The document summarizes the geologic time scale which divides Earth's history into sections called eons, eras, periods, and epochs based on major changes. It describes several important periods including the Precambrian, Paleozoic, Mesozoic, and Cenozoic eras. The Paleozoic era saw the first appearance of hard-shelled animals and plants colonizing land. It ended in a mass extinction event. The Mesozoic era was dominated by reptiles such as dinosaurs, until another mass extinction wiped them out. The current Cenozoic era is when mammals and eventually humans evolved.

1. Geologic Time Scale

5. Precambrian Time

11. Mesozoic Era

16. Cenozoic Era