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Thetimeline of life represents the currentscientific theory outlining the major events during the development oflife onEarth. Dates in this article are consensus estimates based onscientific evidence, mainlyfossils.
Inbiology,evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level ofbiological organization, fromkingdoms tospecies, and individualorganisms andmolecules, such asDNA andproteins. The similarities between all present day organisms imply acommon ancestor from which all known species, living andextinct, have diverged. More than 99 percent of all species that ever lived (over five billion)[1] are estimated to beextinct.[2][3] Estimates on the number of Earth's current species range from 10 million to 14 million,[4] with about 1.2 million or 14% documented, the restnot yet described.[5] However, a 2016 report estimates an additional 1 trillion microbial species, with only 0.001% described.[6]
There has been controversy between more traditional views of steadily increasingbiodiversity, and a newer view of cycles of annihilation and diversification, so that certain past times, such as theCambrian explosion, experienced maximums of diversity followed by sharp winnowing.[7][8]
Species go extinct constantly as environments change, as organisms compete for environmental niches, and as genetic mutation leads to the rise of new species from older ones. At long irregular intervals, Earth's biosphere suffers a catastrophic die-off, amass extinction,[9] often comprising an accumulation of smaller extinction events over a relatively brief period.[10]
The first known mass extinction was theGreat Oxidation Event 2.4 billion years ago, which killed most of the planet'sobligate anaerobes. Researchers have identified five other major extinction events in Earth's history, with estimated losses below:[11]
Smaller extinction events have occurred in the periods between, with some dividinggeologic time periods and epochs. TheHolocene extinction event is currently under way.[13]
Factors in mass extinctions includecontinental drift, changes in atmospheric and marinechemistry,volcanism and other aspects ofmountain formation, changes inglaciation, changes insea level, andimpact events.[10]
In this timeline,Ma (formegaannum) means "million years ago,"ka (forkiloannum) means "thousand years ago," andya means "years ago."
4540 Ma – 4031 Ma
| Date | Event |
|---|---|
| 4540 Ma | Planet Earth forms from theaccretion disc revolving around the youngSun, perhaps preceded by formation oforganic compounds necessary for life in the surroundingprotoplanetary disk ofcosmic dust.[14][15] |
| 4510 Ma | According to thegiant-impact hypothesis, theMoon originated when Earth and the hypothesized planetTheia collided, sending into orbit myriad moonlets which eventually coalesced into our single Moon.[16][17] The Moon's gravitational pullstabilised Earth's fluctuatingaxis of rotation, setting up regular climatic conditions favoringabiogenesis.[18] |
| 4404 Ma | Evidence of thefirst liquid water on Earth which were found in the oldest knownzircon crystals.[19] |
| 4280–3770 Ma | Earliest possible appearance of life on Earth.[20][21][22][23] |
4031 Ma – 2500 Ma
| Date | Event |
|---|---|
| 4100 Ma | Earliest possible preservation of biogenic carbon.[24][25] |
| 4100–3800 Ma | Late Heavy Bombardment (LHB): extended barrage by meteoroidsimpacting the inner planets. Thermal flux from widespreadhydrothermal activity during the LHB may have aided abiogenesis and life's early diversification.[26] Possible remains ofbiotic life were found in 4.1 billion-year-old rocks inWestern Australia.[27][28] |
| 4000 Ma | Formation of agreenstone belt of theAcasta Gneiss of theSlave craton in northwest Canada - the oldest known rock belt.[29] |
| 3900–2500 Ma | Cells resemblingprokaryotes appear.[30] These first organisms are believed to have beenchemoautotrophs, usingcarbon dioxide as acarbon source andoxidizing inorganic materials to extract energy. |
| 3800 Ma | Formation of a greenstone belt of theIsua complex in westernGreenland, whose isotope frequencies suggest the presence of life.[29] The earliest evidence for life on Earth includes: 3.8 billion-year-oldbiogenichematite in abanded iron formation of theNuvvuagittuq Greenstone Belt in Canada;[31]graphite in 3.7 billion-year-old metasedimentary rocks in western Greenland;[32] andmicrobial matfossils in 3.48 billion-year-oldsandstone inWestern Australia.[33][34] |
| 3800–3500 Ma | Last universal common ancestor (LUCA):[35][36] split betweenbacteria andarchaea.[37] Bacteria develop primitivephotosynthesis, which at first did not produceoxygen.[38] These organisms exploit aproton gradient to generateadenosine triphosphate (ATP), a mechanism used by virtually all subsequent organisms.[39][40][41] |
| 3000 Ma | Photosynthesizingcyanobacteria using water as areducing agent and producing oxygen as a waste product.[42] Free oxygen initially oxidizes dissolved iron in the oceans, creatingiron ore. Oxygen concentration in the atmosphere slowly rises,poisoning many bacteria and eventually triggering theGreat Oxygenation Event. |
| 2800 Ma | Oldest evidence for microbial life on land in the form of organic matter-richpaleosols,ephemeral ponds andalluvial sequences, some bearingmicrofossils.[43] |
2500 Ma – 539 Ma. Contains thePalaeoproterozoic,Mesoproterozoic andNeoproterozoic eras.
| Date | Event |
|---|---|
| 2500 Ma | Great Oxidation Event led by cyanobacteria's oxygenic photosynthesis.[42] Commencement ofplate tectonics with old marine crust dense enough tosubduct.[29] |
| 2400 Ma | Possible landfungi evidence from molecules. |
| 2023 Ma | Formation of theVredefort impact structure, one of the largest and oldest verified impact structures on Earth. The crater is estimated to have been between 170–300 kilometres (110–190 mi) across when it first formed.[44] |
| By 1850 Ma | Eukaryotic cells, containing membrane-boundorganelles with diverse functions, probably derived from prokaryotes engulfing each other viaphagocytosis. (SeeSymbiogenesis andEndosymbiont). Bacterial viruses (bacteriophages) emerge before or soon after the divergence of the prokaryotic and eukaryotic lineages.[45]Red beds show an oxidising atmosphere, favouring the spread of eukaryotic life.[46][47][48] |
| 1500 Ma | Volyn biota, a collection of exceptionally well-preservedmicrofossils with varying morphologies.[49] |
| 1300 Ma | Earliest landfungi.[50] |
| By 1200 Ma | Meiosis andsexual reproduction in single-celled eukaryotes, possibly even in the common ancestor of all eukaryotes[51] or in theRNA world.[52]Sexual reproduction may have increased the rate of evolution.[53] |
| By 1000 Ma | First non-marine eukaryotes move onto land. They were photosynthetic and multicellular, indicating that plants evolved much earlier than originally thought.[54] |
| 750 Ma | Beginning ofanimal evolution.[55][56] |
| 720–630 Ma | Possibleglobal glaciation[57][58] which increased the atmosphericoxygen and decreasedcarbon dioxide, and was eithercaused by land plant evolution[59] orresulted in it.[60] Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution.[61][62][63] |
| 600 Ma | Accumulation of atmospheric oxygen allows the formation of anozone layer.[64] Previous land-based life would probably have required other chemicals to attenuateultraviolet radiation.[43] |
| 580–542 Ma | Ediacaran biota, the first large, complex aquatic multicellular organisms.[65] |
| 580–500 Ma | Cambrian explosion: most modern animalphyla appear.[66][67] |
| 550–540 Ma | Ctenophora (comb jellies),[68]Porifera (sponges),[69]Anthozoa (corals andsea anemones),[70]Ikaria wariootia (an earlyBilaterian).[71] |
539 Ma – present
ThePhanerozoic Eon (Greek: 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, thePaleozoic,Mesozoic andCenozoic, with majormass extinctions at division points.
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538.8 Ma – 251.9 Ma and contains theCambrian,Ordovician,Silurian,Devonian,Carboniferous andPermian periods.
| Date | Event |
|---|---|
| 535 Ma | Major diversification of living things in the oceans:arthropods (e.g. trilobites,crustaceans),chordates,echinoderms,molluscs,brachiopods,foraminifers andradiolarians, etc. |
| 530 Ma | The first known footprints on land date to 530 Ma.[75] |
| 520 Ma | Earliestgraptolites.[76] |
| 511 Ma | Earliestcrustaceans.[77] |
| 505 Ma | Fossilization of theBurgess Shale |
| 500 Ma | Jellyfish have existed since at least this time. |
| 485 Ma | First vertebrates with true bones (jawless fishes). |
| 450 Ma | First completeconodonts andechinoids appear. |
| 440 Ma | First agnathan fishes:Heterostraci,Galeaspida, andPituriaspida. |
| 420 Ma | Earliestray-finned fishes,trigonotarbid arachnids, and landscorpions.[78] |
| 410 Ma | First signs of teeth in fish. EarliestNautilida,lycophytes, andtrimerophytes. |
| 488–400 Ma | Firstcephalopods (nautiloids)[79] andchitons.[80] |
| 395 Ma | Firstlichens,stoneworts. Earliestharvestmen,mites,hexapods (springtails) andammonoids. The earliest known tracks on land named theZachelmie trackways which are possibly related toicthyostegalians.[81] |
| 375 Ma | Tiktaalik, a lobe-finned fish with some anatomical features similar to early tetrapods. It has been suggested to be a transitional species between fish and tetrapods.[82] |
| 365 Ma | Acanthostega is one of the earliest vertebrates capable of walking.[83] |
| 363 Ma | By the start of theCarboniferous Period, the Earth begins to resemble its present state. Insects roamed the land and would soon take to the skies;sharks swam the oceans as top predators,[84] and vegetation covered the land, withseed-bearing plants andforests soon to flourish. Four-limbed tetrapods gradually gain adaptations which will help them occupy a terrestrial life-habit. |
| 360 Ma | Firstcrabs andferns. Land flora dominated byseed ferns. The Xinhang forest grows around this time.[85] |
| 350 Ma | First large sharks,ratfishes, andhagfish; first crowntetrapods (with five digits and no fins and scales). |
| 350 Ma | Diversification ofamphibians.[86] |
| 325-335 Ma | FirstReptiliomorpha.[87] |
| 330-320 Ma | Firstamniote vertebrates (Paleothyris).[88] |
| 320 Ma | Synapsids (precursors to mammals) separate fromsauropsids (reptiles) in late Carboniferous.[89] |
| 305 Ma | TheCarboniferous rainforest collapse occurs, causing a minor extinction event, as well as paving the way for amniotes to become dominant over amphibians and seed plants over ferns and lycophytes. Firstdiapsid reptiles (e.g.Petrolacosaurus). |
| 280 Ma | Earliestbeetles, seed plants andconifers diversify whilelepidodendrids andsphenopsids decrease.Terrestrial temnospondyl amphibians and pelycosaurs (e.g.Dimetrodon) diversify in species. |
| 275 Ma | Therapsid synapsids separate from pelycosaur synapsids. |
| 265 Ma | Gorgonopsians appear in the fossil record.[90] |
| 251.9–251.4 Ma | ThePermian–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 30 million years to completely recover.[91] |
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From 251.9 Ma to 66 Ma and containing theTriassic,Jurassic andCretaceous periods.
| Date | Event |
|---|---|
| 250 Ma | Mesozoic marine revolution begins: increasingly well adapted and diverse predators stresssessile marine groups; the "balance of power" in the oceans shifts dramatically as some groups of prey adapt more rapidly and effectively than others. |
| 250 Ma | Triadobatrachus massinoti is the earliest known frog. |
| 248 Ma | Sturgeon andpaddlefish (Acipenseridae) first appear. |
| 245 Ma | Earliestichthyosaurs |
| 240 Ma | Increase in diversity ofcynodonts andrhynchosaurs |
| 225 Ma | Earliest dinosaurs (prosauropods), firstcardiidbivalves, diversity incycads,bennettitaleans, and conifers. Firstteleost fishes. First mammals (Adelobasileus). |
| 220 Ma | Seed-producingGymnosperm forests dominate the land; herbivores grow to huge sizes to accommodate the large guts necessary to digest the nutrient-poor plants.[citation needed] Firstflies andturtles (Odontochelys). Firstcoelophysoid dinosaurs. Firstmammals from small-sizedcynodonts, which transitioned towards a nocturnal, insectivorous, and endothermic lifestyle. |
| 205 Ma | Massive Triassic/Jurassic extinction. It wipes out allpseudosuchians exceptcrocodylomorphs, who transitioned to an aquatic habitat, whiledinosaurs took over the land andpterosaurs filled the air. |
| 200 Ma | First accepted evidence forviruses infecting eukaryotic cells (the groupGeminiviridae).[92] However, 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 ofarmoured dinosaurs. |
| 195 Ma | First pterosaurs with specialized feeding (Dorygnathus). Firstsauropod dinosaurs. Diversification in small,ornithischian dinosaurs:heterodontosaurids,fabrosaurids, andscelidosaurids. |
| 190 Ma | Pliosauroids appear in the fossil record. Firstlepidopteran insects (Archaeolepis),hermit crabs, modernstarfish, irregular echinoids,corbulid bivalves, andtubulipore bryozoans. Extensive development ofsponge reefs. |
| 176 Ma | FirstStegosaurian dinosaurs. |
| 170 Ma | Earliestsalamanders,newts,cryptoclidids,elasmosauridplesiosaurs, andcladotherian mammals. Sauropod dinosaurs diversify. |
| 168 Ma | Firstlizards. |
| 165 Ma | Firstrays andglycymeridid bivalves. Firstvampire squids.[93] |
| 163 Ma | Pterodactyloid pterosaurs first appear.[94] |
| 161 Ma | Ceratopsian dinosaurs appear in the fossil record (Yinlong) and the oldest known eutherian mammal:Juramaia. |
| 160 Ma | Multituberculate mammals (genusRugosodon) appear in easternChina. |
| 155 Ma | First blood-sucking insects (ceratopogonids),rudist bivalves, andcheilostome bryozoans.Archaeopteryx, a possible ancestor to the birds, appears in the fossil record, along withtriconodontid andsymmetrodont mammals. Diversity instegosaurian andtheropod dinosaurs. |
| 131 Ma | Firstpine trees. |
| 140 Ma | Orb-weaver spiders appear. |
| 135 Ma | Rise of theangiosperms. Some of these flowering plants bear structures that attract insects and other animals to spreadpollen; other angiosperms are pollinated by wind or water. This innovation causes a major burst of animalcoevolution. First freshwaterpelomedusid turtles. Earliestkrill. |
| 120 Ma | Oldest fossils ofheterokonts, including both marinediatoms andsilicoflagellates. |
| 115 Ma | Firstmonotreme mammals. |
| 114 Ma | Earliestbees.[95] |
| 112 Ma | Xiphactinus, a large predatory fish, appears in the fossil record. |
| 110 Ma | Firsthesperornithes, toothed diving birds. Earliestlimopsid,verticordiid, andthyasirid bivalves. |
| 100 Ma | Firstants.[96] |
| 100–95 Ma | Spinosaurus appears in the fossil record.[97] |
| 95 Ma | Firstcrocodilians evolve.[98] |
| 90 Ma | Extinction of ichthyosaurs. Earliestsnakes andnuculanid bivalves. Large diversification in angiosperms:magnoliids,rosids,hamamelidids,monocots, andginger. Earliest examples ofticks. Probable origins ofplacental mammals (earliest undisputed fossil evidence is 66 Ma). |
| 86–76 Ma | Diversification of therian mammals.[99][100] |
| 70 Ma | Multituberculate mammals increase in diversity. Firstyoldiid bivalves. First possibleungulates (Protungulatum). |
| 68–66 Ma | Tyrannosaurus, the largest terrestrial predator of westernNorth America, appears in the fossil record. First species ofTriceratops.[101] |
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| Date | Event |
|---|---|
| 66 Ma | TheCretaceous–Paleogene extinction event eradicates about half of all animal species, includingmosasaurs, pterosaurs, plesiosaurs,ammonites,belemnites, rudist andinoceramid bivalves, most planktic foraminifers, and all of the dinosaurs excluding the birds.[102] |
| 66 Ma | Rapid dominance of conifers andginkgos in high latitudes, along with mammals becoming the dominant species. Firstpsammobiid bivalves. Earliestrodents. Rapid diversification in ants. |
| 63 Ma | Evolution of thecreodonts, an important group of meat-eating (carnivorous) mammals. |
| 62 Ma | Evolution of the firstpenguins. |
| 60 Ma | Diversification of large,flightless birds. Earliest trueprimates,[who?] along with the firstsemelid bivalves,edentate,carnivoran andlipotyphlan mammals, andowls. The ancestors of the carnivorous mammals (miacids) were alive.[citation needed] |
| 59 Ma | Earliestsailfish appear. |
| 56 Ma | Gastornis, a large flightless bird, appears in the fossil record. |
| 55 Ma | Modern bird groups diversify (firstsong birds,parrots,loons,swifts,woodpeckers), firstwhale (Himalayacetus), earliestlagomorphs,armadillos, appearance ofsirenian,proboscidean mammals in the fossil record. Flowering plants continue to diversify. The ancestor (according to theory) of the species in the genusCarcharodon, the earlymako sharkIsurus hastalis, is alive. Ungulates split intoartiodactyla andperissodactyla, withsome members of the former returning to the sea. |
| 52 Ma | Firstbats appear (Onychonycteris). |
| 50 Ma | Peak diversity of dinoflagellates andnannofossils, increase in diversity ofanomalodesmatan and heteroconch bivalves,brontotheres,tapirs,rhinoceroses, andcamels appear in the fossil record, diversification of primates. |
| 40 Ma | Modern-typebutterflies andmoths appear. Extinction ofGastornis.Basilosaurus, one of the first of the giant whales, appeared in the fossil record. |
| 38 Ma | Earliestbears. |
| 37 Ma | Firstnimravid ("false saber-toothed cats") carnivores — these species are unrelated to modern-typefelines. Firstalligators andruminants. |
| 35 Ma | Grasses diversify from among the monocotangiosperms;grasslands begin to expand. Slight increase in diversity of cold-tolerantostracods and foraminifers, along with major extinctions ofgastropods, reptiles, amphibians, and multituberculate mammals. Many modern mammal groups begin to appear: firstglyptodonts,ground sloths,canids,peccaries, and the firsteagles andhawks. Diversity intoothed andbaleen whales. |
| 33 Ma | Evolution of thethylacinidmarsupials (Badjcinus). |
| 30 Ma | Firstbalanids andeucalypts, extinction ofembrithopod and brontothere mammals, earliestpigs andcats. |
| 28 Ma | Paraceratherium appears in the fossil record, the largest terrestrial mammal that ever lived. Firstpelicans. |
| 25 Ma | Pelagornis sandersi appears in the fossil record, the largest flying bird that ever lived. |
| 25 Ma | Firstdeer. |
| 24 Ma | Firstpinnipeds. |
| 23 Ma | Earliestostriches, trees representative of most major groups ofoaks have appeared by now.[103] |
| 20 Ma | Firstgiraffes,hyenas, andgiant anteaters, increase in bird diversity. |
| 17 Ma | First birds of the genusCorvus (crows). |
| 15 Ma | GenusMammut appears in the fossil record, firstbovids andkangaroos, diversity inAustralian megafauna. |
| 10 Ma | Grasslands andsavannas are established, diversity in insects, especially ants andtermites,horses increase in body size and develophigh-crowned teeth, major diversification in grassland mammals and snakes. |
| 9.5 Ma [dubious –discuss] | Great American Interchange, where various land and freshwater faunas migrated between North andSouth America. Armadillos,opossums,hummingbirdsPhorusrhacids,Ground Sloths,Glyptodonts, andMeridiungulates traveled to North America, whilehorses,tapirs,saber-toothed cats,jaguars,bears,coaties,ferrets,otters,skunks and deer entered South America. |
| 9 Ma | Firstplatypuses. |
| 6.5 Ma | Firsthominins (Sahelanthropus). |
| 6 Ma | Australopithecines diversify (Orrorin,Ardipithecus). |
| 5 Ma | Firsttree sloths andhippopotami, diversification of grazing herbivores likezebras andelephants, large carnivorous mammals likelions and the genusCanis, burrowing rodents, kangaroos, birds, and small carnivores,vultures increase in size, decrease in the number of perissodactyl mammals. Extinction of nimravid carnivores. Firstleopard seals. |
| 4.8 Ma | Mammoths appear in the fossil record. |
| 4.5 Ma | Marine iguanas diverge from land iguanas. |
| 4 Ma | Australopithecus evolves.Stupendemys appears in the fossil record as the largest freshwater turtle, first modern elephants, giraffes, zebras, lions, rhinoceros andgazelles appear in the fossil record |
| 3.6 Ma | Blue whales grow to modern size. |
| 3 Ma | Earliestswordfish. |
| 2.7 Ma | Paranthropus evolves. |
| 2.5 Ma | Earliest species ofArctodus andSmilodon evolve. |
| 2 Ma | First members of genusHomo,Homo Habilis, appear in the fossil record. Diversification of conifers in high latitudes. The eventual ancestor of cattle,aurochs (Bos primigenus), evolves in India. |
| 1.7 Ma | Australopithecines go extinct. |
| 1.2 Ma | Evolution ofHomo antecessor. The last members ofParanthropus die out. |
| 1.0 Ma | Firstcoyotes. |
| 810 ka | Firstwolves |
| 600 ka | Evolution ofHomo heidelbergensis. |
| 400 ka | Firstpolar bears. |
| 350 ka | Evolution ofNeanderthals. |
| 300 ka | Gigantopithecus, a giant relative of theorangutan fromAsia dies out. |
| 250 ka | Anatomically modern humans appear inAfrica.[104][105][106] Around 50 ka they start colonising the other continents, replacing Neanderthals inEurope and other hominins in Asia. |
| 70 ka | Genetic bottleneck in humans (Toba catastrophe theory). |
| 40 ka | Last giant monitor lizards (Varanus priscus) die out. |
| 35–25 ka | Extinction ofNeanderthals. Domestication ofdogs. |
| 15 ka | Lastwoolly rhinoceros (Coelodonta antiquitatis) are believed to have gone extinct. |
| 11 ka | Short-faced bears vanish from North America, with the lastgiant ground sloths dying out. AllEquidae become extinct in North America. Domestication of variousungulates. |
| 10 ka | Holoceneepoch starts[107] after theLast Glacial Maximum. Last mainland species ofwoolly mammoth (Mammuthus primigenus) die out, as does the lastSmilodon species. |
| 8 ka | Thegiant lemur dies out. |
Because the Moon helps stabilize the tilt of the Earth's rotation, it prevents the Earth from wobbling between climatic extremes. Without the Moon, seasonal shifts would likely outpace even the most adaptable forms of life.
{{cite journal}}: CS1 maint: multiple names: authors list (link)The researchers found that land plants had evolved on Earth by about 700 million years ago and land fungi by about 1,300 million years ago — much earlier than previous estimates of around 480 million years ago, which were based on the earliest fossils of those organisms.
The oldest fossils of footprints ever found on land hint that animals may have beaten plants out of the primordial seas. Lobster-sized, centipede-like animals made the prints wading out of the ocean and scuttling over sand dunes about 530 million years ago. Previous fossils indicated that animals didn't take this step until 40 million years later.
The ancestry of sharks dates back more than 200 million years before the earliest known dinosaur.
Viruses of nearly all the major classes of organisms - animals, plants, fungi and bacteria / archaea - probably evolved with their hosts in the seas, given that most of the evolution of life on this planet has occurred there. This means that viruses also probably emerged from the waters with their different hosts, during the successive waves of colonisation of the terrestrial environment.
The model shows that modern bees started diversifying at a breakneck pace about 114 million years ago, right around the time that eudicots—the plant group that comprises 75 percent of flowering plants—started branching out. The results, which confirm some earlier genetic studies, strengthen the case that flowering plants and pollinating bees have coevolved from the very beginning.
