पृथ्वी पर जीवन के अस्तित्व का इतिहास

thumb|पृथ्वी पर जीवन के इतिहास का एक स्पाइरल के रूप में दृष्यात्मक निरूपण

 मूलभूत समयरेखा
पृथ्वी के 

4.6 बिलियन वर्ष इतिहास में जीवन का इतिहास इस प्रकार है-

 पिछले 3.6 बिलियन वर्षों तक, सरल कोशिकाएँ (prokaryotes);
 पिछले 3.4 बिलियन वर्षों तक, स्यानोबैकेटीरिया (cyanobacteria) प्रकाश संश्लेषण करता रहा;
 पिछले 2 बिलियन वर्षों तक, जटिल कोशिकाएँ (eukaryotes);
 for the last 1 billion years, multicellular life;
 पिछले 600 मिलियन वर्षों तक, सरल जन्तु;
 for the last 550 million years, bilaterians, water life forms with a front and a back;
 for the last 500 million years, fish and proto-amphibians;
 for the last 475 million years, land plants;
 for the last 400 million years, insects and seeds;
 for the last 360 million years, amphibians;
 for the last 300 million years, reptiles;
 for the last 200 million years, mammals;
 for the last 150 million years, birds;
 for the last 130 million years, flowers;
 for the last 60 million years, the primates, 
 for the last 20 million years, the family Hominidae (great apes);
 for the last 2.5 million years, the genus Homo (human predecessors);
 for the last 200,000 years, anatomically modern humans.

Periodic extinctions have temporarily reduced diversity, eliminating:
 2.4 billion years ago, many obligate anaerobes, in the oxygen catastrophe;
 252 million years ago, the trilobites, in the Permian–Triassic extinction event;
 66 million years ago, the pterosaurs and nonavian dinosaurs, in the Cretaceous–Paleogene extinction event.
Dates are approximate.

 विस्तृत समयरेखा 
In this timeline, Ma (for megaannum) means "million years ago", ka (for kiloannum) means "thousand years ago", and ya means "years ago".

 Hadean Eon 

4000 Ma and earlier.

 Date Event 4600 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. 4500 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.Planetary Science Institute page  on the Giant Impact Hypothesis. Hartmann and Davis belonged to the PSI. This page also contains several paintings of the impact by Hartmann himself. The gravitational pull of the new Moon stabilises the Earth's fluctuating axis of rotation and sets up the conditions in which life formed."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."
  Astrobiology Magazine. (URL accessed on August 7, 2010)

 Archean Eon 

4000 Ma – 2500 Ma

 Date Event 4000 Ma Formation of Greenstone belt of the Acasta Gneiss of the Great Slave Region, in Canada, the oldest rock belt in the world.Bjornerud, Marcia, (2005), "Reading the Rocks: the autobiography of the Earth" (Basic Books 4100–3800 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's emergence and early diversification. 3900–2500 Ma Cells resembling prokaryotes appear.Carl Woese, J Peter Gogarten, "When did eukaryotic cells (cells with nuclei and other internal organelles) first evolve? What do we know about how they evolved from earlier life-forms? " Scientific American, October 21, 1999. 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. 3800 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. The earliest evidences for life on Earth are graphite found to be biogenic in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. 3500 Ma Lifetime of the last universal ancestor;Doolittle, W. Ford (February, 2000). Uprooting the tree of life. Scientific American 282 (6): 90–95.Nicolas Glansdorff, Ying Xu & Bernard Labedan: The Last Universal Common Ancestor : emergence, constitution and genetic legacy of an elusive forerunner. Biology Direct 2008, 3:29. the split between bacteria and archaea occurs.

Bacteria develop primitive forms of photosynthesis which at first do not produce oxygen. 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 a 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  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 

 Proterozoic Eon 

2500 Ma – 542 Ma

 Date Event 2500 Ma Great Oxidation Event led by Cyanobacteria's oxygenic photosynthesis. Commencement of plate tectonics with old marine crust dense enough to subduct. 2000 Ma Diversification and expansion of acritarchs. By 1850 Ma Eukaryotic cells appear. Eukaryotes contain membrane-bound organelles with diverse functions, probably derived from prokaryotes engulfing each other via phagocytosis. (See Endosymbiosis). 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.p.151, Bjornerund, Marcia (2005), "Reading the Rocks: the autobiography of the Earth" (Basic Books) 1400 Ma Great increase in stromatolite diversity.  By 1200 Ma Meiosis and sexual reproduction are present in single-celled eukaryotes, and possibly in the common ancestor of all eukaryotes.Bernstein H, Bernstein C, Michod RE (2012). DNA repair as the primary adaptive function of sex in bacteria and eukaryotes. Chapter 1: pp.1-49 in: DNA Repair: New Research, Sakura Kimura and Sora Shimizu editors. Nova Sci. Publ., Hauppauge, N.Y. ISBN 978-1-62100-808-8 https://www.novapublishers.com/catalog/product_info.php?products_id=31918  Sex may even have arisen earlier in the RNA world.Bernstein H, Byerly HC, Hopf FA, Michod RE. (1984). Origin of sex. J Theor Biol. 110(3):323-51. PMID 6209512 Sexual reproduction first appears in the fossil records; it may have increased the rate of evolution. 1200 Ma Simple multicellular organisms evolve, mostly consisting of cell colonies of limited complexity. First multicellular red algae evolve 1100 Ma Earliest dinoflagellates 1000 Ma First vaucherian algae (ex: Palaeovaucheria) 750 Ma First protozoa (ex: Melanocyrillium) 850–630 Ma A global glaciation may have occurred. Full online article (pdf 260 Kb) <ref
 name=Kirschvink1992></ref> Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution. 600 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. 580–542 Ma The Ediacaran biota represent the first large, complex multicellular organisms — although their affinities remain a subject of debate. 580–500 Ma Most modern phyla of animals begin to appear in the fossil record during the Cambrian explosion. 560 Ma Earliest fungi 550 Ma First fossil evidence for ctenophora (comb jellies), porifera (sponges), and anthozoa (corals & anemones)

 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.

 पुराजीवी महाकल्प 

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."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 or slug like animals such as Protichnites and Climactichnites 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." Oldest fossil footprints on land  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 First complete conodonts and echinoids appear. 440 Ma First agnathan fishes: Heterostraci, Galeaspida, and Pituriaspida. 434 Ma The first primitive plants move onto land,"The oldest fossils reveal evolution of non-vascular plants by the middle to late Ordovician Period (~450–440 Ma) on the basis of fossil spores" Transition of plants to land  having evolved from green algae living along the edges of lakes."The land plants evolved from the algae, more specifically green algae, as suggested by certain common
biochemical traits" The first land plants  They are accompanied by fungi, which may have aided the colonization 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. The first known tetrapod tracks on land. 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,"The ancestry of sharks dates back more than 200 million years before the earliest known dinosaur. Introduction to shark evolution, geologic time and age determination  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). 320 Ma Synapsids (pre-cursors to mammals) separate from sauropsids (reptiles) in late Carboniferous. 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. 275 Ma Therapsids separate from synapsids. 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.

 मध्यजीवी महाकल्प 

 Date Event From 251.4 Ma The 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. 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. First mammals (Adelobasileus). 220 Ma Gymnosperm forests dominate the land; herbivores grow to huge sizes to accommodate the large guts necessary to digest the nutrient-poor plants., first flies and turtles (Odontochelys). First Coelophysoid dinosaurs 200 Ma The first accepted evidence for viruses that infect eukaryotic cells (at least, the group Geminiviridae) exists."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." Origins of Viruses  (URL accessed on January 9, 2005) 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. Sauropod dinosaurs diversify. 165 Ma First rays and glycymeridid bivalves. 163 Ma Pterodactyloid pterosaurs first appear. 161 Ma Ceratopsian dinosaurs appear in the fossil record (Yinlong) 155 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. 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. 120 Ma Oldest fossils of heterokonts, including both marine diatoms and silicoflagellates. 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. Probable origins of placental mammals (earliest undisputed fossil evidence is 66 Ma). 80 Ma First ants. 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.

 नूतनजीवी महाकल्प 

66 Ma – present

 Date Event 66 MaThe Cretaceous–Paleogene 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. From 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. 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 Pelagornis sandersi appears in the fossil record, the largest bird that ever lived. 25 Ma First deer. 20 Ma First giraffes, hyenas, bears 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 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 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, first modern elephants, giraffes, zebras, lions, rhinos and gazelles appear in the fossil record.  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 primigenus 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.The Oldest Homo Sapiens:  - URL retrieved May 15, 2009 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, first domestic dogs. 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 years ago after the Late Glacial Maximum. The last mainland species of Woolly mammoth (Mammuthus primigenus) die out, as does the last Smilodon species

ऐतिहासिक विलोपन (Historical extinctions)
 Date Event 6000 ya 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 c. 600 ya (c. 1400) The moa and its predator, Haast's Eagle, die out in New Zealand  ya (1627) The last recorded wild Aurochs die out  ya (1688) The dodo goes extinct  ya (1768) The Steller's sea cow goes extinct  ya (1883) The quagga, a subspecies of zebra, goes extinct  ya (1914) Martha, last known Passenger Pigeon, dies  ya (1936) The Thylacine goes extinct in a Tasmanian zoo, the last member of the family Thylacinidae  ya (1952) The Caribbean monk seal goes extinct"It's official: Caribbean monk seal is extinct", MSNBC.com  6 जून 2008  ya (2008) The Baiji, the Yangtze river dolphin, becomes functionally extinct

 इन्हें भी देखें
 भूवैज्ञानिक समय-मान
 पृथ्वी का इतिहास
 कार्बन-१४ द्वारा कालनिर्धारण
 प्राकृतिक इतिहास

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

सन्दर्भ

बाहरी कड़ियाँ
 Berkeley Evolution
 Evolution Timeline
 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
 John Kyrk's Timeline from Big Bang to present
 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

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