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{{Evolutionary biology}}
The '''history of life''' on [[Earth]] traces the processes by which living and [[fossil]] [[organism]]s evolved, from the earliest [[Abiogenesis|emergence of life]] to present day. Earth formed about 4.5 billion years ago (abbreviated as ''Ga'', for ''[[Year#SI prefix multipliers|gigaannum]]'') and evidence suggests that life emerged prior to 3.7 Ga.<ref name="Pearce 343–364">{{cite journal |last1=Pearce |first1=Ben K.D. |last2=Tupper |first2=Andrew S. |last3=Pudritz |first3=Ralph E. |author3-link=Ralph Pudritz |last4=Higgs |first4=Paul G. |display-authors=3 |date=March 1, 2018 |title=Constraining the Time Interval for the Origin of Life on Earth |journal=[[Astrobiology (journal)|Astrobiology]] |volume=18 |issue=3 |pages=343–364 |arxiv=1808.09460 |s2cid=4419671 |bibcode=2018AsBio..18..343P |doi=10.1089/ast.2017.1674 |issn=1531-1074 |pmid=29570409}}</ref><ref name="Rosing 674–676">{{cite journal |last=Rosing |first=Minik T. |date=January 29, 1999 |title=<sup>13</sup>C-Depleted Carbon Microparticles in &gt;3700-Ma Sea-Floor Sedimentary Rocks from West Greenland |journal=[[Science (journal)|Science]] |volume=283 |issue=5402 |pages=674–676 |bibcode=1999Sci...283..674R |doi=10.1126/science.283.5402.674 |issn=0036-8075 |pmid=9924024}}</ref><ref name="Ohtomo 25–28">{{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 |issn=1752-0894}}</ref> AlthoughThe theresimilarities isamong someall evidenceknown ofpresent-day life[[species]] asindicate earlythat asthey 4.1have todiverged 4.28 Ga, it remains controversial due tothrough the possible non-biological formationprocess of the purported fossils.<ref name="Pearce 343–364"/><ref>{{cite journal |last1=Papineau |first1=Dominic |last2=De Gregorio |first2=Bradley T. |last3=Cody |first3=George D. |last4=O'Neil |first4=J. |last5=Steele |first5=A. |last6=Stroud |first6=R. M. |last7=Fogel |first7=M. L. |display-authors=3 |date=June 2011 |title=Young poorly crystalline graphite in the &gt;3.8-Gyr-old Nuvvuagittuq banded iron formation |journal=[[Nature Geoscienceevolution]] |volume=4 |issue=6 |pages=376–379 |bibcode=2011NatGe...4..376P |doi=10.1038/ngeo1155 |issn=1752-0894}}</ref><ref name="PNAS-20151124-pdf">{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnke |first2=Patrick |last3=Harrison |first3=T. Mark |last4=Mao |first4=Wendy L. |display-authors=3 |date=November 24, 2015 |title=Potentially biogenic carbon preserved infrom a 4.1 billion-year-old zircon |url=https://www.pnas.org/content/pnas/early/2015/10/14/1517557112.full.pdf |url-status=live |journal=[[Proceedingscommon of the National Academy of Sciencesancestor]] |volume=112 |issue=47 |pages=14518–14521 |bibcode=2015PNAS..11214518B |doi=10.1073/pnas.1517557112 |issn=0027-8424 |pmc=4664351 |pmid=26483481 |archive-url=https://web.archive.org/web/20200213002627/https://www.pnas.org/content/pnas/early/2015/10/14/1517557112.full.pdf |archive-date=2020-02-13 |access-date=2020-02-14 |doi-access=free}}</ref><ref>{{cite journal harvnb|last1=Nemchin |first1=Alexander A. |last2=Whitehouse |first2=Martin J. |last3=Menneken |first3=Martina |last4=Geisler |first4=Thorsten |last5=Pidgeon |first5=Robert T. |last6=Wilde |first6=Simon A. |display-authors=3 |date=July 3, 2008 |title=A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills |journal=[[Nature (journal)|Nature]] |volume=454 |issue=7200 |pages=92–95 |bibcode=2008Natur.454...92N |s2cid=4415308 |doi=10.1038/nature07102 |issn=0028-0836 Futuyma|pmid=185968082005}}</ref>
 
The earliest clear evidence of life comes from [[biogenic substance|biogenic]] [[Δ13C|carbon signatures]]<ref name="Rosing 674–676" /><ref name="Ohtomo 25–28" /> and [[stromatolite]] fossils<ref>{{cite journal |last1=Nutman |first1=Allen P. |last2=Bennett |first2=Vickie C. |last3=Friend |first3=Clark R.L. |last4=Van Kranendonk |first4=Martin J. |last5=Chivas |first5=Allan R. |display-authors=3 |date=September 22, 2016 |title=Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures |url=https://ro.uow.edu.au/cgi/viewcontent.cgi?article=5181&context=smhpapers |url-status=live |format=PDF |journal=[[Nature (journal)|Nature]] |volume=537 |issue=7621 |pages=535–538 |bibcode=2016Natur.537..535N |s2cid=205250494 |doi=10.1038/nature19355 |issn=0028-0836 |pmid=27580034 |archive-url=https://web.archive.org/web/20200102053302/https://ro.uow.edu.au/cgi/viewcontent.cgi?article=5181&context=smhpapers |archive-date=2020-01-02 |access-date=2020-02-17}}</ref> discovered in 3.7 billion-year-old [[metasediment]]ary rocks from western [[Greenland]]. In 2015, possible "remains of [[biotic material|biotic life]]" were found in 4.1 billion-year-old rocks in [[Western Australia]].<ref name="AP-20151019">{{cite news |last=Borenstein |first=Seth |date=October 19, 2015 |title=Hints of life on what was thought to be desolate early Earth |url=https://apnews.com/e6be2537b4cd46ffb9c0585bae2b2e51 |url-status=live |work=[[Associated Press]] |archive-url=https://web.archive.org/web/20180712123134/https://apnews.com/e6be2537b4cd46ffb9c0585bae2b2e51 |archive-date=2018-07-12 |access-date=2020-02-17}}</ref><ref name="PNAS-20151124-pdf" />{{cite Injournal March|last1=Bell 2017|first1=Elizabeth A. |last2=Boehnke |first2=Patrick |last3=Harrison |first3=T. Mark |last4=Mao |first4=Wendy L. |display-authors=3 |date=November 24, putative2015 |title=Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon |url=https://www.pnas.org/content/pnas/early/2015/10/14/1517557112.full.pdf |url-status=live |journal=[[Proceedings of the National Academy of Sciences]] |volume=112 |issue=47 |pages=14518–14521 |bibcode=2015PNAS..11214518B |doi=10.1073/pnas.1517557112 |issn=0027-8424 |pmc=4664351 |pmid=26483481 |archive-url=https://web.archive.org/web/20200213002627/https://www.pnas.org/content/pnas/early/2015/10/14/1517557112.full.pdf |archive-date=2020-02-13 |access-date=2020-02-14 |doi-access=free}}</ref> There is further evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized [[microorganism]]s discovered in [[hydrothermal vent]] precipitates infrom the [[Nuvvuagittuq Greenstone Belt|Nuvvuagittuq Belt]] of [[Quebec]], [[Canada]], that may have lived as early as 4.28 billion years ago, not long after the [[Origin of water on Earth#History of water on Earth|oceans formed]] 4.4 billion years ago, and not long after the [[Age of Earth|formationEarth of the Earthformed]] 4.54 billion years ago.<ref name="NAT-20170301" /><ref name="NYT-20170301">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |date=March 1, 2017 |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 |department=Matter |url-status=live |newspaper=[[The New York Times]] |location=New York |issn=0362-4331 |archive-url=https://web.archive.org/web/20200104080331/https://www.nytimes.com/2017/03/01/science/earths-oldest-bacteria-fossils.html |archive-date=2020-01-04 |access-date=2017-03-02}} "A version of this article appears in print on March 2, 2017, Section A, Page 9 of the New York edition with the headline: Artful Squiggles in Rocks May Be Earth's Oldest Fossils."</ref> These earliest fossils, however, may have originated from non-biological processes.<ref name="Pearce 343–364" /><ref>{{cite journal |last1=Papineau |first1=Dominic |last2=De Gregorio |first2=Bradley T. |last3=Cody |first3=George D. |last4=O'Neil |first4=J. |last5=Steele |first5=A. |last6=Stroud |first6=R. M. |last7=Fogel |first7=M. L. |display-authors=3 |date=June 2011 |title=Young poorly crystalline graphite in the &gt;3.8-Gyr-old Nuvvuagittuq banded iron formation |journal=[[Nature Geoscience]] |volume=4 |issue=6 |pages=376–379 |bibcode=2011NatGe...4..376P |doi=10.1038/ngeo1155 |issn=1752-0894}}</ref><ref name="PNAS-20151124-pdf" /><ref>{{cite journal |last1=Nemchin |first1=Alexander A. |last2=Whitehouse |first2=Martin J. |last3=Menneken |first3=Martina |last4=Geisler |first4=Thorsten |last5=Pidgeon |first5=Robert T. |last6=Wilde |first6=Simon A. |display-authors=3 |date=July 3, 2008 |title=A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills |journal=[[Nature (journal)|Nature]] |volume=454 |issue=7200 |pages=92–95 |bibcode=2008Natur.454...92N |doi=10.1038/nature07102 |issn=0028-0836 |pmid=18596808 |s2cid=4415308}}</ref>▼
The similarities among all known present-day [[species]] indicate that they have diverged through the process of [[evolution]] from a [[common ancestor]].<ref>{{harvnb|Futuyma|2005}}</ref> Only a very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species, because "identifying every [[microorganism|microbial species]] on Earth presents a huge challenge."<ref name="NSF-2016002">{{cite press release |last1=Dybas |first1=Cheryl |last2=Fryling |first2=Kevin |date=May 2, 2016 |title=Researchers find that Earth may be home to 1 trillion species: Largest analysis of microbial data reveals that 99.999 percent of all species remain undiscovered |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=138446 |url-status=live |location=Alexandria, VA |publisher=[[National Science Foundation]] |id=News Release 16-052 |archive-url=https://web.archive.org/web/20160504111108/https://www.nsf.gov/news/news_summ.jsp?cntn_id=138446 |quote="Our results show that this leaves 100,000 times more microorganisms awaiting discovery -- and 100 million to be fully explored.<!--▼
"Microbial biodiversity, it appears, is greater than we ever imagined."-->|archive-date=2016-05-04 |access-date= 2016-12-11}}</ref><ref>{{cite journal |last1=Locey |first1=Kenneth J. |last2=Lennon |first2=Jay T. |date=May 24, 2016 |title=Scaling laws predict global microbial diversity |journal=[[Proceedings of the National Academy of Sciences of the United States of America|Proc. Natl. Acad. Sci. U.S.A.]] |volume=113 |issue=21 |pages=5970–5975 |doi=10.1073/pnas.1521291113 |issn=0027-8424 |pmc= 4889364 |pmid=27140646 |bibcode=2016PNAS..113.5970L |doi-access=free}}</ref> However, only 1.75–1.8 million have been named{{sfn|Chapman|2009}}<ref name="NYT-20141108-MJN">{{cite news |last=Novacek |first=Michael J. |date=November 8, 2014 |title=Prehistory's Brilliant Future |url=https://www.nytimes.com/2014/11/09/opinion/sunday/prehistorys-brilliant-future.html |url-status=live |department=[[Sunday Review]] |newspaper=[[The New York Times]] |location=New York |issn=0362-4331 |archive-url=https://web.archive.org/web/20141110003127/https://www.nytimes.com/2014/11/09/opinion/sunday/prehistorys-brilliant-future.html |archive-date=2014-11-10 |access-date=2014-12-25}} "A version of this article appears in print on November 9, 2014, Section SR, Page 6 of the New York edition with the headline: Prehistory's Brilliant Future."</ref> and 1.8 million documented in a central database.<ref name="col2016">{{cite web |url=http://www.catalogueoflife.org/annual-checklist/2019/info/ac |title=Catalogue of Life: 2019 Annual Checklist |year=2019 |publisher=[[Species 2000]]; [[Integrated Taxonomic Information System]] |access-date=2020-02-16 |archive-date=2020-10-07 |archive-url= https://web.archive.org/web/20201007184209/http://www.catalogueoflife.org/annual-checklist/2019/info/ac |url-status=live }}</ref> These currently living species represent less than one percent of all species that have ever lived on Earth.{{sfn|McKinney|1997|p=[https://books.google.com/books?id=4LHnCAAAQBAJ&pg=PA110 110]}}{{sfn|Stearns|Stearns|1999|p=[https://books.google.com/books?id=0BHeC-tXIB4C&q=99%20percent x]}}▼
{{Life timeline}}▼
▲The earliest evidence of life comes from [[biogenic substance|biogenic]] [[Δ13C|carbon signatures]]<ref name="Rosing 674–676"/><ref name="Ohtomo 25–28"/> and [[stromatolite]] fossils<ref>{{cite journal |last1=Nutman |first1=Allen P. |last2=Bennett |first2=Vickie C. |last3=Friend |first3=Clark R.L. |last4=Van Kranendonk |first4=Martin J. |last5=Chivas |first5=Allan R. |display-authors=3 |date=September 22, 2016 |title=Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures |url=https://ro.uow.edu.au/cgi/viewcontent.cgi?article=5181&context=smhpapers |url-status=live |format=PDF |journal=[[Nature (journal)|Nature]] |volume=537 |issue=7621 |pages=535–538 |bibcode=2016Natur.537..535N |s2cid=205250494 |doi=10.1038/nature19355 |issn=0028-0836 |pmid=27580034 |archive-url=https://web.archive.org/web/20200102053302/https://ro.uow.edu.au/cgi/viewcontent.cgi?article=5181&context=smhpapers |archive-date=2020-01-02 |access-date=2020-02-17}}</ref> discovered in 3.7 billion-year-old [[metasediment]]ary rocks from western [[Greenland]]. In 2015, possible "remains of [[biotic material|biotic life]]" were found in 4.1 billion-year-old rocks in [[Western Australia]].<ref name="AP-20151019">{{cite news |last=Borenstein |first=Seth |date=October 19, 2015 |title=Hints of life on what was thought to be desolate early Earth |url=https://apnews.com/e6be2537b4cd46ffb9c0585bae2b2e51 |url-status=live |work=[[Associated Press]] |archive-url=https://web.archive.org/web/20180712123134/https://apnews.com/e6be2537b4cd46ffb9c0585bae2b2e51 |archive-date=2018-07-12 |access-date=2020-02-17}}</ref><ref name="PNAS-20151124-pdf" /> In March 2017, putative evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized [[microorganism]]s discovered in [[hydrothermal vent]] precipitates in the [[Nuvvuagittuq Greenstone Belt|Nuvvuagittuq Belt]] of [[Quebec]], [[Canada]], that may have lived as early as 4.28 billion years ago, not long after the [[Origin of water on Earth#History of water on Earth|oceans formed]] 4.4 billion years ago, and not long after the [[Age of Earth|formation of the Earth]] 4.54 billion years ago.<ref name="NAT-20170301"/><ref name="NYT-20170301">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |date=March 1, 2017 |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 |department=Matter |url-status=live |newspaper=[[The New York Times]] |location=New York |issn=0362-4331 |archive-url=https://web.archive.org/web/20200104080331/https://www.nytimes.com/2017/03/01/science/earths-oldest-bacteria-fossils.html |archive-date=2020-01-04 |access-date=2017-03-02}} "A version of this article appears in print on March 2, 2017, Section A, Page 9 of the New York edition with the headline: Artful Squiggles in Rocks May Be Earth's Oldest Fossils."</ref>
 
[[Microbial mat]]s of coexisting [[bacteria]] and [[archaea]] were the dominant form of life in the early [[Archean]] eon, and many of the major steps in early evolution are thought to have taken place in this environment.<ref name="NisbetFowler1999">{{cite journal |last1=Nisbet |first1=Euan G. |last2=Fowler |first2=C.M.R. |author2-link=Mary Fowler (geologist) |date=December 7, 1999 |title=Archaean metabolic evolution of microbial mats |journal=[[Proceedings of the Royal Society#Proceedings of the Royal Society B|Proceedings of the Royal Society B]] |volume=266 |issue=1436 |pages=2375–2382 |doi=10.1098/rspb.1999.0934 |issn=0962-8452 |pmc=1690475}}</ref> The evolution of [[photosynthesis]] by [[cyanobacteria]], around 3.5 Ga, eventually led to a buildup of its waste product, [[oxygen]], in the oceanoceans. andAfter thenfree theoxygen atmosphere after depletingsaturated all available [[reductant]] substances on the [[Earth's surface]], it built up in the atmosphere, leading to the [[Great Oxygenation Event]], beginning around 2.4 Ga.<ref name="Anbar2007">{{cite journal |last1=Anbar |first1=Ariel D. |last2=Yun |first2=Duan |last3=Lyons |first3=Timothy W. |last4=Arnold |first4=Gail L. |last5=Kendall |first5=Brian |last6=Creaser |first6=Robert A. |last7=Kaufman |first7=Alan J. |last8=Gordon |first8=Gwyneth W. |last9=Scott |first9=Clinton |last10=Garvin |first10=Jessica |last11=Buick |first11=Roger |display-authors=3 |date=September 28, 2007 |title=A Whiff of Oxygen Before the Great Oxidation Event? |journal=[[Science (journal)|Science]] |volume=317 |issue=5846 |pages=1903–1906 |bibcode=2007Sci...317.1903A |doi=10.1126/science.1140325 |s2cid=25260892 |issn=0036-8075 |pmid=17901330}}</ref> The earliest evidence of [[eukaryote]]s (complex [[cell (biology)|cell]]s with [[organelle]]s) dates from 1.85 Ga,<ref>{{cite journal |last1=Knoll |first1=Andrew H. |author-link=Andrew H. Knoll |last2=Javaux |first2=Emmanuelle J. |last3=Hewitt |first3=David |last4=Cohen |first4=Phoebe |display-authors=3 |date=June 29, 2006 |title=Eukaryotic organisms in Proterozoic oceans |journal=[[Philosophical Transactions of the Royal Society B]] |volume=361 |issue=1470 |pages=1023–1038 |doi=10.1098/rstb.2006.1843 |issn=0962-8436 |pmc=1578724 |pmid=16754612}}</ref><ref name="Fedonkin2003" /> likely due to [[symbiogenesis]] between [[anaerobe|anaerobic]] archaea and [[aerobe|aerobic]] [[proteobacteria]] in co-adaptation against the new [[oxidative stress]]. While eukaryotes may have been present earlier, their diversification accelerated when aerobic [[cellular respiration]] by the [[endosymbiont]] [[mitochondria]] provided a more abundant source of [[biological energy]]. Later, aroundAround 1.6 Ga, some eukaryotes gained the ability to photosynthesize via endosymbiosis with cyanobacteria, and gave rise to various [[algae]] that eventually overtook cyanobacteria as the dominant [[primary producer]]s.
 
At around 1.7 Ga, [[multicellular organism]]s began to appear, with [[cellular differentiation|differentiated cell]]s performing specialised functions.<ref name="Bonner1999" /> [[SexualWhile reproduction]],early whichorganisms involves the fusion of male and female reproductive cells ([[gamete]]s) to create a [[zygote]] in a process called [[fertilization]] is, in contrast toreproduced [[asexual reproduction|asexually]], the primary method of reproduction for the vast majority of [[macroscopic]] organisms, including almost all [[eukaryotes]] (which includes [[animal]]s and [[plant]]s), is [[sexual reproduction]], the fusion of male and female reproductive cells ([[gamete]]s) to create a [[zygote]].<ref>{{cite journal |last1=Otto |first1=Sarah P. |author1-link=Sarah Otto |last2=Lenormand |first2=Thomas |date=April 1, 2002 |title=Resolving the paradox of sex and recombination |journal=[[Nature Reviews Genetics]] |volume=3 |issue=4 |pages=252–261 |doi=10.1038/nrg761 |s2cid=13502795 |issn=1471-0056 |pmid=11967550}}</ref> However theThe origin and [[evolution of sexual reproduction]] remain a puzzle for biologists, though it didis evolvethought fromto ahave commonevolved ancestor that wasfrom a single -celled eukaryotic speciesancestor.<ref name="Letunic I and Bork P">{{cite web |url=https://itol.embl.de/ |title=iTOL: Interactive Tree of Life |last1=Letunic |first1=Ivica |last2=Bork |first2=Peer |author2-link=Peer Bork |publisher=[[European Molecular Biology Laboratory]] |location=Heidelberg, Germany |access-date=2015-07-21 |archive-date=2022-06-10 |archive-url=https://web.archive.org/web/20220610171813/https://itol.embl.de/ |url-status=live }}
*{{cite journal |last1=Letunic |first1=Ivica |last2=Bork |first2=Peer |author2-link=Peer Bork |date=January 1, 2007 |title=Interactive Tree Of Life (iTOL): an online tool for phylogenetic tree display and annotation |url=https://itol.embl.de/help/17050570.pdf |journal=[[Bioinformatics (journal)|Bioinformatics]] |volume=23 |issue=1 |pages=127–128 |doi=10.1093/bioinformatics/btl529 |issn=1367-4803 |pmid=17050570 |access-date=2015-07-21 |doi-access=free |archive-date=2022-05-19 |archive-url=https://web.archive.org/web/20220519215247/https://itol.embl.de/help/17050570.pdf |url-status=live }}
*{{cite journal |last1=Letunic |first1=Ivica |last2=Bork |first2=Peer |author2-link=Peer Bork |date=July 1, 2011 |title=Interactive Tree Of Life v2: online annotation and display of phylogenetic trees made easy |url=https://itol.embl.de/help/gkr201.pdf |journal=[[Nucleic Acids Research]] |volume=39 |issue=Suppl. 2 |pages=W475–W478 |doi=10.1093/nar/gkr201 |issn=0305-1048 |pmc=3125724 |pmid=21470960 |access-date=2015-07-21 |archive-date=2021-11-01 |archive-url=https://web.archive.org/web/20211101090511/https://itol.embl.de/help/gkr201.pdf |url-status=live }}</ref> [[Bilateria]], animals having a left and a right side that are mirror images of each other, appeared by 555 Ma (million years ago).<ref>{{cite journal |last1=Fedonkin |first1=Mikhail A. |author1-link=Mikhail Fedonkin |last2=Simonetta |first2=Alberto |last3=Ivantsov |first3=Andrei Yu. |date=January 1, 2007 |title=New data on ''Kimberella'', the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications |url=https://www.monash.edu/__data/assets/pdf_file/0010/75673/fedonkin2.pdf |url-status=live |journal=Geological Society Special Publications |volume=286 |issue=1 |pages=157–179 |bibcode=2007GSLSP.286..157F |doi=10.1144/SP286.12 |s2cid=331187 |issn=0375-6440 |archive-url=https://web.archive.org/web/20170811081056/https://www.monash.edu/__data/assets/pdf_file/0010/75673/fedonkin2.pdf |archive-date=2017-08-11 |access-date=2020-02-18}}</ref>
 
TheWhile [[microorganism]]s formed the earliest [[terrestrial ecosystem]]s at least 2.7 Ga, the [[evolution of plants]] from freshwater [[green algae]] dateddates back even to about 1 billion years ago,.<ref>{{cite journal |last1=Strother |first1=Paul K. |last2=Battison |first2=Leila |last3=Brasier |first3=Martin D. |author3-link=Martin Brasier |last4=Wellman |first4=Charles H. |display-authors=3 |date=May 26, 2011 |title=Earth's earliest non-marine eukaryotes |journal=[[Nature (journal)|Nature]] |volume=473 |issue=7348 |pages=505–509 |bibcode=2011Natur.473..505S |doi=10.1038/nature09943 |s2cid=4418860 |issn=0028-0836 |pmid=21490597}}</ref> although evidence suggests that [[microorganism]]s formed the earliest [[terrestrial ecosystem]]s, at least 2.7 Ga.<ref>{{cite journal |last=Beraldi-Campesi |first=Hugo |date=February 23, 2013 |title=Early life on land and the first terrestrial ecosystems |journal=Ecological Processes |volume=2 |issue=1 |pages=1–17 |doi=10.1186/2192-1709-2-1 |doi-access=free |issn=2192-1709}}</ref> Microorganisms are thought to have paved the way for the inception of land plants in the [[Ordovician]] period. Land plants were so successful that they are thought to have contributed to the [[Late Devonian extinction|Late Devonian extinction event]].<ref name="AlgeoScheckler1998" /> (Theby longa causalcomplicated chain implied seems to involveprocess: (1) the success of early tree [[archaeopteris]] drew down CO<sub>2</sub> levels, leading to [[global cooling]] and lowered sea levels, (2) roots of archeopteris fostered soil development which ''increased'' rock weathering,; and (3) the subsequent nutrient run-off may have triggered [[algal bloom]]s resulting in [[anoxic event]]s which caused marine-life die-offs. Marineamong speciesmarine werespecies, the primary victims of the Late Devonian extinction.)
 
[[Bilateria]], animals having a left and a right side that are mirror images of each other, appeared by 555 Ma (million years ago).<ref>{{cite journal |last1=Fedonkin |first1=Mikhail A. |author1-link=Mikhail Fedonkin |last2=Simonetta |first2=Alberto |last3=Ivantsov |first3=Andrei Yu. |date=January 1, 2007 |title=New data on ''Kimberella'', the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications |url=https://www.monash.edu/__data/assets/pdf_file/0010/75673/fedonkin2.pdf |url-status=live |journal=Geological Society Special Publications |volume=286 |issue=1 |pages=157–179 |bibcode=2007GSLSP.286..157F |doi=10.1144/SP286.12 |issn=0375-6440 |s2cid=331187 |archive-url=https://web.archive.org/web/20170811081056/https://www.monash.edu/__data/assets/pdf_file/0010/75673/fedonkin2.pdf |archive-date=2017-08-11 |access-date=2020-02-18}}</ref> [[Ediacara biota]] appeared during the [[Ediacaran]] period,<ref>{{cite journal |last1=Jun-Yuan |first1=Chen |last2=Oliveri |first2=Paola |last3=Chia-Wei |first3=Li |author4=Gui-Qing Zhou |author5=Feng Gao |last6=Hagadorn |first6=James W. |last7=Peterson |first7=Kevin J. |last8=Davidson |first8=Eric H. |display-authors=3 |date=April 25, 2000 |title=Precambrian animal diversity: Putative phosphatized embryos from the Doushantuo Formation of China |journal=[[Proceedings of the National Academy of Sciences of the United States of America|Proc. Natl. Acad. Sci. U.S.A.]] |volume=97 |issue=9 |pages=4457–4462 |bibcode=2000PNAS...97.4457C |doi=10.1073/pnas.97.9.4457 |issn=0027-8424 |pmid=10781044 |pmc=18256 |doi-access=free}}</ref> while [[vertebrate]]s, along with most other modern [[phylum|phyla]] originated about {{ma|525|Ma|Cambrian}} during the [[Cambrian explosion]].<ref name="D-G.Shu et al. 1999">{{cite journal |last1=D-G. |first1=Shu |last2=H-L. |first2=Luo |last3=Conway Morris |first3=Simon |author3-link=Simon Conway Morris |author4=X-L. Zhang |author5=S-X. Hu |author6=L. Chen |author7=J. Han |author8=M. Zhu |author9=Y. Li |author10=L-Z. Chen |display-authors=3 |date=November 4, 1999 |title=Lower Cambrian vertebrates from south China |url=http://www.bios.niu.edu/davis/bios458/Shu1.pdf |journal=[[Nature (journal)|Nature]] |volume=402 |pages=42–46 |doi=10.1038/46965 |issue=6757 |bibcode=1999Natur.402...42S |s2cid=4402854 |issn=0028-0836 |archive-url=https://web.archive.org/web/20090226122732/http://www.bios.niu.edu/davis/bios458/Shu1.pdf |archive-date=2009-02-26 |access-date=2015-01-22}}</ref> During the [[Permian]] period, [[synapsid]]s, including the ancestors of [[mammal]]s, dominated the land,.<ref>{{cite web |url=http://www.csupomona.edu/~dfhoyt/classes/zoo138/SYNAPSID.HTML |title=Synapsid Reptiles |last=Hoyt |first=Donald F. |date=February 17, 1997 |website=ZOO 138 Vertebrate Zoology |publisher=[[California State Polytechnic University, Pomona]] |location=Pomona, CA |type=Lecture |archive-url=https://web.archive.org/web/20090520072737/http://www.csupomona.edu/~dfhoyt/classes/zoo138/SYNAPSID.HTML |archive-date=2009-05-20 |access-date=2015-01-22}}</ref> but

The most[[Permian–Triassic ofextinction thisevent]] groupkilled becamemost extinctcomplex inspecies theof [[Permian–Triassicits extinction event]]time, {{ma|252|Ma}}.<ref>{{cite web |url=https://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/ |url-status=live |title=The Great Dying |last=Barry |first=Patrick L. |date=January 28, 2002 |editor-last=Phillips |editor-first=Tony |work=Science@NASA |publisher=[[Marshall Space Flight Center]] |archive-url=https://web.archive.org/web/20100410015208/https://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/ |archive-date=2010-04-10 |access-date=2015-01-22}}</ref> During the recovery from this catastrophe, [[archosaur]]s became the most abundant land vertebrates;<ref name="TannerLucas2004">{{cite journal |last1=Tanner |first1=Lawrence H. |last2=Lucas |first2=Spencer G. |author2-link=Spencer G. Lucas |last3=Chapman |first3=Mary G. |date=March 2004 |title=Assessing the record and causes of Late Triassic extinctions |url=http://nmnaturalhistory.org/pdf_files/TJB.pdf |journal=[[Earth-Science Reviews]] |volume=65 |issue=1–2 |pages=103–139 |bibcode=2004ESRv...65..103T |doi=10.1016/S0012-8252(03)00082-5 |archive-url=https://web.archive.org/web/20071025225841/http://nmnaturalhistory.org/pdf_files/TJB.pdf |archive-date=2007-10-25 |access-date=2007-10-22}}</ref> one archosaur group, the [[dinosaur]]s, dominated the [[Jurassic]] and [[Cretaceous]] periods.<ref>{{harvnb|Benton|1997}}</ref> After the [[Cretaceous–Paleogene extinction event]] {{ma|Paleogene|Ma}} killed off the non-avian dinosaurs,<ref>{{cite journal |last1=Fastovsky |first1=David E. |last2=Sheehan |first2=Peter M. |date=March 2005 |title=The Extinction of the Dinosaurs in North America |url=https://www.geosociety.org/gsatoday/archive/15/3/pdf/i1052-5173-15-3-4.pdf |url-status=live |journal=[[Geological Society of America|GSA Today]] |volume=15 |issue=3 |pages=4–10 |doi=10.1130/1052-5173(2005)015<4:TEOTDI>2.0.CO;2 |issn=1052-5173 |archive-url=https://web.archive.org/web/20190322190338/https://www.geosociety.org/gsatoday/archive/15/3/pdf/i1052-5173-15-3-4.pdf |archive-date=2019-03-22 |access-date=2015-01-23}}</ref> mammals [[Adaptive radiation|increased rapidly in size and diversity]].<ref>{{cite news |last=Roach |first=John |date=June 20, 2007 |title=Dinosaur Extinction Spurred Rise of Modern Mammals |url=https://news.nationalgeographic.com/news/2007/06/070620-mammals-dinos.html |work=National Geographic News |location=Washington, D.C. |publisher=[[National Geographic Society]] |archive-url=https://web.archive.org/web/20080511161825/https://news.nationalgeographic.com/news/2007/06/070620-mammals-dinos.html |archive-date=2008-05-11 |access-date=2020-02-21}}
*{{cite journal |last1=Wible |first1=John R. |last2=Rougier |first2=Guillermo W. |last3=Novacek |first3=Michael J. |last4=Asher |first4=Robert J. |display-authors=3 |date=June 21, 2007 |title=Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary |journal=[[Nature (journal)|Nature]] |volume=447 |issue=7147 |pages=1003–1006 |bibcode=2007Natur.447.1003W |doi=10.1038/nature05854 |issn=0028-0836 |pmid=17581585 |s2cid=4334424}}</ref> Such [[Extinction event|mass extinction]]s may have accelerated evolution by providing opportunities for new groups of organisms to diversify.<ref name="Van Valkenburgh 1999 463–493">{{cite journal |last=Van Valkenburgh |first=Blaire |author-link=Blaire Van Valkenburgh |date=May 1, 1999 |title=Major Patterns in the History of Carnivorous Mammals |url=https://zenodo.org/record/890156 |journal=[[Annual Review of Earth and Planetary Sciences]] |volume=27 |pages=463–493 |bibcode=1999AREPS..27..463V |doi=10.1146/annurev.earth.27.1.463 |issn=1545-4495 |access-date=August 3, 2019 |archive-date=February 29, 2020 |archive-url=https://web.archive.org/web/20200229201201/https://zenodo.org/record/890156 |url-status=live }}</ref>
 
▲The similarities among all known present-day [[species]] indicate that they have diverged through the process of [[evolution]] from a [[common ancestor]].<ref>{{harvnb|Futuyma|2005}}</ref> Only a very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species, because "identifying every [[microorganism|microbial species]] on Earth presents a huge challenge."<ref name="NSF-2016002">{{cite press release |last1=Dybas |first1=Cheryl |last2=Fryling |first2=Kevin |date=May 2, 2016 |title=Researchers find that Earth may be home to 1 trillion species: Largest analysis of microbial data reveals that 99.999 percent of all species remain undiscovered |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=138446 |url-status=live |location=Alexandria, VA |publisher=[[National Science Foundation]] |id=News Release 16-052 |archive-url=https://web.archive.org/web/20160504111108/https://www.nsf.gov/news/news_summ.jsp?cntn_id=138446 |quote="Our results show that this leaves 100,000 times more microorganisms awaiting discovery -- and 100 million to be fully explored.<!--
▲"Microbial biodiversity, it appears, is greater than we ever imagined."--> |archive-date=2016-05-04 |access-date= 2016-12-11}}</ref><ref>{{cite journal |last1=Locey |first1=Kenneth J. |last2=Lennon |first2=Jay T. |date=May 24, 2016 |title=Scaling laws predict global microbial diversity |journal=[[Proceedings of the National Academy of Sciences of the United States of America|Proc. Natl. Acad. Sci. U.S.A.]] |volume=113 |issue=21 |pages=5970–5975 |bibcode=2016PNAS..113.5970L |doi=10.1073/pnas.1521291113 |issn=0027-8424 |pmc= 4889364 |pmid=27140646 |bibcode=2016PNAS..113.5970L |doi-access=free}}</ref> However, onlyOnly 1.75–1.8 million species have been named{{sfn|Chapman|2009}}<ref name="NYT-20141108-MJN">{{cite news |last=Novacek |first=Michael J. |date=November 8, 2014 |title=Prehistory's Brilliant Future |url=https://www.nytimes.com/2014/11/09/opinion/sunday/prehistorys-brilliant-future.html |url-status=live |department=[[Sunday Review]] |newspaper=[[The New York Times]] |location=New York |issn=0362-4331 |archive-url=https://web.archive.org/web/20141110003127/https://www.nytimes.com/2014/11/09/opinion/sunday/prehistorys-brilliant-future.html |archive-date=2014-11-10 |access-date=2014-12-25 |newspaper=[[The New York Times]] |department=[[Sunday Review]] |location=New York |issn=0362-4331}} "A version of this article appears in print on November 9, 2014, Section SR, Page 6 of the New York edition with the headline: Prehistory's Brilliant Future."</ref> and 1.8 million documented in a central database.<ref name="col2016">{{cite web |urlyear=http://www.catalogueoflife.org/annual-checklist/2019/info/ac |title=Catalogue of Life: 2019 Annual Checklist |yearurl=http://www.catalogueoflife.org/annual-checklist/2019/info/ac |publisher=[[Species 2000]]; [[Integrated Taxonomic Information System]] |accessurl-datestatus=2020-02-16 |archive-date=2020-10-07live |archive-url= https://web.archive.org/web/20201007184209/http://www.catalogueoflife.org/annual-checklist/2019/info/ac |urlarchive-statusdate=live2020-10-07 |access-date=2020-02-16 |publisher=[[Species 2000]]; [[Integrated Taxonomic Information System]]}}</ref> TheseThe currently living species represent less than one percent of all species that have ever lived on Earth.{{sfn|McKinney|1997|p=[https://books.google.com/books?id=4LHnCAAAQBAJ&pg=PA110 110]}}{{sfn|Stearns|Stearns|1999|p=[https://books.google.com/books?id=0BHeC-tXIB4C&q=99%20percent x]}}
 
▲{{Life timeline}}
 
== Earliest history of Earth ==
Retrieved from "https://en.wikipedia.org/wiki/History_of_life"