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Prehistoric Time Line

Prehistoric time line, geologic time scale, photos, facts, maps, and more from National Geographic.

Humans have walked the Earth for 190,000 years, a mere blip in Earth's 4.5-billion-year history. A lot has happened in that time. Earth formed and oxygen levels rose in the foundational years of the Precambrian. The productive Paleozoic era gave rise to hard-shelled organisms, vertebrates, amphibians, and reptiles. Dinosaurs ruled the Earth in the mighty Mesozoic. And 64 million years after dinosaurs went extinct, modern humans emerged in the Cenozoic era. The planet has seen an incredible series of changes—discover them for yourself.

Dinosaurs 101 They ruled the Earth for more than 160 million years, but much about how dinosaurs lived and died remains a mystery. See what we know and don't know about the age of dinos.