The evolutionary history of life on Earth traces the processes by which living and fossil organisms have evolved since life on the planet first originated until the present day. Earth formed about 4.5 Ga (billion years ago) and life appeared on its surface within 1 billion years. The similarities between all present-day organisms indicate the presence of a common ancestor from which all known species have diverged through the process of evolution.
\nMicrobial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean and many of the major steps in early evolution are thought to have taken place within them. The evolution of oxygenic photosynthesis, around 3.5 Ga, eventually led to the oxygenation of the atmosphere, beginning around 2.4 Ga. The earliest evidence of eukaryotes (complex cells with organelles) dates from 1.85 Ga, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions. Bilateria, animals with a front and a back, appeared by 555 million years ago.
\nThe earliest land plants date back to around 450 Ma (million years ago), although evidence suggests that algal scum formed on the land as early as 1.2 Ga. Land plants were so successful that they are thought to have contributed to the late Devonian extinction event. Invertebrate animals appear during the Ediacaran period, while vertebrates originated about 525 Ma during the Cambrian explosion. During the Permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the Permian\u2013Triassic extinction event 252.2 Ma. During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates, displacing therapsids in the mid-Triassic; one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods. After the Cretaceous\u2013Paleogene extinction event 66 Ma killed off the dinosaurs, mammals increased rapidly in size and diversity. Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.
\nFossil evidence indicates that flowering plants appeared and rapidly diversified in the Early Cretaceous (130 to 90 Ma) probably helped by coevolution with pollinating insects. Flowering plants and marine phytoplankton are still the dominant producers of organic matter. Social insects appeared around the same time as flowering plants. Although they occupy only small parts of the insect “family tree”, they now form over half the total mass of insects. Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over 6 Ma. Although early members of this lineage had chimpanzee-sized brains, there are signs of a steady increase in brain size after about 3 Ma.<\/p>\n
TIMELINE OF THE EVOLUTIONARY HISTORY OF EARTH<\/strong> Basic timeline<\/strong> Periodic extinctions<\/strong> have temporarily reduced diversity, eliminating: Hadean Eon<\/strong> 4000 Ma and earlier. Historical extinctions<\/strong> Did Dark Matter Kill the Dinosaurs?<\/strong> It is well accepted that a meteorite collided with the earth 65 million years ago causing the dinosaur die-off. But a new reason for the meteorite may be dark matter \u2013 that not fully-explained stuff that makes up 85% of all matter and is believed to surround galaxies in a sort of sphere, holding them together. A new model of a different type dark matter interacts electronically and exists in a thin layer in the middle of the Milky Way, sandwiched between its top and bottom halves. The evolutionary history of life on Earth traces the processes by which living and fossil organisms have evolved since life on the planet first originated until the present day. Earth formed about 4.5 Ga (billion years ago) and life appeared … Continue reading
\nAxis scale: millions of years ago.
\nDates prior to 1000 million years ago are speculative.
\nThis timeline of evolution of life represents current scientific theory outlining the major events in the development of life on planet Earth. In biology, evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, and individual organisms and molecules such as DNA and proteins. The similarities between all present day organisms indicate the presence of a common ancestor from which all known species, living and extinct, have diverged through the process of evolution.
\nThe dates given in this article are estimates based on scientific evidence.<\/p>\n
\nIn its 4.6 billion years circling the sun, the Earth has harbored an increasing diversity of life forms:
\nfor the last 3.6 billion years, simple cells (prokaryotes);
\nfor the last 3.4 billion years, cyanobacteria performing photosynthesis;
\nfor the last 2 billion years, complex cells (eukaryotes);
\nfor the last 1 billion years, multicellular life;
\nfor the last 600 million years, simple animals;
\nfor the last 550 million years, bilaterians, animals with a front and a back;
\nfor the last 500 million years, fish and proto-amphibians;
\nfor the last 475 million years, land plants;
\nfor the last 400 million years, insects and seeds;
\nfor the last 360 million years, amphibians;
\nfor the last 300 million years, reptiles;
\nfor the last 200 million years, mammals;
\nfor the last 150 million years, birds;
\nfor the last 130 million years, flowers;
\nfor the last 60 million years, the primates,
\nfor the last 20 million years, the family Hominidae (great apes);
\nfor the last 2.5 million years, the genus Homo (human predecessors);
\nfor the last 200,000 years, anatomically modern humans.<\/p>\n
\n2.4 billion years ago, many obligate anaerobes, in the oxygen catastrophe;
\n252 million years ago, the trilobites, in the Permian\u2013Triassic extinction event;
\n66 million years ago, the pterosaurs and nonavian dinosaurs, in the Cretaceous\u2013Paleogene extinction event.
\nDates are approximate.
\nIn this timeline, Ma (for megaannum) means “million years ago”, ka (for kiloannum) means “thousand years ago”, and ya means “years ago”.<\/p>\n
\n4600 Ma The planet Earth forms from the accretion disc revolving around the young Sun; complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth.
\n4500 Ma According to the giant impact hypothesis the moon is formed when the planet Earth and the planet Theia collide, sending a very large number of moonlets into orbit around the young Earth which eventually coalesce to form the Moon. The gravitational pull of the new Moon stabilises the Earth’s fluctuating axis of rotation and sets up the conditions in which life formed.
\nArchean Eon<\/strong> 4000 Ma \u2013 2500 Ma
\n4000 Ma Formation of Greenstone belt of the Acasta gneisses of the Great Slave Region, in Canada, the oldest rock belt in the world.
\n4100\u20133800 Ma Late Heavy Bombardment: extended barrage of impact events upon the inner planets by meteoroids. Thermal flux from widespread hydrothermal activity during the LHB may have been conducive to life\u2019s emergence and early diversification.
\n3900\u20132500 Ma Cells resembling prokaryotes appear. 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.
\n3800 Ma Formation of Greenstone belt of the Isua complex of the western Greenland Region, whose rocks show an isotope frequency suggestive of the presence of life.
\n3500 Ma Lifetime of the last universal ancestor; the split between bacteria and archaea occurs.
\nBacteria develop primitive forms of photosynthesis which at first do not produce oxygen.[12] These organisms generate ATP by exploiting a proton gradient, a mechanism still used in virtually all organisms.
\n3000 Ma Photosynthesizing cyanobacteria evolve; they use water as a reducing agent, thereby producing oxygen as waste product. The oxygen initially oxidizes dissolved iron in the oceans, creating iron ore. The oxygen concentration in the atmosphere slowly rises, acting as a poison for many bacteria. The Moon is still very close to 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). Life on land likely developed at this time.
\nProterozoic Eon<\/strong> 2500 Ma \u2013 542 Ma
\n2500 Ma Great Oxidation Event led by Cyanobacteria’s oxygenic photosynthesis. Commencement of plate tectonics with old marine crust dense enough to subduct.
\n2000 Ma Diversification and expansion of acritarchs.
\nBy 1850 Ma Eukaryotic cells appear. Eukaryotes contain membrane-bound organelles with diverse functions, probably derived from prokaryotes engulfing each other via phagocytosis. Bacterial viruses (bacteriophage) emerge before, or soon after, the divergence of the prokaryotic and eukaryotic lineages. The appearance of red beds show that an oxidising atmosphere had been produced. Incentives now favoured the spread of eukaryotic life.
\n1400 Ma Great increase in stromatolite diversity.
\nBy 1200 Ma Meiosis and sexual reproduction are present in single-celled eukaryotes, and possibly in the common ancestor of all eukaryotes. Sex may even have arisen earlier in the RNA world. Sexual reproduction first appears in the fossil records; it may have increased the rate of evolution.
\n1200 Ma Simple multicellular organisms evolve, mostly consisting of cell colonies of limited complexity. First multicellular red algae evolve
\n1100 Ma Earliest dinoflagellates
\n1000 Ma First vaucherian algae (ex: Palaeovaucheria)
\n750 Ma First protozoa (ex: Melanocyrillium)
\n850\u2013630 Ma A global glaciation may have occurred. Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution.
\n600 Ma The accumulation of atmospheric oxygen allows the formation of an ozone layer. Prior to this, land-based life would probably have required other chemicals to attenuate ultraviolet radiation enough to permit colonisation of the land.
\n580\u2013542 Ma The Ediacaran biota represent the first large, complex multicellular organisms \u2014 although their affinities remain a subject of debate.
\n580\u2013500 Ma Most modern phyla of animals begin to appear in the fossil record during the Cambrian explosion.
\n560 Ma Earliest fungi
\n550 Ma First fossil evidence for ctenophora (comb jellies), porifera (sponges), and anthozoa (corals & anemones)
\nPhanerozoic Eon<\/strong> 542 Ma \u2013 present
\nThe 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.
\nPaleozoic Era<\/strong> 542 Ma \u2013 251.0 Ma
\n535 Ma Major diversification of living things in the oceans: chordates, arthropods (e.g. trilobites, crustaceans), echinoderms, mollusks, brachiopods, foraminifers and radiolarians, etc.
\n530 Ma The first known footprints on land date to 530 Ma, indicating that early animal explorations may have predated the development of terrestrial plants.
\n525 Ma Earliest graptolites.
\n510 Ma First cephalopods (Nautiloids) and chitons.
\n505 Ma Fossilization of the Burgess Shale.
\n485 Ma First vertebrates with true bones (jawless fishes).
\n450 Ma First complete conodonts and echinoids appear.
\n440 Ma First agnathan fishes: Heterostraci, Galeaspida, and Pituriaspida.
\n434 Ma The first primitive plants move onto land, having evolved from green algae living along the edges of lakes. They are accompanied by fungi[citation needed], which may have aided the colonization of land through symbiosis.
\n420 Ma Earliest ray-finned fishes, trigonotarbid arachnids, and land scorpions.
\n410 Ma First signs of teeth in fish. Earliest nautiid nautiloids, lycophytes, and trimerophytes.
\n395 Ma First lichens, stoneworts. Earliest harvestman, mites, hexapods (springtails) and ammonoids. The first known tetrapod tracks on land.
\n363 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, and vegetation covered the land, with seed-bearing plants and forests soon to flourish.
\nFour-limbed tetrapods gradually gain adaptations which will help them occupy a terrestrial life-habit.
\n360 Ma First crabs and ferns. Land flora dominated by seed ferns.
\n350 Ma First large sharks, ratfishes, and hagfish.
\n340 Ma Diversification of amphibians.
\n330 Ma First amniote vertebrates (Paleothyris).
\n320 Ma Synapsids separate from sauropsids (reptiles) in late Carboniferous.
\n305 Ma Earliest diapsid reptiles (e.g. Petrolacosaurus).
\n280 Ma Earliest beetles, seed plants and conifers diversify while lepidodendrids and sphenopsids decrease. Terrestrial temnospondyl amphibians and pelycosaurs (e.g. Dimetrodon) diversify in species.
\n275 Ma Therapsids separate from synapsids.
\n251.4 Ma The Permian\u2013Triassic 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.
\nMesozoic Era<\/strong> From 251.4 Ma
\nThe Mesozoic Marine Revolution begins: increasingly well adapted and diverse predators pressurize sessile marine groups; the “balance of power” in the oceans shifts dramatically as some groups of prey adapt more rapidly and effectively than others.
\n245 Ma Earliest ichthyosaurs.
\n240 Ma Increase in diversity of gomphodont cynodonts and rhynchosaurs.
\n225 Ma Earliest dinosaurs (prosauropods), first cardiid bivalves, diversity in cycads, bennettitaleans, and conifers. First teleost fishes. First mammals (Adelobasileus).
\n220 Ma Gymnosperm forests dominate the land; herbivores grow to huge sizes to accommodate the large guts necessary to digest the nutrient-poor plants.[citation needed], first flies and turtles (Odontochelys). First Coelophysoid dinosaurs
\n200 Ma The first accepted evidence for viruses that infect eukaryotic cells (at least, the group Geminiviridae) exists. Viruses are still poorly understood and may have arisen before “life” itself, or may be a more recent phenomenon.
\nMajor extinctions in terrestrial vertebrates and large amphibians. Earliest examples of Ankylosaurian dinosaurs
\n195 Ma First pterosaurs with specialized feeding (Dorygnathus). First sauropod dinosaurs. Diversification in small, ornithischian dinosaurs: heterodontosaurids, fabrosaurids, and scelidosaurids.
\n190 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.
\n176 Ma First members of the Stegosauria group of dinosaurs
\n170 Ma Earliest salamanders, newts, cryptoclidid & elasmosaurid plesiosaurs, and cladotherian mammals. Sauropod dinosaurs diversify.
\n165 Ma First rays and glycymeridid bivalves.
\n161 Ma Ceratopsian dinosaurs appear in the fossil record (Yinlong)
\n155 Ma First blood-sucking insects (ceratopogonids), rudist bivalves, and cheilostome 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.
\n130 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.
\n120 Ma Oldest fossils of heterokonts, including both marine diatoms and silicoflagellates.
\n115 Ma First monotreme mammals.
\n110 Ma First hesperornithes, toothed diving birds. Earliest limopsid, verticordiid, and thyasirid bivalves.
\n106 Ma Spinosaurus, the largest theropod dinosaur, appears in the fossil record.
\n100 Ma Earliest bees.
\n90 Ma Extinction of ichthyosaurs. Earliest snakes and nuculanid bivalves. Large diversification in angiosperms: magnoliids, rosids, hamamelidids, monocots, and ginger. Earliest examples of ticks.
\n80 Ma First ants.
\n70 Ma Multituberculate mammals increase in diversity. First yoldiid bivalves.
\n68 Ma Tyrannosaurus, the largest terrestrial predator of North America appears in the fossil record. First species of Triceratops.
\nCenozoic Era 66 Ma \u2013 present
\n66 Ma The Cretaceous\u2013Paleogene 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.
\nFrom 66 Ma Rapid dominance of conifers and ginkgos in high latitudes, along with mammals becoming the dominant species. First psammobiid bivalves. Rapid diversification in ants.
\n63 Ma Evolution of the creodonts, an important group of carnivorous mammals.
\n60 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.
\n56 Ma Gastornis, a large, flightless bird appears in the fossil record, becoming an apex predator at the time.
\n55 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.
\n52 Ma First bats appear (Onychonycteris).
\n50 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.
\n40 Ma Modern-type butterflies and moths appear. Extinction of Gastornis. Basilosaurus, one of the first of the giant whales, appeared in the fossil record.
\n37 Ma First Nimravid carnivores (“False Saber-toothed Cats”) \u2014 these species are unrelated to modern-type felines
\n35 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.
\n33 Ma Evolution of the thylacinid marsupials (Badjcinus).
\n30 Ma First balanids and eucalypts, extinction of embrithopod and brontothere mammals, earliest pigs and cats.
\n28 Ma Paraceratherium appears in the fossil record, the largest terrestrial mammal that ever lived.
\n25 Ma First deer.
\n20 Ma First giraffes, hyenas, bears and giant anteaters, increase in bird diversity.
\n15 Ma Mammut appears in the fossil record, first bovids and kangaroos, diversity in Australian megafauna.
\n10 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.
\n6.5 Ma First hominin (Sahelanthropus).
\n6 Ma Australopithecines diversify (Orrorin, Ardipithecus)
\n5 Ma First tree sloths and hippopotami, diversification of grazing herbivores like zebras and elephants, large carnivorous mammals like lions and dogs, burrowing rodents, kangaroos, birds, and small carnivores, vultures increase in size, decrease in the number of perissodactyl mammals. Extinction of Nimravid carnivores
\n4.8 Ma Mammoths appear in the fossil record.
\n4 Ma Evolution of Australopithecus, Stupendemys appears in the fossil record as the largest freshwater turtle, first modern elephants, giraffes, zebras, lions, rhinos and gazelles appear in the fossil record.
\n3 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.
\n2.7 Ma Evolution of Paranthropus
\n2.5 Ma The earliest species of Smilodon evolve
\n2 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
\n1.7 Ma Extinction of australopithecines.
\n1.2 Ma Evolution of Homo antecessor. The last members of Paranthropus die out.
\n600 ka Evolution of Homo heidelbergensis
\n350 ka Evolution of Neanderthals
\n300 ka Gigantopithecus, a giant relative of the orangutan dies out from Asia
\n200 ka Anatomically modern humans appear in Africa. Around 50,000 years before present they start colonising the other continents, replacing the Neanderthals in Europe and other hominins in Asia.
\n40 ka The last of the giant monitor lizards (Megalania) die out
\n30 ka Extinction of Neanderthals, first domestic dogs.
\n15 ka The last Woolly rhinoceros (Coelodonta) are believed to have gone extinct
\n11 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
\n10 ka The Holocene Epoch starts 10,000 years ago after the Late Glacial Maximum. The last mainland species of Woolly mammoth (Mammuthus primigenius) die out, as does the last Smilodon species<\/p>\n
\n6000 ya Small populations of American Mastodon die off in places like Utah and Michigan
\n4500 ya The last members of a dwarf race of Woolly Mammoths vanish from Wrangel Island near Alaska
\n613 ya (1400) The moa and its predator, Haast’s Eagle, die out in New Zealand
\n386 ya (1627) The last recorded wild Aurochs die out
\n325 ya (1688) The dodo goes extinct
\n245 ya (1768) The Steller’s sea cow goes extinct
\n130 ya (1883) The quagga, a subspecies of zebra, goes extinct
\n99 ya (1914) Martha, last known Passenger Pigeon, dies
\n77 ya (1936) The Thylacine goes extinct in a Tasmanian zoo, the last member of the family Thylacinidae
\n61 ya (1952) The Caribbean monk seal goes extinct
\n5 ya (2008) The Baiji, the Yangtze river dolphin, becomes functionally extinct<\/p>\n
\nMost of the time that would have no consequence for Earth. But every 35 million years, as our sun orbits the centre of the galaxy, it would cross that dark-matter equator, creating a disturbance that could jostle the comets that hover at the fringes of our solar system, sending one plunging toward Earth. Geological records do suggest heavy cratering on Earth at about those intervals, and fossil records suggest corresponding die-offs.<\/p>\n","protected":false},"excerpt":{"rendered":"