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Era
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Period
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Epoch
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Age
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Life Forms
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Archeozoic
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Precambrian
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4,500-550 mya (millions of years ago)
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First single-celled organisms, simple plants, and invertebrate animals: algae, bacteria, jellyfish, flagellates, amoebas, worms, sponges
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Paleozoic
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Cambrian
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550-505 mya
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First trilobites, forams, brachiopods, nautiloids, clams, snails, crustaceans, crinoids, gastropods, corals, protozoans
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Ordovician
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505-438 mya
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First starfish, sea urchins, blastoids, eurypterids, bryozoa, scaphopods, jawless fish, echinoids
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Silurian
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438-408 mya
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First land plants, ferns, sharks, boney fish, scorpions
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Devonian
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408-360 mya
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First insects, tetrapods, ammonites, placoderms
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Carboniferous
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Mississippian
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360-325 mya
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First reptiles, spiders, amphibians
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Pennsylvanian
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325-286 mya
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First conifers, synapsids
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Permian
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286-248 mya
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Heyday of synapsids, including pelycosaurs
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Mesozoic
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Triassic
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248-213 mya
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First turtles, cycads, lizards, dinosaurs, mammals
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Jurassic
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213-145 mya
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First squids, frogs, birds, salamanders
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Cretaceous
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145-65 mya
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First flowering plants, snakes, modern fish, rise and fall of toothed birds, heyday of dinosaurs
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Cenozoic
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Tertiary
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Paleocene
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65-55.5 mya
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Diversification of mammals
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Eocene
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55.5-33.7 mya
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First marine and large terrestrial animals, horses, whales, monkeys
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Oligocene
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33.7-23.8 mya
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First grasses, apes, anthropoids
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Miocene
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23.8-5.3 mya
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First hominids
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Pliocene
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5.3-1.8 mya
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First Australopithecines
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Quaternary
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Pleistocene
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1.8 mya-8,000 ya
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Mammoths, mastodons, Neanderthals
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Holocene
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8,000 ya-present
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First modern human beings
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