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Earh forms; continental shields appear; fossils are rare; cyanobacteria are the most common organism.
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Geological Timescale
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Shelled marine invertebrates appear; trilobites and brachiopods are common; first vertebrates appear; atmosphere reaches modern O2-rich state.
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Echinoderms appear; brachiopods increase; trilobites decline; graptolites flourish.
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Eurypterids, land plants and animals appear.
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Age of fishes begins; amphibians appear; giant horsetails, ferns, and seed-bearing plants develop.
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Amphibians flourish; brachiopods are common in oceans; forests and swamps cover most land.
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Giant cockroaches and dragonflies are common; coal deposits form; reptiles appear.
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Pangaea comes together; mass extinctions mark the end of the Paleolozoic Era.
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Dinosaurs appear; ammonites are common; cyads and conifers are abundant; mammals appear.
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Dinosaurs are the dominant life-form; primitive birds and flying reptiles appear.
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Flowering plants and modern birds appear; mass extinctions mark the end of the Mesozoic Era.
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Age of mammals begins; first primates appear.
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The last glacial ends; complex human societies develop.
