History of life

The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga.[1][2][3] The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor.[4]

The earliest clear evidence of life comes from biogenic carbon signatures[2][3] and stromatolite fossils[5] discovered in 3.7 billion-year-old metasedimentary rocks from western Greenland. In 2015, possible "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.[6][7] There is further evidence of possibly the oldest forms of life in the form of fossilized microorganisms in hydrothermal vent precipitates from the Nuvvuagittuq Belt, that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, and after the Earth formed 4.54 billion years ago.[8][9] These earliest fossils, however, may have originated from non-biological processes.[1][10][7][11]

Microbial mats 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.[12] The evolution of photosynthesis by cyanobacteria, around 3.5 Ga, eventually led to a buildup of its waste product, oxygen, in the oceans. After free oxygen saturated all available reductant substances on the Earth's surface, it built up in the atmosphere, leading to the Great Oxygenation Event around 2.4 Ga.[13] The earliest evidence of eukaryotes (complex cells with organelles) dates from 1.85 Ga,[14][15] likely due to symbiogenesis between anaerobic archaea and 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. Around 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 producers.

At around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions.[16] While early organisms reproduced asexually, the primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes (which includes animals and plants), is sexual reproduction, the fusion of male and female reproductive cells (gametes) to create a zygote.[17] The origin and evolution of sexual reproduction remain a puzzle for biologists, though it is thought to have evolved from a single-celled eukaryotic ancestor.[18]

While microorganisms formed the earliest terrestrial ecosystems at least 2.7 Ga, the evolution of plants from freshwater green algae dates back to about 1 billion years ago.[19][20] 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 event[21] as early tree Archaeopteris drew down CO2 levels, leading to global cooling and lowered sea levels, while their roots increased rock weathering and nutrient run-offs which may have triggered algal bloom anoxic events.

Bilateria, animals having a left and a right side that are mirror images of each other, appeared by 555 Ma (million years ago).[22] Ediacara biota appeared during the Ediacaran period,[23] while vertebrates, along with most other modern phyla originated about 525 Ma during the Cambrian explosion.[24] During the Permian period, synapsids, including the ancestors of mammals, dominated the land.[25]

The Permian–Triassic extinction event killed most complex species of its time, 252 Ma.[26] During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates;[27] one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods.[28] After the Cretaceous–Paleogene extinction event 66 Ma killed off the non-avian dinosaurs,[29] mammals increased rapidly in size and diversity.[30] Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.[31]

Only a very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species, because "identifying every microbial species on Earth presents a huge challenge."[32][33] Only 1.75–1.8 million species have been named[34][35] and 1.8 million documented in a central database.[36] The currently living species represent less than one percent of all species that have ever lived on Earth.[37][38]


  1. ^ a b Pearce, Ben K.D.; Tupper, Andrew S.; Pudritz, Ralph E.; et al. (March 1, 2018). "Constraining the Time Interval for the Origin of Life on Earth". Astrobiology. 18 (3): 343–364. arXiv:1808.09460. Bibcode:2018AsBio..18..343P. doi:10.1089/ast.2017.1674. ISSN 1531-1074. PMID 29570409. S2CID 4419671.
  2. ^ a b Rosing, Minik T. (January 29, 1999). "13C-Depleted Carbon Microparticles in >3700-Ma Sea-Floor Sedimentary Rocks from West Greenland". Science. 283 (5402): 674–676. Bibcode:1999Sci...283..674R. doi:10.1126/science.283.5402.674. ISSN 0036-8075. PMID 9924024.
  3. ^ a b Ohtomo, Yoko; Kakegawa, Takeshi; Ishida, Akizumi; et al. (January 2014). "Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks". Nature Geoscience. 7 (1): 25–28. Bibcode:2014NatGe...7...25O. doi:10.1038/ngeo2025. ISSN 1752-0894.
  4. ^ Futuyma 2005
  5. ^ Nutman, Allen P.; Bennett, Vickie C.; Friend, Clark R.L.; et al. (September 22, 2016). "Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures" (PDF). Nature. 537 (7621): 535–538. Bibcode:2016Natur.537..535N. doi:10.1038/nature19355. ISSN 0028-0836. PMID 27580034. S2CID 205250494. Archived from the original on 2020-01-02. Retrieved 2020-02-17.
  6. ^ Borenstein, Seth (October 19, 2015). "Hints of life on what was thought to be desolate early Earth". Associated Press. Archived from the original on 2018-07-12. Retrieved 2020-02-17.
  7. ^ a b Bell, Elizabeth A.; Boehnke, Patrick; Harrison, T. Mark; et al. (November 24, 2015). "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon" (PDF). Proceedings of the National Academy of Sciences. 112 (47): 14518–14521. Bibcode:2015PNAS..11214518B. doi:10.1073/pnas.1517557112. ISSN 0027-8424. PMC 4664351. PMID 26483481. Archived (PDF) from the original on 2020-02-13. Retrieved 2020-02-14.
  8. ^ Cite error: The named reference NAT-20170301 was invoked but never defined (see the help page).
  9. ^ Zimmer, Carl (March 1, 2017). "Scientists Say Canadian Bacteria Fossils May Be Earth's Oldest". Matter. The New York Times. New York. ISSN 0362-4331. Archived from the original on 2020-01-04. Retrieved 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."
  10. ^ Papineau, Dominic; De Gregorio, Bradley T.; Cody, George D.; et al. (June 2011). "Young poorly crystalline graphite in the >3.8-Gyr-old Nuvvuagittuq banded iron formation". Nature Geoscience. 4 (6): 376–379. Bibcode:2011NatGe...4..376P. doi:10.1038/ngeo1155. ISSN 1752-0894.
  11. ^ Nemchin, Alexander A.; Whitehouse, Martin J.; Menneken, Martina; et al. (July 3, 2008). "A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills". Nature. 454 (7200): 92–95. Bibcode:2008Natur.454...92N. doi:10.1038/nature07102. ISSN 0028-0836. PMID 18596808. S2CID 4415308.
  12. ^ Nisbet, Euan G.; Fowler, C.M.R. (December 7, 1999). "Archaean metabolic evolution of microbial mats". Proceedings of the Royal Society B. 266 (1436): 2375–2382. doi:10.1098/rspb.1999.0934. ISSN 0962-8452. PMC 1690475.
  13. ^ Anbar, Ariel D.; Yun, Duan; Lyons, Timothy W.; et al. (September 28, 2007). "A Whiff of Oxygen Before the Great Oxidation Event?". Science. 317 (5846): 1903–1906. Bibcode:2007Sci...317.1903A. doi:10.1126/science.1140325. ISSN 0036-8075. PMID 17901330. S2CID 25260892.
  14. ^ Knoll, Andrew H.; Javaux, Emmanuelle J.; Hewitt, David; et al. (June 29, 2006). "Eukaryotic organisms in Proterozoic oceans". Philosophical Transactions of the Royal Society B. 361 (1470): 1023–1038. doi:10.1098/rstb.2006.1843. ISSN 0962-8436. PMC 1578724. PMID 16754612.
  15. ^ Cite error: The named reference Fedonkin2003 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Bonner1999 was invoked but never defined (see the help page).
  17. ^ Otto, Sarah P.; Lenormand, Thomas (April 1, 2002). "Resolving the paradox of sex and recombination". Nature Reviews Genetics. 3 (4): 252–261. doi:10.1038/nrg761. ISSN 1471-0056. PMID 11967550. S2CID 13502795.
  18. ^ Letunic, Ivica; Bork, Peer. "iTOL: Interactive Tree of Life". Heidelberg, Germany: European Molecular Biology Laboratory. Archived from the original on 2022-06-10. Retrieved 2015-07-21.
  19. ^ Strother, Paul K.; Battison, Leila; Brasier, Martin D.; et al. (May 26, 2011). "Earth's earliest non-marine eukaryotes". Nature. 473 (7348): 505–509. Bibcode:2011Natur.473..505S. doi:10.1038/nature09943. ISSN 0028-0836. PMID 21490597. S2CID 4418860.
  20. ^ Beraldi-Campesi, Hugo (February 23, 2013). "Early life on land and the first terrestrial ecosystems". Ecological Processes. 2 (1): 1–17. Bibcode:2013EcoPr...2....1B. doi:10.1186/2192-1709-2-1. ISSN 2192-1709.
  21. ^ Cite error: The named reference AlgeoScheckler1998 was invoked but never defined (see the help page).
  22. ^ Fedonkin, Mikhail A.; Simonetta, Alberto; Ivantsov, Andrei Yu. (January 1, 2007). "New data on Kimberella, the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications" (PDF). Geological Society Special Publications. 286 (1): 157–179. Bibcode:2007GSLSP.286..157F. doi:10.1144/SP286.12. ISSN 0375-6440. S2CID 331187. Archived (PDF) from the original on 2017-08-11. Retrieved 2020-02-18.
  23. ^ Jun-Yuan, Chen; Oliveri, Paola; Chia-Wei, Li; et al. (April 25, 2000). "Precambrian animal diversity: Putative phosphatized embryos from the Doushantuo Formation of China". Proc. Natl. Acad. Sci. U.S.A. 97 (9): 4457–4462. Bibcode:2000PNAS...97.4457C. doi:10.1073/pnas.97.9.4457. ISSN 0027-8424. PMC 18256. PMID 10781044.
  24. ^ D-G., Shu; H-L., Luo; Conway Morris, Simon; et al. (November 4, 1999). "Lower Cambrian vertebrates from south China" (PDF). Nature. 402 (6757): 42–46. Bibcode:1999Natur.402...42S. doi:10.1038/46965. ISSN 0028-0836. S2CID 4402854. Archived from the original (PDF) on 2009-02-26. Retrieved 2015-01-22.
  25. ^ Hoyt, Donald F. (February 17, 1997). "Synapsid Reptiles". ZOO 138 Vertebrate Zoology (Lecture). Pomona, CA: California State Polytechnic University, Pomona. Archived from the original on 2009-05-20. Retrieved 2015-01-22.
  26. ^ Barry, Patrick L. (January 28, 2002). Phillips, Tony (ed.). "The Great Dying". Science@NASA. Marshall Space Flight Center. Archived from the original on 2010-04-10. Retrieved 2015-01-22.
  27. ^ Tanner, Lawrence H.; Lucas, Spencer G.; Chapman, Mary G. (March 2004). "Assessing the record and causes of Late Triassic extinctions" (PDF). Earth-Science Reviews. 65 (1–2): 103–139. Bibcode:2004ESRv...65..103T. doi:10.1016/S0012-8252(03)00082-5. Archived from the original (PDF) on 2007-10-25. Retrieved 2007-10-22.
  28. ^ Benton 1997
  29. ^ Fastovsky, David E.; Sheehan, Peter M. (March 2005). "The Extinction of the Dinosaurs in North America" (PDF). GSA Today. 15 (3): 4–10. doi:10.1130/1052-5173(2005)015<4:TEOTDI>2.0.CO;2. ISSN 1052-5173. Archived (PDF) from the original on 2019-03-22. Retrieved 2015-01-23.
  30. ^ Roach, John (June 20, 2007). "Dinosaur Extinction Spurred Rise of Modern Mammals". National Geographic News. Washington, D.C.: National Geographic Society. Archived from the original on 2008-05-11. Retrieved 2020-02-21.
  31. ^ Van Valkenburgh, Blaire (May 1, 1999). "Major Patterns in the History of Carnivorous Mammals". Annual Review of Earth and Planetary Sciences. 27: 463–493. Bibcode:1999AREPS..27..463V. doi:10.1146/annurev.earth.27.1.463. ISSN 1545-4495. Archived from the original on February 29, 2020. Retrieved August 3, 2019.
  32. ^ Dybas, Cheryl; Fryling, Kevin (May 2, 2016). "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" (Press release). Alexandria, VA: National Science Foundation. News Release 16-052. Archived from the original on 2016-05-04. Retrieved 2016-12-11. "Our results show that this leaves 100,000 times more microorganisms awaiting discovery -- and 100 million to be fully explored.
  33. ^ Locey, Kenneth J.; Lennon, Jay T. (May 24, 2016). "Scaling laws predict global microbial diversity". Proc. Natl. Acad. Sci. U.S.A. 113 (21): 5970–5975. Bibcode:2016PNAS..113.5970L. doi:10.1073/pnas.1521291113. ISSN 0027-8424. PMC 4889364. PMID 27140646.
  34. ^ Chapman 2009.
  35. ^ Novacek, Michael J. (November 8, 2014). "Prehistory's Brilliant Future". Sunday Review. The New York Times. New York. ISSN 0362-4331. Archived from the original on 2014-11-10. Retrieved 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."
  36. ^ "Catalogue of Life: 2019 Annual Checklist". Species 2000; Integrated Taxonomic Information System. 2019. Archived from the original on 2020-10-07. Retrieved 2020-02-16.
  37. ^ McKinney 1997, p. 110.
  38. ^ Stearns & Stearns 1999, p. x.