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GEOLOGIC TIME SCALE: FROM 4600 MILLION YEARS AGO TO PRESENT

millions of years ago era period notes

4600 ^ Precambrian Precambrian The formation of the | . . Earth's crust and the | . . subsequent evolution of | . . life | 4550 + | \ (Note: Precambrian era lasts from 4600 million years ago to 570 / million years ago, a span of over four billion years. A time- \ line showing this would extend another 403 lines, or roughly 7 / pages.) | 600 + | | | Palaeozoic Cambrian Marine animals with | . . mineralized shells 550 + . . appear: trilobites, | . . echinoderms, brachio- | pods, molluscs, | primitive graptolites; | a variety of worms 500 + Ordovician Graptolites dominant; | . also trilobites, | . brachiopods, bryozoans, | . gastropods, bivalves, | echinoids, crinoids, 450 + cephalopods, and corals | Silurian Barchiopods, crinoids, | . corals, corals; prim- | . itive fish | . 400 + Devonian (395) Corals, brachiopods, | . ammonoids, crinoids; | . fishes and early land | . plants | 350 + Carboniferous (345) Foraminiferans, corals, | . bryozoans, brachiopods, | . blastoids; seed ferns, | . lycopsids, and other | plants; amphibians 300 + become more common | | Permian Trilobites extinct; | . Amphibians and reptiles | . dominant land animals; 250 + . gymnosperms dominant | plants | Mesozoic Triassic Molluscs dominant | . . invertebrates; reptiles | . . dominant: turtles, 200 + . . dinosaurs, ichthyosaurs | Jurassic Ferns, cycads, ginkgos, | . rushes, conifers; ammo- | . nites and other inver- | . tebrates; pterosaurs, 150 + _Archaeopteryx_ appears | Cretaceous (136) Angiosperm plants; | . Mesozoic reptiles peak | . | . 100 + | | | Cenozoic Tertiary (65) Mass extinction: dino- | . . saurs, pterosaurs, and 50 + . . ammonites extinct; rise | . . of modern animals; | shrubs, grasses, and | other flowering plants | . PRESENT + Quarternary (1.8) . v

INSET: CENOZOIC ERA

millions of years ago era period epoch notes

^ | 65 + Cenozoic Tertiary Palaeocene Mammals become abundant | . . . after extinction of | . . . dinosaurs and large | . . . reptiles; by the | beginning of the Eocene 60 + rodents and primates | have evolved | | | 55 + | Eocene Mammals dominant: | . rodents, artiodactyls, | . carnivores, perisso- | . dactyls (including 50 + horses); whales make | their first appearance | | | 45 + | | | | 40 + | | Oligocene Continued rise of | . mammals: pigs, | . rhinoceroses, and 35 + . tapirs make their | appearance | | | 30 + | | | | Miocene More and more modern 25 + . mammals: horses, dogs | . and bears, modern | . whales, South American | monkeys; modern birds, | apes present in 20 + southern Europe, | _Ramapithecus_ appears | | | 15 + | | | | 10 + | | | Pliocene Mammals similar to | . modern forms evolve; 5 + . australopithecines | . appear, the forerunners | of humanity, appear | Quarternary Pleistocene (1.8) Ice ages; _Homo | . . sapiens_ evolves PRESENT + . Holocene (0.01) Human history v