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第172行： − 今天，一切生命的能量来源都可以与光合作用联系起来，人们称之为太阳光的初级生产。海洋底部热液喷口中的生物用于氧化还原性化合物的氧气，就来源于海洋表面光合作用。+ 第182行：
第186行： − + − − − − − 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}} − − 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世界假说描述了一个具有自我复制和催化能力的RNA，但没有DNA或蛋白质的早期地球。<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> 现在普遍认为现在地球上的生命起源于一个RNA世界，尽管基于RNA的生命可能并不是最早存在的生命。<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}}***缺乏对应英文***这个结论是由许多独立的证据得出的，例如观察到RNA是翻译过程的核心，并且小RNA可以催化生命所需的所有化学基团和信息转移。***缺乏对应英文***核糖体的结构被称为 "确凿的证据"，因为它表明核糖体是一个核酶，其核心是RNA，并且在催化肽键形成的活性位点18埃以内没有氨基酸侧链。 − − 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> − − 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世界的概念是由亚历山大·里奇Alexander Rich在1962年首次提出的<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> ，而这个术语则是由沃尔特·吉尔伯特Walter Gilbert在1986年创造的。<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>+ − 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. − + − + − − − 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> − − 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. − A very small minority of studies have concluded differently, namely that the root is in the domain Bacteria, either in the phylum Firmicutes or’’’<font color=’’#32CD32’’> that the phylum Chloroflexi is basal to a clade with Archaea+Eukaryotes and the rest of Bacteria as proposed by Thomas Cavalier-Smith. </font>’’’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.+ − 极少数的研究得出了不同的结论，即生命树的根部在细菌域中，要么在厚壁菌门中，要么是在绿弯菌门中，是古细菌+真核生物组成的一个演化枝和其余的细菌的基础，按照托马斯·卡弗利尔-史密斯Thomas Cavalier-Smith 所提出的那样。最近，彼得·沃德 Peter Ward 提出了另一种基于非生物的 RNA 合成的观点，该合成被包裹在一个胶囊中，然后产生RNA核酶复制品。有人提出，这然后在核糖核酸主导（RNA生命）之间分岔，在失去核酶RNA后病毒成为病毒主导，在脂质壁内形成一个大隔室，在20种氨基酸和三联子密码基础上形成DNA后成为细胞主导，它被确立为早期系统发育树的最后一个普遍共同祖先或LUCA。 + − 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个基因被识别为可能存在于生活在地球上的所有生物的最后一个普遍共同祖先（LUCA）中。对来自各种系统发育树的610万个原核生物蛋白编码基因进行了测序，从286,514个蛋白簇中识别了355个蛋白簇，它们很可能是LUCA共有的。结果+ − | doi = 10.1016/0079-6107(95)00004-7+ − + + + − ..说明LUCA是厌氧的、固定二氧化碳的、氢气依赖的且具有Wood-Ljungdahl通路的、固定氮气的和嗜热的。LUCA的生物化学中充斥着FeS簇和自由基反应机制。它的辅因子揭示了对过渡金属、黄素、S-腺苷甲硫氨酸、辅酶A、铁氧化还原蛋白、钼蝶呤、柯啉环和硒的依赖性。其遗传密码需要核苷修饰和S-腺苷甲硫氨酸依赖的甲基化"。+ − | 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 H<sub>2</sub>, CO<sub>2</sub> and iron. − − 结果显示在所研究的355个系统发育中，产甲烷的梭菌是一个基础演化枝，并表明LUCA栖息在厌氧热液喷口处且地理化学活性环境中富含氢气，二氧化碳和铁。 − − | 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细菌的600万个基因创建了系统发育树，并识别出了很可能存在于 LUCA 中的355个蛋白质家族。它们是基于一种固定二氧化碳和氮的厌氧代谢。这表明LUCA是在一个富含氢、二氧化碳和铁的环境中进化的。 − − ===Key issues in abiogenesis=== − 生物发生中的关键问题 − − ====What came first: protein or nucleic acids?==== − − 孰先孰后：蛋白质还是核酸？ − − 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> − − [[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 > − − 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. − − 蛋白质合成的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。祖先的核糖体很可能完全由RNA组成，尽管有些作用已经被蛋白质取代了。关于这个主题的主要剩余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 > − − 尤金·库宁Eugene Koonin 说， − < blockquote > − 尽管在实验和理论上做了大量的努力，但对于复制和翻译的起源，目前还没有令人信服的设想，而复制和翻译是共同构成了生物系统核心的关键过程，也是生物进化的明显先决条件。RNA世界概念可能为这一难题的解决提供了最好的机会，但迄今为止还不能充分说明高效RNA复制酶或翻译系统的出现。MWO["多世界合一"]版本的永恒膨胀的宇宙模型可能提出了解决这一难题的方法，因为在一个无限的多元宇宙中，有有限数量的不同的宏观历史（每个历史重复无限次），即使是高度复杂的系统的偶然出现，不仅是可能的，而且是不可避免的。 − + − − − See: [[Genetic code#Origin|Genetic code]]. − − See: Genetic code. − − 请参阅：遗传密码。 − − ====Error in translation catastrophe==== − 灾难性翻译错误 − − 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> − − 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Hoffmann已经证明，早期容易出错的翻译机制可以稳定地抵御曾被设想为对生命起源有问题的那种错误灾难，被称为 "奥格尔悖论"。 − − ====Homochirality==== − 同手性 − − {{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> − − 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. − − 同手性是指由手性单元组成的某些材料的几何均匀性。手性是指不可重叠的三维形态，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（"利手性"）：几乎没有例外，氨基酸是左旋的，而核苷酸和糖类是右旋的。手性分子可以合成，但在没有手性源或手性催化剂的情况下，它们是以两种对映体以50/50的混合物（称为外消旋混合物）形成的。已知从外消旋起始原料产生非外消旋混合物的机制包括：非对称物理定律，如弱电相互作用；非对称环境，如圆偏振光、石英晶体或地球自转引起的环境，外消旋合成过程中的统计波动，以及自发的对称性破缺。 − − 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> − − 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. − − 一旦建立，手性将被选择。群体中的一个小偏差（对映体过量）可以通过不对称自催化放大成一个大的偏差，如在Soai反应中。在不对称自催化中，催化剂是一个手性分子，这意味着手性分子正在催化自己的生产。最初的对映体过量，例如可以通过偏振光产生，然后允许更丰富的对映体超过其他对映体。 − − 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> − 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 Clark认为，同手性可能始于外太空，因为对默奇森 Murchison陨石上氨基酸的研究表明，L-丙氨酸的出现频率是其D形式的两倍多，L-谷氨酸是其D形式的三倍多。各种手性晶体表面也可以作为手性单体单元可能集中和组装成大分子的场所。在陨石上发现的化合物表明，生命的手性来源于非生物合成，因为陨石上的氨基酸表现出左手旋偏向，而糖类则主要表现出右手旋偏向，这与在生物体中发现的相同。+ − + − 有第一颗恒星的早期宇宙+ + − {{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>+ − 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. − 在宇宙大爆炸发生后不久，大约140亿年前，宇宙中存在的化学元素只有氢、氦和锂，这是周期表中最轻的三种元素。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大、寿命短，通过恒星核合成产生更重的元素。碳是目前宇宙中含量第四丰富的化学元素（仅次于氢、氦、氧），主要形成于白矮星，尤其是那些大于两个太阳质量的白矮星。+ − 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>+ − 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.+ − + − ===Emergence of the Solar System=== − 太阳系的出现 − 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.+ + − 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，太阳系的形成和演化始于46亿年前，因为一个巨大的分子云的一小部分的引力塌缩。大部分塌缩的质量聚集在中心，形成了太阳，而其余的则压平成一个原行星盘，行星、卫星、小行星和其他小太阳系天体就是从这个原行星盘中形成的。+ − + − 地球的出现 − 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" /> − 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." − 地球，形成于45亿年前，起初是不适合任何生物体生存的。根据对地质学时间尺度的大量观察和研究，人们认为冥古代地球曾有过一个次级大气层，是通过小行星撞击物所积累的岩石脱气而形成的。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，生命就是在这种有利于有机分子形成的还原性条件下开始的。根据后来的模型，通过对古代矿物的研究提出，冥古代晚期的大气层主要由水蒸气、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。在地球形成过程中，地球失去了其初始质量的很大一部分，原行星盘中较重的岩石元素组成的核仍然存在。因此，地球缺乏在大气层中容纳任何氢分子的引力，并且在冥古代迅速失去了它，以及大部分的原始惰性气体.。二氧化碳在水中形成的溶液被认为使海洋呈微酸性，使海洋的pH值约为5.5。当时的大气层被描述为 "巨大的、高产的露天化学实验室。"***缺乏对应英文：它可能与今天火山释放的混合气体相似，它仍然支持一些非生物化学。***+ − ===Emergence of the ocean=== − 海洋的出现 − + − ===Late heavy bombardment=== − 晚期重型轰炸 − 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>+ − + − 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. − + − 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> − + − + − + − 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> − +
→当前的生命，生物发生的结果：生物学
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.
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.
现在越来越多的人或普遍认为，如果一个实体有能力进行三种基本的功能活动：新陈代谢、自我修复，和复制，那么它就被认为是“有生命的”。
现在越来越多的人或普遍认为，如果一个实体有能力进行三种基本的功能活动：新陈代谢、自我修复，和复制，那么它就被认为是“有生命的”。<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>
</blockquote>
相比之下，德克·舒尔茨-马库奇Dirk Schulze-Makuch 和 路易斯·欧文 Louis Irwin 在他们的书中花了整整第一章来讨论这个问题。
相比之下，德克·舒尔茨-马库奇 Dirk Schulze-Makuch和路易斯·欧文 Louis Irwin在他们的书中花了整整第一章来讨论这个问题。<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>
Nonetheless, a definition of life currently favored by [[NASA]] is that life is “a self-sustaining chemical system capable of Darwinian evolution.”<ref name="NASA-20210306">{{cite news |last=Voytek |first=Mary a. |title=About Life Detection |url=https://astrobiology.nasa.gov/research/life-detection/about/ |date=6 March 2021 |work=[[NASA]] |access-date=8 March 2021 }}</ref><ref name="NG-20201214">{{cite news |last=Marshall |first=Michael |title=He may have found the key to the origins of life. So why have so few heard of him? - Hungarian biologist Tibor Gánti is an obscure figure. Now, more than a decade after his death, his ideas about how life began are finally coming to fruition. |url=https://www.nationalgeographic.com/science/2020/12/he-may-have-found-the-key-to-origins-of-life-tibor-ganti-chemoton/ |date=14 December 2020 |work=[[National Geographic Society]] |access-date=8 March 2021 }}</ref><ref name="SPC-20130801">{{cite news |last=Mullen |first=Lesle |title=Defining Life: Q&A with Scientist Gerald Joyce |url=https://www.space.com/22210-life-definition-gerald-joyce-interview.html |date=1 August 2013 |work=[[Space.com]] |access-date=8 March 2021 }}</ref><ref name="NYT-20210226">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |title=The Secret Life of a Coronavirus - An oily, 100-nanometer-wide bubble of genes has killed more than two million people and reshaped the world. Scientists don't quite know what to make of it. |url=https://www.nytimes.com/2021/02/26/opinion/sunday/coronavirus-alive-dead.html |date=26 February 2021 |access-date=8 March 2021 }}</ref> More simply, life is, "matter that can reproduce itself and evolve as survival dictates".<ref name="ETSU-2012a">{{cite web |last=Luttermoser |first=Donald G. |title=ASTR-1020: Astronomy II Course Lecture Notes Section XII |url=http://faculty.etsu.edu/lutter/courses/astr1020/a1020chap12.pdf |date=2012 |work=[[East Tennessee State University]] |archive-url=https://web.archive.org/web/20170707114650/http://faculty.etsu.edu/lutter/courses/astr1020/a1020chap12.pdf |access-date=8 March 2021 |archive-date=7 July 2017 }}</ref><ref name="ETSU-2012b">{{cite web |last=Luttermoser |first=Donald G. |title=Physics 2028: Great Ideas in Science: The Exobiology Module |url=http://faculty.etsu.edu/lutter/courses/phys2028/p2028exobnotes.pdf |date=2012 |work=[[East Tennessee State University]] |archive-url=https://web.archive.org/web/20160412201815/http://faculty.etsu.edu/lutter/courses/phys2028/p2028exobnotes.pdf |access-date=8 March 2021 |archive-date=12 April 2016 }}</ref><ref name="ETSU-2012c">{{cite web |last=Luttermoser |first=Donald G. |title=Lecture Notes for ASTR 1020 - Astronomy II with Luttermoser at East Tennessee (ETSU) |url=http://www.koofers.com/files/notes-gyw4cx4ar4/ |date=2012 |work=[[East Tennessee State University]] |archive-url=https://web.archive.org/web/20120502172318/http://www.koofers.com/files/notes-gyw4cx4ar4/ |access-date=8 March 2021 |archive-date=2 May 2012 }}</ref>
====发酵====
====发酵====
连Peter Mitchell自己也认为发酵先于化学渗透。然而，化学渗透在生命中无处不在。一个依据化学渗透的生命起源模型已经被提出来了。
连Peter Mitchell自己也认为发酵先于化学渗透。然而，化学渗透在生命中无处不在。一个依据化学渗透的生命起源模型已经被提出来了。<ref>{{cite journal | author = Anthonie W.J. Muller | 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 | pages=193–231 | doi = 10.1016/0079-6107(95)00004-7 | pmid = 7542789 | issue = 2| doi-access = free }}</ref><ref>{{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 | volume = 36 | issue = 2 | year=2006 | pages=77–189 | pmid = 16642267 | doi =10.1007/s11084-005-9003-4|bibcode = 2006OLEB...36..177M }}</ref>
今天，一切生命的能量来源都可以与光合作用联系起来，人们称之为太阳光的初级生产。海洋底部热液喷口中的生物用于氧化还原性化合物<ref name="Schmidt-Rohr 20">Schmidt-Rohr, K. (2020). "Oxygen Is the High-Energy Molecule Powering Complex Multicellular Life: Fundamental Corrections to Traditional Bioenergetics'' ''ACS Omega'' '''5''': 2221-2233. http://dx.doi.org/10.1021/acsomega.9b03352</ref> 的氧气，就来源于海洋表面光合作用。
[[File:010 small subunit-1FKA.gif|thumb|upright=1.25|Molecular structure of the [[30S|ribosome 30S subunit]] from ''[[Thermus thermophilus]]''. 嗜热细菌核糖体30S亚基的分子结构。蛋白质显示为蓝色，单个RNA链显示为橙色。 <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.]]
[[File:010 small subunit-1FKA.gif|thumb|upright=1.25|嗜热细菌核糖体30S亚基的分子结构。 <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>蛋白质显示为蓝色，单个RNA链显示为橙色。 ]]
RNA世界假说描述了一个具有自我复制和催化能力的RNA，但没有DNA或蛋白质的早期地球。<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> 现在普遍认为现在地球上的生命起源于一个RNA世界，尽管基于RNA的生命可能并不是最早存在的生命。<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}}这个结论是由许多独立的证据得出的，例如观察到RNA是翻译过程的核心，并且小RNA可以催化生命所需的所有化学基团和信息转移。核糖体的结构被称为 "确凿的证据 smoking gun"，因为它表明核糖体是一个核酶，其核心是RNA，并且在催化肽键形成的活性位点18埃以内没有氨基酸侧链。<ref name="Robertson2012">{{cite journal |last1=Robertson |first1=Michael P. |last2=Joyce |first2=Gerald F. |author-link2=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><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) |page=a003483 |doi=10.1101/cshperspect.a003483 |pmid=20534711|pmc=2926754 |doi-access=free }}</ref> 尽管如此，在 2021 年 3 月，研究人员报告的证据表明，转移 RNA 的初步形式可能是生命早期发展中的复制分子本身。<ref name="EL-20210302">{{cite journal |last1=Kühnlein |first1=Alexandra |last2=Lanzmich |first2=Simon A. |last3=Brun |first3=Dieter |title=tRNA sequences can assemble into a replicator |doi=10.7554/eLife.63431 |date=2 March 2021 |journal=[[eLife]] |volume=10 |pmid=33648631 |pmc=7924937 |doi-access=free }}</ref><ref name="STD-20210403">{{cite news |last=Maximilian |first=Ludwig |title=Solving the Chicken-and-the-Egg Problem – "A Step Closer to the Reconstruction of the Origin of Life" |url=https://scitechdaily.com/solving-the-chicken-and-the-egg-problem-a-step-closer-to-the-reconstruction-of-the-origin-of-life/ |date=3 April 2021 |work=[[SciTech (magazine)|SciTechDaily]] |access-date=3 April 2021 }}</ref>
在2020年3月，天文学家户谷友则 Tomonori Totani提出了一种统计方法，用于解释初始的活性RNA分子是如何在宇宙大爆炸后某个时间随机产生的。<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>
RNA世界的概念是由亚历山大·里奇Alexander Rich在1962年首次提出的<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> ，而这个术语则是由沃尔特·吉尔伯特Walter Gilbert在1986年创造的。<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> 在2020年3月，天文学家户谷友则 Tomonori Totani提出了一种统计方法，用于解释初始的活性RNA分子是如何在宇宙大爆炸后某个时间随机产生的。<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>
===系统发育和最后的普遍共同祖先 Phylogeny and LUCA===
===系统发育和最后的普遍共同祖先 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 一个描述出现在生命系统发育树基部的火山热泉中的极端超嗜热菌的进化分枝图。]]]]
[[File:Phylogenic Tree-en.svg|upright=1.65|thumb|一个描述出现在生命系统发育树基部的火山热泉中的极端超嗜热菌的进化分枝图。]]]]
根据从卡尔·沃斯 Carl Woese 开始的一些分子研究，对于生命树的根部的位置，最普遍接受的观点是位于单系域细菌和一个由古细菌和真核生物组成的演化枝之间，这被称为“传统生命树”。<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>
根据从卡尔·沃斯 Carl Woese 开始的一些分子研究，对于生命树的根部的位置，最普遍接受的观点是位于单系域细菌和一个由古细菌和真核生物组成的演化枝之间，这被称为“传统生命树”。<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>
2016年，一组355个基因被识别为可能存在于生活在地球上的所有生物的最后一个'''普遍共同祖先 Last Universal Common Ancestor（LUCA）'''中。对来自各种系统发育树的610万个原核生物蛋白编码基因进行了测序，从286,514个蛋白簇中识别了355个蛋白簇，它们很可能是LUCA共有的。结果说明LUCA是厌氧的、固定二氧化碳的、氢气依赖的且具有Wood-Ljungdahl通路的、固定氮气的和嗜热的。LUCA的生物化学中充斥着FeS簇和自由基反应机制。它的辅因子揭示了对过渡金属、黄素、S-腺苷甲硫氨酸、辅酶A、铁氧化还原蛋白、钼蝶呤、柯啉环和硒的依赖性。其遗传密码需要核苷修饰和S-腺苷甲硫氨酸依赖的甲基化"。
===生物发生中的关键问题===
====孰先孰后：蛋白质还是核酸？====
蛋白质合成的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。祖先的核糖体很可能完全由RNA组成，尽管有些作用已经被蛋白质取代了。关于这个主题的主要剩余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。<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>
< blockquote >. . . depict LUCA as anaerobic, CO<sub>2</sub>-fixing, H<sub>2</sub>-dependent with a Wood–Ljungdahl pathway, N<sub>2</sub>-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."
尤金·库宁 Eugene Koonin 说，
<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.
尽管在实验和理论上做了大量的努力，但对于复制和翻译的起源，目前还没有令人信服的设想，而复制和翻译是共同构成了生物系统核心的关键过程，也是生物进化的明显先决条件。RNA世界概念可能为这一难题的解决提供了最好的机会，但迄今为止还不能充分说明高效RNA复制酶或翻译系统的出现。MWO["多世界合一"]版本的永恒膨胀的宇宙模型可能提出了解决这一难题的方法，因为在一个无限的多元宇宙中，有有限数量的不同的宏观历史（每个历史重复无限次），即使是高度复杂的系统的偶然出现，不仅是可能的，而且是不可避免的。<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 >
</blockquote >
====Emergence of the genetic code====
====遗传密码的出现====
遗传密码的出现
请参阅：[[遗传密码]]。
====灾难性翻译错误====
===Early universe with first stars===
霍夫曼 Hoffmann已经证明，早期容易出错的翻译机制可以稳定地抵御曾被设想为对生命起源有问题的那种错误灾难，被称为 "奥格尔悖论 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>
====同手性====
同手性是指由手性单元组成的某些材料的几何均匀性。手性是指不可重叠的三维形态，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（"利手性"）：几乎没有例外，<ref>{{harvnb|Chaichian|Rojas|Tureanu|2014|pp=353–364}}</ref>氨基酸是左旋的，而核苷酸和糖类是右旋的。手性分子可以合成，但在没有手性源或手性催化剂的情况下，它们是以两种对映体以50/50的混合物（称为外消旋混合物）形成的。已知从外消旋起始原料产生非外消旋混合物的机制包括：非对称物理定律，如弱电相互作用；非对称环境，如圆偏振光、石英晶体或地球自转引起的环境，外消旋合成过程中的统计波动，<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>以及自发的对称性破缺。<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>
一旦建立，手性将被选择。<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>群体中的一个小偏差（对映体过量）可以通过不对称自催化放大成一个大的偏差，如在Soai反应中。<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>在不对称自催化中，催化剂是一个手性分子，这意味着手性分子正在催化自己的生产。最初的对映体过量，例如可以通过偏振光产生，然后允许更丰富的对映体超过其他对映体。<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>
克拉克 Clark认为，同手性可能始于外太空，因为对默奇森 Murchison陨石上氨基酸的研究表明，L-丙氨酸的出现频率是其D形式的两倍多，L-谷氨酸是其D形式的三倍多。各种手性晶体表面也可以作为手性单体单元可能集中和组装成大分子的场所。<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>在陨石上发现的化合物表明，生命的手性来源于非生物合成，因为陨石上的氨基酸表现出左手旋偏向，而糖类则主要表现出右手旋偏向，这与在生物体中发现的相同。<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>
===有第一颗恒星的早期宇宙===
在宇宙大爆炸发生后不久，大约140亿年前，宇宙中存在的化学元素只有氢、氦和锂，这是周期表中最轻的三种元素。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大、寿命短，通过恒星核合成产生更重的元素。碳是目前宇宙中含量第四丰富的化学元素（仅次于氢、氦、氧），主要形成于白矮星，尤其是那些大于两个太阳质量的白矮星。<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>
当这些恒星达到其生命周期的终点时，它们在整个宇宙中喷射出这些较重的元素，其中包括碳和氧。这些较重的元素使得新的物体得以形成，包括岩质行星和其他天体。
当这些恒星达到其生命周期的终点时，它们在整个宇宙中喷射出这些较重的元素，其中包括碳和氧。这些较重的元素使得新的物体得以形成，包括岩质行星和其他天体。<ref>{{Cite web | url=https://wmap.gsfc.nasa.gov/universe/uni_life.html |title = WMAP- Life in the Universe}}</ref>
===太阳系的出现===
根据星云假说，太阳系的形成和演化始于46亿年前，因为一个巨大的分子云的一小部分的引力塌缩。<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>大部分塌缩的质量聚集在中心，形成了太阳，而其余的则压平成一个原行星盘，行星、卫星、小行星和其他小太阳系天体就是从这个原行星盘中形成的。
===地球的出现===
===Emergence of Earth===
地球，形成于45亿年前，起初是不适合任何生物体生存的。根据对地质学时间尺度的大量观察和研究，人们认为冥古代地球曾有过一个次级大气层，是通过小行星撞击物所积累的岩石脱气而形成的。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，生命就是在这种有利于有机分子形成的还原性条件下开始的。根据后来的模型，通过对古代矿物的研究提出，冥古代晚期的大气层主要由水蒸气、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。<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>在地球形成过程中，地球失去了其初始质量的很大一部分，原行星盘中较重的岩石元素组成的核仍然存在。<ref>{{harvnb|Fesenkov|1959|p=9}}</ref>因此，地球缺乏在大气层中容纳任何氢分子的引力，并且在冥古代迅速失去了它，以及大部分的原始惰性气体.。二氧化碳在水中形成的溶液被认为使海洋呈微酸性，使海洋的pH值约为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> 当时的大气层被描述为 "巨大的、高产的露天化学实验室。"它可能与今天火山释放的混合气体相似，它仍然支持一些非生物化学。<ref name="Follmann2009" />
===海洋的出现===
Oceans may have 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.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.
Oceans may have 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.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.
海洋可能最早出现在冥古宙，即地球形成后的2亿年，在一个100 C的高温的还原性环境中，pH值约为5.8，迅速上升到中性。这一假设已经得到了来自澳大利亚西部纳里尔山变质石英岩的4.404 Gyo锆石晶体的年代测定的支持。这一设想已经得到了来自澳大利亚西部的皮尔巴拉的杰克高地的纳瑞耶山的变质石英岩的44.04亿年前的锆石晶体的年代测定的支持，它提供了地球形成后1.5亿年前内存在海洋和大陆地壳的证据。尽管可能增加了火山活动，并存在许多较小的构造 "板块"，但有人认为，在44-43亿年之间，地球是一个水世界，几乎没有大陆地壳，大气层极度动荡，水圈受到来自T金牛座阶段的太阳的强烈的紫外线(UV)照射、宇宙辐射和持续的天体撞击。
海洋可能最早出现在冥古宙，即地球形成后的2亿年，在一个100 C的高温的还原性环境中，pH值约为5.8，迅速上升到中性。.<ref>{{cite journal |last1=Morse |first1=John W. |last2=MacKenzie |first2=Fred T. |author-link2=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>这一假设已经得到了来自澳大利亚西部纳里尔山变质石英岩的4.404 Gyo锆石晶体的年代测定的支持。这一设想已经得到了来自澳大利亚西部的皮尔巴拉的杰克高地的纳瑞耶山的变质石英岩的44.04亿年前的锆石晶体的年代测定的支持，它提供了地球形成后1.5亿年前内存在海洋和大陆地壳的证据。<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 |access-date=2015-06-03 |url-status=live |archive-url=https://web.archive.org/web/20150605132344/http://www.geology.wisc.edu/~valley/zircons/Wilde2001Nature.pdf |archive-date=5 June 2015|bibcode=2001Natur.409..175W |s2cid=4319774 }}</ref>尽管可能增加了火山活动，并存在许多较小的构造 "板块"，但有人认为，在44-43亿年之间，地球是一个水世界，几乎没有大陆地壳，大气层极度动荡，水圈受到来自T金牛座阶段的太阳的强烈的紫外线(UV)照射、宇宙辐射和持续的天体撞击。<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 |author-link5=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 |access-date=2015-06-08 |url-status=live |archive-url=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 |archive-date=14 July 2015|bibcode=2006PPP...232...99R }}</ref>由于地核和地幔之间的重力分选导致的内部加热会引起大量的地幔对流，这可能导致比现在存在的更小、更活跃的构造板块。
===晚期重型轰炸===
冥古代的环境对现代生命将是非常危险的。与直径达500公里的大型物体频繁碰撞，足以在撞击后的几个月内使地球成为不毛之地，并使海洋汽化，热蒸汽与岩石蒸汽混合，成为足以完全覆盖地球的高空云层。几个月后，这些云层的高度会开始降低，但在接下来的大约一千年里，云层的底部仍会升高。在那之后，低海拔地区就会开始下雨。在接下来的两千年里，雨水会慢慢地拉低云层的高度，使海洋只有在撞击事件发生3000年后才恢复到原来的深度。
冥古代的环境对现代生命将是非常危险的。与直径达500公里的大型物体频繁碰撞，足以在撞击后的几个月内使地球成为不毛之地，并使海洋汽化，热蒸汽与岩石蒸汽混合，成为足以完全覆盖地球的高空云层。几个月后，这些云层的高度会开始降低，但在接下来的大约一千年里，云层的底部仍会升高。在那之后，低海拔地区就会开始下雨。在接下来的两千年里，雨水会慢慢地拉低云层的高度，使海洋只有在撞击事件发生3000年后才恢复到原来的深度。<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>
传统上认为，在42.8亿年前到38亿年前之间的时期，巨行星轨道的变化可能造成了小行星和彗星对月球和其他内行星（水星、火星，大概还有地球和金星）的猛烈轰击。如果生命在那之前出现的话，这很可能会使这个星球反复成为不毛之地。从地质学上来说，冥古代地球会比历史上任何其他时间都要活跃得多。对陨石的研究表明，放射性同位素，如半衰期为7.17 千年的铝-26和半衰期为12.5亿年的钾-40，这些主要产生于超新星的同位素更为常见。由于地核和地幔之间的重力分选而产生的内部加热会引起大量的地幔对流，其结果可能是产生了比现在更小、更活跃的构造板块。
传统上认为，在42.8亿<ref name="NAT-20170301" /><ref name="NYT-20170301" /> 年前到38亿年前之间的时期，巨行星轨道的变化可能造成了小行星和彗星<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>对月球和其他内行星（水星、火星，大概还有地球和金星）的猛烈轰击。如果生命在那之前出现的话，这很可能会使这个星球反复成为不毛之地。<ref name="Follmann2009" />从地质学上来说，冥古代地球会比历史上任何其他时间都要活跃得多。对陨石的研究表明，放射性同位素，如半衰期为7.17 千年的铝-26和半衰期为12.5亿年的钾-40，这些主要产生于超新星的同位素更为常见<ref>{{harvnb|Davies|2007|pp=61–73}}</ref> 。由于地核和地幔之间的重力分选而产生的内部加热会引起大量的地幔对流，其结果可能是产生了比现在更小、更活跃的构造板块。
这种毁灭性的环境事件之间的时间段，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，那么自然发生可能早在40-42亿年前就发生了。如果地点在地球表面，那么自然发生只能发生在37-40亿年前之间。
这种毁灭性的环境事件之间的时间段，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，那么自然发生可能早在40-42亿年前就发生了。如果地点在地球表面，那么自然发生只能发生在37-40亿年前之间。<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>
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>
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.
对这些来源的有机物的产生的估计表明，在35亿年前之前，早期大气层内的晚期重型轰炸使可获得的有机物的数量与陆地来源产生的有机物数量相当。
对这些来源的有机物的产生的估计表明，在35亿年前之前，早期大气层内的晚期重型轰炸使可获得的有机物的数量与陆地来源产生的有机物数量相当。<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>
据估计，晚期重型轰炸还可能对数十米深的地球表面进行了有效的灭菌。如果生命进化到比这更深的地方，它也会被屏蔽在太阳进化的T金牛座阶段的早期高水平紫外线辐射之外。对地热加热的海洋地壳进行模拟，得到的有机物远比Miller–Urey实验中发现的多。在深层热液喷口中，埃弗雷特·休克 Everett Shock发现 "存在着形成有机化合物的巨大热力学驱动力，因为海水和热液远未达到平衡，混合并向更稳定的状态发展。"Shock发现，可用的能量在100-150 C左右达到最大，而这正是发现嗜热细菌和嗜热古细菌的温度，处于最接近最后普遍共同祖先（LUCA）的生命系统发育树的底部。
据估计，晚期重型轰炸还可能对数十米深的地球表面进行了有效的灭菌。如果生命进化到比这更深的地方，它也会被屏蔽在太阳进化的T金牛座阶段的早期高水平紫外线辐射之外。对地热加热的海洋地壳进行模拟，得到的有机物远比Miller–Urey实验中发现的多。在深层热液喷口中，埃弗雷特·休克 Everett Shock发现 "存在着形成有机化合物的巨大热力学驱动力，因为海水和热液远未达到平衡，混合并向更稳定的状态发展。"<ref>{{harvnb|Davies|1999|p=155}}</ref>Shock发现，可用的能量在100-150 C左右达到最大，而这正是发现嗜热细菌和嗜热古细菌的温度，处于最接近最后普遍共同祖先（LUCA）的生命系统发育树的底部。<ref>{{harvnb|Bock|Goode|1996}}</ref>
== 生命的最早证据：古生物学==
== 生命的最早证据：古生物学==