.org/web/20150617211804/http://blogs.scientificamerican.com/observations/how-life-arose-on-earth-and-how-a-singularity-might-bring-it-down/ |archivedate=17 June 2015}}</ref><ref name="Carroll">{{cite web |url=http://blogs.discovermagazine.com/cosmicvariance/2010/03/10/free-energy-and-the-meaning-of-life/ |title=Free Energy and the Meaning of Life |last=Carroll |first=Sean |authorlink=Sean M. Carroll |date=10 March 2010 |work=Cosmic Variance |type=Blog |publisher=Discover|accessdate=2015-06-17 |url-status=live |archiveurl=https://web.archive.org/web/20150714074327/http://blogs.discovermagazine.com/cosmicvariance/2010/03/10/free-energy-and-the-meaning-of-life/ |archivedate=14 July 2015}}</ref> [[Physicist]] [[Jeremy England]] has proposed that life was inevitable from general thermodynamic considerations: <blockquote>... when a group of atoms is driven by an external source of energy (like the sun or chemical fuel) and surrounded by a heat bath (like the ocean or atmosphere), it will often gradually restructure itself in order to dissipate increasingly more energy. This could mean that under certain conditions, matter inexorably acquires the key physical attribute associated with life.<ref>{{cite journal |last=Wolchover |first=Natalie |date=22 January 2014 |title=A New Physics Theory of Life |url=https://www.quantamagazine.org/20140122-a-new-physics-theory-of-life/ |journal=Quanta Magazine |accessdate=2015-06-17 |url-status=live |archiveurl=https://web.archive.org/web/20150613052830/https://www.quantamagazine.org/20140122-a-new-physics-theory-of-life/ |archivedate=13 June 2015}}</ref><ref>{{cite journal |last=England |first=Jeremy L. |authorlink=Jeremy England |date=28 September 2013 |title=Statistical physics of self-replication |url=http://www.englandlab.com/uploads/7/8/0/3/7803054/2013jcpsrep.pdf |journal=[[Journal of Chemical Physics]] |volume=139 |issue=12 |page=121923 |arxiv=1209.1179 |bibcode=2013JChPh.139l1923E |doi=10.1063/1.4818538 |pmid=24089735 |accessdate=2015-06-18 |url-status=live |archiveurl=https://web.archive.org/web/20150604131515/http://www.englandlab.com/uploads/7/8/0/3/7803054/2013jcpsrep.pdf |archivedate=4 June 2015|hdl=1721.1/90392 |s2cid=478964 }}</ref></blockquote>

One of the earliest incarnations of this idea was put forward in 1924 with Oparin's notion of primitive self-replicating vesicles which predated the discovery of the structure of DNA. Variants in the 1980s and 1990s include Wächtershäuser's iron–sulfur world theory and models introduced by [[Christian de Duve]] based on the chemistry of [[thioester]]s. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by [[Freeman Dyson]] in the early 1980s and [[Stuart Kauffman]]'s notion of collectively autocatalytic sets, discussed later that decade.

Orgel summarized his analysis by stating, <blockquote>There is at present no reason to expect that multistep cycles such as the reductive citric acid cycle will self-organize on the surface of FeS/FeS2 or some other mineral."<ref>{{cite journal |last=Orgel |first=Leslie E. |date=7 November 2000 |title=Self-organizing biochemical cycles |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=97 |issue=23 |pages=12503–12507 |bibcode=2000PNAS...9712503O |doi=10.1073/pnas.220406697|pmc=18793 |pmid=11058157}}</ref></blockquote> It is possible that another type of metabolic pathway was used at the beginning of life. For example, instead of the reductive citric acid cycle, the "open" [[acetyl-CoA]] pathway (another one of the five recognized ways of carbon dioxide fixation in nature today) would be compatible with the idea of self-organization on a metal sulfide surface. The key enzyme of this pathway, [[carbon monoxide dehydrogenase]]/[[CO-methylating acetyl-CoA synthase|acetyl-CoA synthase]], harbors mixed nickel-iron-sulfur clusters in its reaction centers and catalyzes the formation of acetyl-CoA (similar to acetyl-thiol) in a single step. There are increasing concerns, however, that prebiotic [[Thioacetic acid|thiolated]] and [[thioester]] compounds are thermodynamically and kinetically unfavorable to accumulate in presumed prebiotic conditions (i.e. hydrothermal vents).<ref>{{cite journal|last1=Chandru|first1=Kuhan|last2=Gilbert|first2=Alexis|last3=Butch|first3=Christopher|last4=Aono|first4=Masashi|last5=Cleaves|first5=Henderson James II|title=The Abiotic Chemistry of Thiolated Acetate Derivatives and the Origin of Life|journal=Scientific Reports|date=21 July 2016|volume=6|issue=29883|pages=29883|doi=10.1038/srep29883|pmid=27443234|pmc=4956751|bibcode=2016NatSR...629883C}}</ref> It has also been proposed that [[cysteine]] and [[homocysteine]] may have reacted with [[nitrile]]s resulting from the [[Strecker amino acid synthesis|Stecker reaction]], readily forming catalytic thiol-reach poplypeptides.<ref>{{Cite journal|last1=Vallee|first1=Yannick|last2=Shalayel|first2=Ibrahim|last3=Ly|first3=Kieu-Dung|last4=Rao|first4=K. V. Raghavendra|last5=Paëpe|first5=Gael De|last6=Märker|first6=Katharina|last7=Milet|first7=Anne|date=2017-11-08|title=At the very beginning of life on Earth: the thiol-rich peptide (TRP) world hypothesis|url=http://www.ijdb.ehu.es/web/paper/170028yv/at-the-very-beginning-of-life-on-earth-the-thiol-rich-peptide-trp-world-hypothesis|journal=International Journal of Developmental Biology|volume=61|issue=8–9|pages=471–478|doi=10.1387/ijdb.170028yv|pmid=29139533|doi-access=free}}</ref>

=== Zinc-world hypothesis ===

The zinc world (Zn-world) theory of Mulkidjanian<ref name="Mulkidjanian">{{cite journal |last=Mulkidjanian |first=Armen Y. |date=24 August 2009 |title=On the origin of life in the zinc world: 1. Photosynthesizing, porous edifices built of hydrothermally precipitated zinc sulfide as cradles of life on Earth |journal=Biology Direct |volume=4 |page=26 |doi=10.1186/1745-6150-4-26 |pmid=19703272 |pmc=3152778 }}</ref> is an extension of Wächtershäuser's pyrite hypothesis. Wächtershäuser based his theory of the initial chemical processes leading to informational molecules (RNA, peptides) on a regular mesh of electric charges at the surface of pyrite that may have facilitated the primeval [[polymerization]] by attracting reactants and arranging them appropriately relative to each other.<ref>{{cite journal |last=Wächtershäuser |first=Günter |date=December 1988 |title=Before Enzymes and Templates: Theory of Surface Metabolism |journal=[[Microbiology and Molecular Biology Reviews|Microbiological Reviews]] |volume=52 |pages=452–484 |issue=4 |pmc=373159 |pmid=3070320 |doi=10.1128/MMBR.52.4.452-484.1988 }}</ref> The Zn-world theory specifies and differentiates further.<ref name="Mulkidjanian" /><ref>{{cite journal |last1=Mulkidjanian |first1=Armen Y. |last2=Galperin |first2=Michael Y. |date=24 August 2009 |title=On the origin of life in the zinc world. 2. Validation of the hypothesis on the photosynthesizing zinc sulfide edifices as cradles of life on Earth |journal=Biology Direct |volume=4 |page=27 |doi=10.1186/1745-6150-4-27 |pmid=19703275 |pmc=2749021 }}</ref> Hydrothermal fluids rich in H2S interacting with cold primordial ocean (or Darwin's "warm little pond") water leads to the precipitation of metal sulfide particles. Oceanic [[Hydrothermal vent|vent systems]] and other hydrothermal systems have a zonal structure reflected in ancient [[Volcanogenic massive sulfide ore deposit|volcanogenic massive sulfide deposits]] (VMS) of hydrothermal origin. They reach many kilometers in diameter and date back to the [[Archean]] Eon. Most abundant are pyrite (FeS2), [[chalcopyrite]] (CuFeS2), and [[sphalerite]] (ZnS), with additions of [[galena]] (PbS) and [[alabandite]] (MnS). ZnS and MnS have a unique ability to store radiation energy, e.g. from UV light. During the relevant time window of the origins of replicating molecules, the primordial atmospheric pressure was high enough (>100 bar, about 100 atmospheres) to precipitate near the Earth's surface, and UV irradiation was 10 to 100 times more intense than now; hence the unique photosynthetic properties mediated by ZnS provided just the right energy conditions to energize the synthesis of informational and metabolic molecules and the selection of photostable nucleobases.

The Zn-world theory has been further filled out with experimental and theoretical evidence for the ionic constitution of the interior of the first proto-cells before archaea, bacteria and [[Origin of eukaryotes|proto-eukaryotes]] evolved. [[Archibald Macallum]] noted the resemblance of body fluids such as blood and lymph to seawater;<ref>{{cite journal |last=Macallum |first=A. B. |authorlink=Archibald Macallum |date=1 April 1926 |title=The Paleochemistry of the body fluids and tissues |journal=[[Physiological Reviews]] |volume=6 |issue=2 |pages=316–357|doi=10.1152/physrev.1926.6.2.316 }}</ref> however, the inorganic composition of all cells differ from that of modern seawater, which led Mulkidjanian and colleagues to reconstruct the "hatcheries" of the first cells combining geochemical analysis with [[Phylogenomics|phylogenomic]] scrutiny of the inorganic ion requirements of universal components of modern cells. The authors conclude that ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K+, Zn2+, Mn2+, and {{chem|[PO|4|]|3−}}. Geochemical reconstruction shows that the ionic composition conducive to the origin of cells could not have existed in what we today call marine settings but is compatible with emissions of vapor-dominated zones of what we today call inland geothermal systems. Under the oxygen depleted, CO2-dominated primordial atmosphere, the chemistry of water condensates and exhalations near geothermal fields would resemble the internal milieu of modern cells. Therefore, the precellular stages of evolution may have taken place in shallow "Darwin ponds" lined with porous [[silicate minerals]] mixed with metal sulfides and enriched in K+, Zn2+, and phosphorus compounds.<ref>{{cite journal |last1=Mulkidjanian |first1=Armen Y. |last2=Bychkov |first2=Andrew Yu. |last3=Dibrova |first3=Daria V. |last4=Galperin |first4=Michael Y. |last5=Koonin |first5=Eugene V. |display-authors=3 |date=3 April 2012 |title=Origin of first cells at terrestrial, anoxic geothermal fields |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=109 |issue=14 |pages=E821–E830 |bibcode=2012PNAS..109E.821M |doi=10.1073/pnas.1117774109 |pmc=3325685 |pmid=22331915}}</ref><ref>For a deeper integrative version of this hypothesis, see in particular {{harvnb|Lankenau|2011|pp=225–286}}, interconnecting the "Two RNA worlds" concept and other detailed aspects; and {{cite journal |last1=Davidovich |first1=Chen |last2=Belousoff |first2=Matthew |last3=Bashan |first3=Anat |last4=Yonath |first4=Ada |authorlink4=Ada Yonath |date=September 2009 |title=The evolving ribosome: from non-coded peptide bond formation to sophisticated translation machinery |journal=Research in Microbiology |volume=160 |issue=7 |pages=487–492 |doi=10.1016/j.resmic.2009.07.004 |pmid=19619641}}</ref>

==Other abiogenesis scenarios==

We define a scenario as a set of related concepts pertinent to the origin of life that is or has been investigated. The concepts related to the Iron-Sulfur world can be considered as a scenario. We consider some other scenarios that may partially overlap with scenarios discussed above or with each other.

===Chemical pathways described by computer===

In September 2020, chemists described, for the first time, possible chemical pathways from nonliving prebiotic chemicals to [[Biochemistry|complex biochemicals]] that could give rise to [[Earliest known life forms|living organisms]], based on a new computer program named ALLCHEMY.<ref name="SA-20200103">{{cite news |last=Starr |first=Michelle |title=A New Chemical 'Tree of The Origins of Life' Reveals Our Possible Molecular Evolution |url=https://www.sciencealert.com/a-new-chemical-tree-of-the-origins-of-life-reveals-our-possible-chemical-evolution |date=3 October 2020 |work=[[ScienceAlert]] |accessdate=3 October 2020 }}</ref><ref name="SCI-20200925">{{cite journal |author=Wolos, Agnieszka |display-authors=et al. |title=Synthetic connectivity, emergence, and self-regeneration in the network of prebiotic chemistry |url=https://science.sciencemag.org/content/369/6511/eaaw1955 |date=25 September 2020 |journal=[[Science (journal)|Science]] |volume=369 |issue=6511 |doi=10.1126/science.aaw1955 |doi-broken-date=10 October 2020 |pmid=32973002 |accessdate=3 October 2020 }}</ref>

===The hypercycle===

In the early 1970s, Manfred Eigen and [[Peter Schuster]] examined the transient stages between the molecular chaos and a self-replicating [[Hypercycle (chemistry)|hypercycle]] in a prebiotic soup.<ref>{{harvnb|Eigen|Schuster|1979}}</ref> In a hypercycle, the [[information]] storing system (possibly RNA) produces an [[enzyme]], which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create [[Quasispecies model|quasispecies]], which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery of [[ribozyme]]s capable of catalyzing their own chemical reactions. The hypercycle theory requires the existence of complex biochemicals, such as nucleotides, which do not form under the conditions proposed by the Miller–Urey experiment.

===Organic pigments in dissipative structures===

In his "Thermodynamic Dissipation Theory of the Origin and Evolution of Life",<ref>{{cite journal |bibcode=2011ESD.....2...37M |title= Thermodynamic Origin of Life |journal=Earth System Dynamics |volume=0907 |issue=2011 |pages=37–51 |last1=Michaelian |first1=K |year=2009 |arxiv=0907.0042 |doi=10.5194/esd-2-37-2011 |s2cid= 14574109 }}</ref><ref name="Michaelian, K. 2011">{{cite journal |doi=10.5194/esd-2-37-2011 |title= Thermodynamic dissipation theory for the origin of life |journal=Earth System Dynamics |volume=2 |issue=1 |pages=37–51 |year=2011 |last1= Michaelian |first1=K |bibcode=2011ESD.....2...37M |arxiv=0907.0042 |s2cid= 14574109 }}</ref><ref name="Michaelian, K. 2017">{{cite journal |doi= 10.1016/j.heliyon.2017.e00424 |pmid=29062973 |pmc=5647473 |title=Microscopic dissipative structuring and proliferation at the origin of life |journal=Heliyon |volume=3 |issue=10 |pages=e00424 |year=2017 |last1=Michaelian |first1=Karo }}</ref> Karo Michaelian has taken the insight of Boltzmann and the work of Prigogine to its ultimate consequences regarding the origin of life. This theory postulates that the hallmark of the origin and evolution of life is the microscopic dissipative structuring of [[Biological pigment|organic pigments]] and their proliferation over the entire Earth surface.<ref name="Michaelian, K. 2017" /> Present day life augments the entropy production of Earth in its solar environment by dissipating [[ultraviolet]] and [[Visible spectrum|visible]] [[photon]]s into heat through organic pigments in water. This heat then catalyzes a host of secondary dissipative processes such as the [[water cycle]], [[Ocean current|ocean]] and [[wind]] currents, [[Tropical cyclone|hurricanes]], etc.<ref name="Michaelian, K. 2011"/><ref name="HESS Opinions 'Biological catalysis"/> Michaelian argues that if the thermodynamic function of life today is to produce entropy through photon dissipation in organic pigments, then this probably was its function at its very beginnings. It turns out that both [[RNA]] and [[DNA]] when in water solution are very strong absorbers and extremely rapid dissipaters of ultraviolet light within the 230–290 nm wavelength (UV-C) region, which is a part of the Sun's spectrum that could have penetrated the prebiotic [[Atmosphere of Earth|atmosphere]].<ref>Sagan, C. (1973) Ultraviolet Selection Pressure on the Earliest Organisms, J. Theor. Biol., 39, 195–200.</ref> In fact, not only RNA and DNA, but many fundamental molecules of life (those common to all three [[Domain (biology)|domains]] of life) are also pigments that absorb in the UV-C, and many of these also have a chemical affinity to RNA and DNA.<ref>{{cite journal |doi=10.5194/bg-12-4913-2015 |title=Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum |journal=Biogeosciences |volume=12 |issue=16 |pages=4913–4937 |year=2015 |last1=Michaelian |first1=K |last2=Simeonov |first2=A |bibcode=2015BGeo...12.4913M |arxiv=1405.4059v2 }}</ref> [[Nucleic acid]]s may thus have acted as acceptor molecules to the UV-C photon [[Excited state|excited]] antenna pigment donor molecules by providing an [[Conical intersection|ultrafast channel]] for dissipation. Michaelian has shown using the formalism of non-linear irreversible thermodynamics that there would have existed during the [[Archean]] a thermodynamic imperative to the abiogenic UV-C [[Photochemistry|photochemical]] synthesis and proliferation of these pigments over the entire Earth surface if they acted as [[Catalysis|catalysts]] to augment the dissipation of the solar photons.<ref>{{cite journal |doi=10.1088/1742-6596/475/1/012010 |title=A non-linear irreversible thermodynamic perspective on organic pigment proliferation and biological evolution |journal= Journal of Physics: Conference Series |volume=475 |issue=1 |pages=012010 |year=2013 |last1=Michaelian |first1=K |bibcode= 2013JPhCS.475a2010M |arxiv=1307.5924 |s2cid=118564759 }}</ref> By the end of the Archean, with life-induced [[ozone]] dissipating UV-C light in the Earth's upper atmosphere, it would have become ever more improbable for a completely new life to emerge that did not rely on the complex metabolic pathways already existing since now the free energy in the photons arriving at Earth's surface would have been insufficient for direct breaking and remaking of [[covalent bond]]s. It has been suggested, however, that such changes in the surface flux of ultraviolet radiation due to geophysical events affecting the atmosphere could have been what promoted the development of complexity in life based on existing metabolic pathways, for example during the [[Cambrian explosion]]<ref>{{cite journal | last1 = Doglioni | first1 = C. | last2 = Pignatti | first2 = J. | last3 = Coleman | first3 = M. | year = 2016 | title = Why did life develop on the surface of the Earth in the Cambrian? | journal = Geoscience Frontiers | volume = 7 | issue = 6| pages = 865–873 | doi=10.1016/j.gsf.2016.02.001| url = https://iris.uniroma1.it/bitstream/11573/925124/1/Doglioni_Why_2016.pdf }}</ref>

Some of the most difficult problems concerning the origin of life, such as enzyme-less [[DNA replication|replication]] of RNA and DNA,<ref>{{cite journal |last1=Michaelian |first1=Karo |last2=Santillán |first2=Norberto |title=UVC photon-induced denaturing of DNA: A possible dissipative route to Archean enzyme-less replication |journal=Heliyon |date=June 2019 |volume=5 |issue=6 |page=e01902 |doi=10.1016/j.heliyon.2019.e01902|pmid=31249892 |pmc=6584779 }}</ref> [[homochirality]] of the fundamental molecules,<ref>{{cite journal |last1=Michaelian |first1=Karo |title=Homochirality through Photon-Induced Denaturing of RNA/DNA at the Origin of Life |journal=Life |date=June 2018 |volume=8 |issue=2 |page=21 |doi=10.3390/life8020021 |pmid=29882802 |pmc=6027432 }}</ref> and the origin of [[Genetic code|information encoding]] in RNA and DNA, also find an explanation within the same dissipative thermodynamic framework by considering the probable existence of a relation between primordial replication and UV-C photon dissipation. Michaelian suggests that it is erroneous to expect to describe the emergence, proliferation, or even evolution, of life without overwhelming reference to entropy production through the dissipation of a generalized thermodynamic potential, in particular, the prevailing solar photon flux.

===Protein amyloid===

A new origin-of-life theory based on self-replicating beta-sheet structures has been put forward by Maury in 2009.<ref>{{cite journal | last1 = Maury | first1 = CP | year = 2009 | title = Self-proagating beta-sheet polypeptide structures as prebiotic informational entities:The amyloid world | journal = Origins of Life and Evolution of Biospheres | volume = 39 | issue = 2| pages = 141–150 | doi = 10.1007/s11084-009-9165-6 | pmid = 19301141 | s2cid = 20073536 }}</ref><ref>{{cite journal | last1 = Maury | first1 = CP | year = 2015 | title = Origin of Life.Primordial genetics: Information transfer in a pre-RNA world based on self-replicating beta-sheet amyloid conformers | journal = Journal of Theoretical Biology | volume = 382 | pages = 292–297 | doi = 10.1016/j.jtbi.2015.07.008 | pmid = 26196585 | doi-access = free }}</ref> The theory suggest that self-replicating and self-assembling catalytic [[amyloid]]s were the first informational polymers in a primitive pre-RNA world. The main arguments for the ''amyloid hypothesis'' is based on the structural stability, autocatalytic and catalytic properties, and evolvability of beta-sheet based informational systems. Such systems are also error correcting<ref>{{cite journal | last1 = Nanda | first1 = J | last2 = Rubinov | first2 = B | last3 = Ivnitski | first3 = D | last4 = Mukherjee | first4 = R | last5 = Shtelman | first5 = E | last6 = Motro | first6 = Y | last7 = Miller | first7 = Y | last8 = Wagner | first8 = N | last9 = Cohen-Luria | first9 = R | last10 = Ashkenasy | first10 = G | year = 2017 | title = Emergence of native peptide seuqences in prebiotic replication networks | journal = Nature Communications | volume = 8 | issue = 1| page = 343 | doi = 10.1038/s41467-017-00463-1 | pmid = 28874657 | pmc = 5585222 | bibcode = 2017NatCo...8..434N }}</ref> and [[chiroselective]].<ref>{{cite journal | last1 = Rout | first1 = SK | last2 = Friedmann | first2 = MP | last3 = Riek | first3 = R | last4 = Greenwald | first4 = J | year = 2018 | title = A prebiotic templated-directed synthesis based on amyloids | journal = Nature Communications | volume = 9 | issue = 1| pages = 234–242 | doi = 10.1038/s41467-017-02742-3 | pmid = 29339755 | pmc = 5770463 }}</ref>



=== Fluctuating salinity: dilute and dry-down ===

Theories of abiogenesis seldom address the caveat raised by Harold Blum:<ref>Blum, H.F. (1957). On the origin of self-replicating systems. In Rhythmic and Synthetic Processes in Growth, ed. Rudnick, D., pp. 155–170. Princeton University Press, Princeton, NJ.</ref> if the key informational elements of life – proto-nucleic acid chains – spontaneously form duplex structures, then there is no way to dissociate them. <blockquote>Somewhere in this cycle work must be done, which means that free energy must be expended. If the parts assemble themselves on a template spontaneously, work has to be done to take the replica off; or, if the replica comes off the template of its own accord, work must be done to put the parts on in the first place.</blockquote>

The Oparin–Haldane conjecture addresses the formation, but not the dissociation, of nucleic acid polymers and duplexes. However, nucleic acids are unusual because, in the absence of counterions (low salt) to neutralize the high charges on opposing phosphate groups, the nucleic acid duplex dissociates into single chains.<ref name="ReferenceB">{{Cite journal |doi = 10.1016/j.icarus.2003.10.018|title = Fast tidal cycling and the origin of life|year = 2004|last1 = Lathe|first1 = Richard|journal = Icarus|volume = 168|issue = 1|pages = 18–22|bibcode = 2004Icar..168...18L}}</ref> Early tides, driven by a close moon, could have generated rapid cycles of dilution (high tide, low salt) and concentration (dry-down at low tide, high salt) that exclusively promoted the replication of nucleic acids<ref name="ReferenceB"/> through a process dubbed tidal chain reaction (TCR).<ref>{{Cite journal |doi = 10.1017/S1473550405002314|title = Tidal chain reaction and the origin of replicating biopolymers|year = 2005|last1 = Lathe|first1 = Richard|journal = International Journal of Astrobiology|volume = 4|issue = 1|pages = 19–31|bibcode = 2005IJAsB...4...19L}}</ref> This theory has been criticized on the grounds that early tides may not have been so rapid,<ref>{{Cite journal |doi = 10.1016/j.icarus.2005.04.022|title = Comment on the paper "Fast tidal cycling and the origin of life" by Richard Lathe|year = 2006|last1 = Varga|first1 = P.|last2 = Rybicki|first2 = K.|last3 = Denis|first3 = C.|journal = Icarus|volume = 180|issue = 1|pages = 274–276|bibcode = 2006Icar..180..274V}}</ref> although regression from current values requires an Earth–Moon juxtaposition at around two Ga, for which there is no evidence, and early tides may have been approximately every seven hours.<ref>{{Cite journal |doi = 10.1016/j.icarus.2005.08.019|title = Early tides: Response to Varga et al|year = 2006|last1 = Lathe|first1 = R.|journal = Icarus|volume = 180|issue = 1|pages = 277–280|bibcode = 2006Icar..180..277L}}</ref> Another critique is that only 2–3% of the Earth's crust may have been exposed above the sea until late in terrestrial evolution.<ref>{{Cite journal | doi=10.1016/j.epsl.2008.08.029| title=A case for late-Archaean continental emergence from thermal evolution models and hypsometry| year=2008| last1=Flament| first1=Nicolas| last2=Coltice| first2=Nicolas| last3=Rey| first3=Patrice F.| journal=Earth and Planetary Science Letters| volume=275| issue=3–4| pages=326–336| bibcode=2008E&PSL.275..326F}}</ref>

The TCR (tidal chain reaction) theory has mechanistic advantages over thermal association/dissociation at deep-sea vents because TCR requires that chain assembly (template-driven polymerization) takes place during the dry-down phase, when precursors are most concentrated, whereas thermal cycling needs polymerization to take place during the cold phase, when the rate of chain assembly is lowest and precursors are likely to be more dilute.

=== A first protein that condenses substrates during thermal cycling: thermosynthesis===

[[File:ConvectionCells.svg|thumb|upright=1.25|Convection cells in fluid placed in a gravity field are selforganizing and enable thermal cycling of the suspended contents in the fluid such as protocells containing protoenzymes that work on thermal cycling.]]

'''Emergence of chemiosmotic machinery''' Today's bioenergetic process of [[fermentation]] is carried out by either the aforementioned citric acid cycle or the Acetyl-CoA pathway, both of which have been connected to the primordial Iron–sulfur world.

In a different approach, the thermosynthesis hypothesis considers the bioenergetic process of [[chemiosmosis]], which plays an essential role in [[cellular respiration]] and photosynthesis, more basal than fermentation: the [[ATP synthase]] enzyme, which sustains chemiosmosis, is proposed as the currently extant enzyme most closely related to the first metabolic process.<ref>{{cite journal |last=Muller |first=Anthonie W. J. |date=7 August 1985 |pages=429–453 |title=Thermosynthesis by biomembranes: Energy gain from cyclic temperature changes |journal=[[Journal of Theoretical Biology]] |volume=115 |issue=3 |doi=10.1016/S0022-5193(85)80202-2 |pmid=3162066}}</ref><ref>{{cite journal |last=Muller |first=Anthonie W. J. |year=1995 |title=Were the first organisms heat engines? A new model for biogenesis and the early evolution of biological energy conversion |journal=Progress in Biophysics and Molecular Biology |volume=63 |issue=2 |pages=193–231 |doi=10.1016/0079-6107(95)00004-7 |pmid=7542789}}</ref>

First life needed an energy source to bring about the condensation reaction that yielded the peptide bonds of proteins and the [[phosphodiester bond]]s of RNA. In a generalization and thermal variation of the [[ATP synthase#Binding model|binding change mechanism]] of today's ATP synthase, the "first protein" would have bound substrates (peptides, phosphate, nucleosides, RNA 'monomers') and condensed them to a reaction product that remained bound until it was released after a temperature change by a thermal unfolding. The primordial '''first protein''' would therefore have strongly resembled the beta subunits of the [[ATP synthase alpha/beta subunits]] of today's F1 moiety in the FoF1 [[ATP synthase]]. Note however that today's enzymes function during isothermal conditions, whereas the hypothetical first protein worked on and during thermal cycling.

The energy source under the thermosynthesis hypothesis was thermal cycling, the result of suspension of protocells in a [[convection]] current, as is plausible in a volcanic hot spring; the convection accounts for the self-organization and [[Dissipative system|dissipative structure]] required in any origin of life model. The still ubiquitous role of thermal cycling in germination and cell division is considered a relic of primordial thermosynthesis.

By [[Phosphorylation|phosphorylating]] cell membrane lipids, this '''first protein''' gave a selective advantage to the lipid protocell that contained the protein. This protein also synthesized a library of many proteins, of which only a minute fraction had thermosynthesis capabilities. As proposed by Dyson,<ref name="Dyson 1999" /> it propagated functionally: it made daughters with similar capabilities, but it did not copy itself. Functioning daughters consisted of different amino acid sequences.

Category:Astrobiology

类别: 天体生物学

Whereas the iron–sulfur world identifies a circular pathway as the most simple, the thermosynthesis hypothesis does not even invoke a pathway: [[ATP synthase#Binding model|ATP synthase's binding change mechanism]] resembles a physical adsorption process that yields free energy,<ref>{{cite journal |last1=Muller |first1=Anthonie W. J. |last2=Schulze-Makuch |first2=Dirk |authorlink2=Dirk Schulze-Makuch |date=1 April 2006 |title=Sorption heat engines: Simple inanimate negative entropy generators |journal=[[Physica (journal)#Physica A: Statistical Mechanics and its Applications|Physica A: Statistical Mechanics and its Applications]] |volume=362 |issue=2 |pages=369–381 |arxiv=physics/0507173 |bibcode=2006PhyA..362..369M |doi=10.1016/j.physa.2005.12.003 |s2cid=96186464 }}</ref> rather than a regular enzyme's mechanism, which decreases the free energy.

Category:Evolutionarily significant biological phenomena

范畴: 具有进化意义的生物现象

Category:Evolutionary biology

分类: 进化生物学

The described first protein may be simple in the sense that is requires only a short sequence of conserved amino acid residues, a sequent sufficient for the appropriate catalytic cleft. In contrast, it has been claimed that the emergence of cyclic systems of protein catalysts such as required by fermentation is implausible because of the length of many required sequences.<ref>{{harvnb|Orgel|1987|pp=9–16}}</ref>

Life

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=== Pre-RNA world: The ribose issue and its bypass ===

Category:Prebiotic chemistry

类别: 生命前化学

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