Prehistoric time line, geologic time scale, photos, facts, maps, and more from National Geographic. Humans have walked the Earth for 190,000 ... emerged in the Cenozoic era. The planet has seen ...

3 min read At the dawn of the Paleogene—the beginning of the Cenozoic era—dinosaurs, pterosaurs, and giant marine reptiles were conspicuously absent from the face of the Earth. Rodent-size ...