This timeline of the evolution of life outlines the major events in the development of life on the planet Earth (See Organism). For a thorough explanatory context, see the history of Earth, and geologic time scale. The dates given in this article are estimates based on scientific evidence.

In biology, evolution is the process by which populations of organisms acquire and pass on novel traits from generation to generation. Its occurrence over large stretches of time explains the origin of new species and ultimately the vast diversity of the biological world. Contemporary species are related to each other through common descent, products of evolution and speciation over billions of years.

Basic timeline

Axis scale: millions of years ago.

The basic timeline is a 4.5 billion year old Earth, with (very approximate) dates:

* 3.8 billion years of simple cells (prokaryotes),
* 3 billion years of photosynthesis,
* 2 billion years of complex cells (eukaryotes),
* 1 billion years of multicellular life,
* 600 million years of simple animals,
* 570 million years of arthropods (ancestors of insects, arachnids and crustaceans),
* 550 million years of complex animals,
* 500 million years of fish and proto-amphibians,
* 475 million years of land plants,
* 400 million years of insects and seeds,
* 360 million years of amphibians,
* 300 million years of reptiles,
* 200 million years of mammals,
* 150 million years of birds,
* 130 million years of flowers,
* 65 million years since the non-avian dinosaurs died out,
* 2.5 million years since the appearance of the genus Homo,
* 200,000 years since humans started looking like they do today,
* 25,000 years since Neanderthals died out.

Detailed timeline

Note that Ma, megaannum, means "million years ago".
Also note that Ka means "thousand years ago" and Ya means "years ago"

Hadean Eon

3800 Ma and earlier.
Date Event
4600 Ma The planet Earth forms from the accretion disc revolving around the young Sun.
4500 Ma According to one plausible theory, the planet Earth and the planet Theia collide, sending countless moonlets into orbit around the young Earth. These moonlets eventually coalesce to form the Moon.[1] The gravitational pull of the new Moon stabilises the Earth's fluctuating axis of rotation and sets up the conditions in which life formed[citation needed].
4100 Ma The surface of the Earth cools enough for the crust to solidify. The atmosphere and the oceans form.[2] PAH infall,[3] and Iron-Sulfide synthesis along deep ocean platelet boundaries, may have led to the RNA world of competing organic compounds.
Between 4500 and 3500 Ma The earliest life appears, possibly derived from self-reproducing RNA molecules.[4][5] The replication of these organisms requires resources like energy, space, and smaller building blocks, which soon become limited, resulting in competition, with natural selection favouring those molecules which are more efficient at replication. DNA molecules then take over as the main replicators and these archaic genomes soon develop inside enclosing membranes which provide a stable physical and chemical environment conducive to their replication: proto-cells.[6][7][8]
3900 Ma Late Heavy Bombardment: peak rate of impact events upon the inner planets by meteors. This constant disturbance may have obliterated any life that had evolved to that point, or possibly not, as some early microbes could have survived in hydrothermal vents below the Earth's surface;[9] or life might have been transported to Earth by a meteor.[10]
Somewhere between 3900 - 2500 Ma Cells resembling prokaryotes appear.[11] These first organisms are chemoautotrophs: they use carbon dioxide as a carbon source and oxidize inorganic materials to extract energy. Later, prokaryotes evolve glycolysis, a set of chemical reactions that free the energy of organic molecules such as glucose and store it in the chemical bonds of ATP. Glycolysis (and ATP) continue to be used in almost all organisms, unchanged, to this day.[12][13]

Archean Eon

3800 Ma – 2500 Ma
Date Event
3500 Ma Lifetime of the last universal ancestor;[14][15] the split between bacteria and archaea occurs.[16]

Bacteria develop primitive forms of photosynthesis which at first do not produce oxygen.[17] These organisms generate ATP by exploiting a proton gradient, a mechanism still used in virtually all organisms.
3000 Ma Photosynthesizing cyanobacteria evolve; they use water as a reducing agent, thereby producing oxygen as waste product.[18] The oxygen initially oxidizes dissolved iron in the oceans, creating iron ore. The oxygen concentration in the atmosphere subsequently rises, acting as a poison for many bacteria. The moon is still very close to the earth and causes tides 1,000 feet (305 m) high. The earth is continually wracked by hurricane force winds. These extreme mixing influences are thought to stimulate evolutionary processes. (See Oxygen catastrophe)

Proterozoic Eon

2500 Ma – 542 Ma
Date Event
By 1850 Ma Eukaryotic cells appear.[19][20] Eukaryotes contain membrane-bound organelles with diverse functions, probably derived from prokaryotes engulfing each other via phagocytosis. (See Endosymbiosis)
By 1200 Ma Sexual reproduction first appears, increasing the rate of evolution.[21]
1200 Ma Simple multicellular organisms evolve, mostly consisting of cell colonies of limited complexity.
850–630 Ma A global glaciation may have occurred.[22][23] Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution.[24][25][26]
580–542 Ma The Ediacaran biota represent the first large, complex multicellular organisms - although their affinities remain a subject of debate.[27]
580–500 Ma Most modern phyla of animals begin to appear in the fossil record during the Cambrian explosion.[28][29]
580–540 Ma The accumulation of atmospheric oxygen allows the formation of an ozone layer.[30] This blocks ultraviolet radiation, permitting the colonisation of the land.[30]
560 Ma Earliest fungi

Phanerozoic Eon

542 Ma – present

The Phanerozoic Eon, literally the "period of well-displayed life", marks the appearance in the fossil record of abundant, shell-forming and/or trace-making organisms. It is subdivided into three eras, the Paleozoic, Mesozoic and Cenozoic, which are divided by major mass extinctions.

Paleozoic Era

542 Ma – 251.0 Ma
Date Event
535 Ma Major diversification of living things in the oceans: chordates, arthropods (e.g. trilobites, crustaceans), echinoderms, mollusks, brachiopods, foraminifers and radiolarians, etc.
530 Ma The first known footprints on land date to 530 Ma, indicating that early animal explorations may have predated the development of terrestrial plants.[31]
525 Ma Earliest graptolites.
510 Ma First cephalopods (Nautiloids) and chitons.
505 Ma Fossilization of the Burgess Shale.
485 Ma First vertebrates with true bones (jawless fishes).
450 Ma Land arthropod burrows (millipedes) appear, along with the first complete conodonts and echinoids.
440 Ma First agnathan fishes: Heterostraci, Galeaspida, and Pituriaspida.
434 Ma The first primitive plants move onto land,[32][citation needed] having evolved from green algae living along the edges of lakes.[33] They are accompanied by fungi, which may have aided the colonisation of land through symbiosis.
420 Ma Earliest ray-finned fishes, trigonotarbid arachnids, and land scorpions.
410 Ma First signs of teeth in fish. Earliest nautiid nautiloids, lycophytes, and trimerophytes.
395 Ma First lichens, stoneworts. Earliest harvestman, mites, hexapods (springtails), and ammonoids.
363 Ma By the start of the Carboniferous Period, the Earth begins to be recognisable. Insects roamed the land and would soon take to the skies; sharks swam the oceans as top predators,[34] and vegetation covered the land, with seed-bearing plants and forests soon to flourish.

Four-limbed tetrapods gradually gain adaptations which will help them occupy a terrestrial life-habit.
360 Ma First crabs and ferns. Land flora dominated by seed ferns.
350 Ma First large sharks, ratfishes, and hagfish.
340 Ma Diversification of amphibians.
330 Ma First amniote vertebrates (Paleothyris).
305 Ma Earliest diapsid reptiles (e.g. Petrolacosaurus).
280 Ma Earliest beetles, seed plants and conifers diversify while lepidodendrids and sphenopsids decrease. Terrestrial temnospondyl amphibians and pelycosaurs (e.g. Dimetrodon) diversify in species.
251.4 Ma The Permian-Triassic extinction event eliminates over 90-95% of marine species. Terrestrial organisms were not as seriously affected as the marine biota. This "clearing of the slate" may have led to an ensuing diversification, but life on land took 30M years to completely recover.[35]
[edit] Mesozoic Era
Date Event
From 251.4 Ma The Mesozoic Marine Revolution begins: increasingly well-adapted and diverse predators pressurise sessile marine groups; the "balance of power" in the oceans shifts dramatically as some groups of prey adapt more rapidly and effectively than others.
245 Ma Earliest ichthyosaurs.
240 Ma Increase in diversity of gomphodont cynodonts and rhynchosaurs.
225 Ma Earliest dinosaurs (prosauropods), first cardiid bivalves, diversity in cycads, bennettitaleans, and conifers. First teleost fishes.
215 Ma First mammals (e.g. Eozostrodon), minor vertebrate extinctions occur
220 Ma
Eoraptor, among the earliest dinosaurs, appeared in the fossil record 230 million years ago.

Gymnosperm forests dominate the land; herbivores grow to huge sizes in order to accommodate the large guts necessary to digest the nutrient-poor plants.[citation needed], first flies and turtles (Odontochelys). First Coelophysoid dinosaurs
200 Ma The first accepted evidence for viruses (at least, the group Geminiviridae) exists.[36] Viruses are still poorly understood and may have arisen before "life" itself, or may be a more recent phenomenon.

Major extinctions in terrestrial vertebrates and large amphibians. Earliest examples of Ankylosaurian dinosaurs
195 Ma First pterosaurs with specialized feeding (Dorygnathus). First sauropod dinosaurs. Diversification in small, ornithischian dinosaurs: heterodontosaurids, fabrosaurids, and scelidosaurids.
190 Ma Pliosaurs appear in the fossil record. First lepidopteran insects (Archaeolepis), hermit crabs, modern starfish, irregular echinoids, corbulid bivalves, and tubulipore bryozoans. Extensive development of sponge reefs.
176 Ma First members of the Stegosauria group of dinosaurs
170 Ma Earliest salamanders, newts, cryptoclidid & elasmosaurid plesiosaurs, and cladotherian mammals. Cynodonts become extinct while sauropod dinosaurs diversify.
165 Ma First rays and glycymeridid bivalves.
161 Ma Ceratopsian dinosaurs appear in the fossil record (Yinlong)
155 Ma First blood-sucking insects (ceratopogonids), rudist bivalves, and cheilosome bryozoans. Archaeopteryx, a possible ancestor to the birds, appears in the fossil record, along with triconodontid and symmetrodont mammals. Diversity in stegosaurian and theropod dinosaurs.
130 Ma The rise of the Angiosperms: These flowering plants boast structures that attract insects and other animals to spread pollen. This innovation causes a major burst of animal evolution through co-evolution. First freshwater pelomedusid turtles.
115 Ma First monotreme mammals.
110 Ma First hesperornithes, toothed diving birds. Earliest limopsid, verticordiid, and thyasirid bivalves.
106 Ma Spinosaurus, the largest theropod dinosaur, appears in the fossil record.
100 Ma Earliest bees.
90 Ma Extinction of ichthyosaurs. Earliest snakes and nuculanid bivalves. Large diversification in angiosperms: magnoliids, rosids, hamamelidids, monocots, and ginger. Earliest examples of ticks.
80 Ma First ants and termites.
70 Ma Multituberculate mammals increase in diversity. First yoldiid bivalves.
68 Ma Tyrannosaurus, the largest terrestrial predator of North America appears in the fossil record. First species of Triceratops.
[edit] Cenozoic Era

65.5 Ma – present
Date Event
65.5 Ma The Cretaceous–Tertiary extinction event eradicates about half of all animal species, including mosasaurs, pterosaurs, plesiosaurs, ammonites, belemnites, rudist and inoceramid bivalves, most planktic foraminifers, and all of the dinosaurs excluding their descendants the birds [37]
From 65 Ma Rapid dominance of conifers and ginkgos in high latitudes, along with mammals becoming the dominant species. First psammobiid bivalves. Rapid diversification in ants.
63 Ma Evolution of the creodonts, an important group of carnivorous mammals.
60 Ma Diversification of large, flightless birds. Earliest true primates, along with the first semelid bivalves, edentates, carnivorous and lipotyphlan mammals, and owls. The ancestors of the carnivorous mammals (miacids) were alive.
56 Ma Gastornis, a large, flightless bird appears in the fossil record, becoming an apex predator at the time.
55 Ma Modern bird groups diversify (first song birds, parrots, loons, swifts, woodpeckers), first whale (Himalayacetus), earliest rodents, lagomorphs, armadillos, appearance of sirenians, proboscideans, perissodactyl and artiodactyl mammals in the fossil record. Angiosperms diversify. The ancestor (according to theory) of the species in Carcharodon, the early mako shark Isurus hastalis, is alive.
52 Ma First bats appear (Onychonycteris).
50 Ma Peak diversity of dinoflagellates and nanofossils, increase in diversity of anomalodesmatan and heteroconch bivalves, brontotheres, tapirs, rhinoceroses, and camels appear in the fossil record, diversification of primates.
40 Ma Modern type butterflies and moths appear. Extinction of Gastornis. Basilosaurus, one of the first of the giant whales, appeared in the fossil record.
37 Ma First Nimravid carnivores ("False Saber-toothed Cats") - these species are unrelated to modern-type felines
35 Ma Grasses evolve from among the angiosperms; grasslands begin to expand. Slight increase in diversity of cold-tolerant ostracods and foraminifers, along with major extinctions of gastropods, reptiles, and amphibians. Many modern mammal groups begin to appear: first glyptodonts, ground sloths, dogs, peccaries, and the first eagles and hawks. Diversity in toothed and baleen whales.
33 Ma Evolution of the thylacinid marsupials (Badjcinus).
30 Ma First balanids and eucalypts, extinction of embrithopod and brontothere mammals, earliest pigs and cats.
28 Ma Paraceratherium appears in the fossil record, the largest terrestrial mammal that ever lived.
25 Ma First deer.
20 Ma First giraffes and giant anteaters, increase in bird diversity.
15 Ma Mammut appears in the fossil record, first bovids and kangaroos, diversity in Australian megafauna.
10 Ma Grasslands and savannas are established, diversity in insects, especially ants and termites, horses increase in body size and develop high-crowned teeth, major diversification in grassland mammals and snakes.
6.5 Ma First hominin (Sahelanthropus).
6 Ma Australopithecines diversify (Orrorin, Ardipithecus)
5 Ma First tree sloths and hippopotami, diversification of grazing herbivores, large carnivorous mammals, burrowing rodents, kangaroos, birds, and small carnivores, vultures increase in size, decrease in the number of perissodactyl mammals. Extinction of Nimravid carnivores
4.8 Ma Mammoths appear in the fossil record.
4 Ma Evolution of Australopithecus, Stupendemys appears in the fossil record as the largest freshwater turtle.
3 Ma The Great American Interchange, where various land and freshwater faunas migrated between North and South America. Armadillos, opossums, hummingbirds, and vampire bats traveled to North America while horses, tapirs, saber-toothed cats, and deer entered South America. The first short-faced bears (Arctodus) appear.
2.7 Ma Evolution of Paranthropus
2.5 Ma The earliest species of Smilodon evolve
2 Ma First members of the genus Homo appear in the fossil record. Diversification of conifers in high latitudes. The eventual ancestor of cattle, Bos primigenius evolves in India
1.7 Ma Extinction of australopithecines.
1.2 Ma Evolution of Homo antecessor. The last members of Paranthropus die out.
600 ka Evolution of Homo heidelbergensis
350 ka Evolution of Neanderthals
300 ka Gigantopithecus, a giant relative of the orangutan dies out from Asia
200 ka Anatomically modern humans appear in Africa.[38][39][40] Around 50,000 years before present they start colonising the other continents, replacing the Neanderthals in Europe and other hominins in Asia.
40 ka The last of the giant monitor lizards (Megalania) die out
30 ka Extinction of Neanderthals
15 ka The last Woolly rhinoceros (Coelodonta) are believed to have gone extinct
11 ka The giant short-faced bears (Arctodus) vanish from North America, with the last Giant Ground Sloths dying out. All Equidae become extinct in North America
10 ka The Holocene Epoch starts 10,000[41] years ago after the Late Glacial Maximum. The last mainland species of Woolly mammoth (Mammuthus primigenius) die out, as does the last Smilodon species
6 ka Small populations of American Mastodon die off in places like Utah and Michigan
4500 ya The last members of a dwarf race of Woolly Mammoths vanish from Wrangel Island near Alaska
383 ya The last wild Aurochs die out
37 ya The Thylacine goes extinct in a Tasmanian zoo, the last member of the family Thylacinidae
Present day The impact of humanity is felt in all corners of the globe and contributing to a dramatically rising extinction rate, estimated in 1995 to be 100 times the background rate.[42][43]

See also

Further reading

* The Ancestor's Tale by Richard Dawkins, for a list of ancestors common to humans and other living species

References

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3. ^ *The 'PAH World'
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28. ^ The Cambrian Period
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30. ^ a b Formation of the Ozone Layer
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External links

* Berkeley Evolution
* Tree of Life Web Project - explore complete phylogenetic tree interactively
* A more compact timeline at the TalkOrigins Archive
* Palaeos - The Trace of Life on Earth
* University of Waikato - Sequence of Plant Evolution
* University of Waikato - Sequence of Animal Evolution
* Graphical Timeline of evolution
* History of Life on Earth
* Exploring Time from Planck Time to the lifespan of the universe
* Interactive Plant Evolution Timeline - from the University of Cambridge Ensemble Project