The geological time scale is divided into eons, eras, periods, epochs, and ages. Each period marks significant evolutionary or environmental changes.
- Eons: Hadean (4.6-3.8 billion years ago), Archean (3.8-2.5 billion years ago), Proterozoic (2.5-0.541 billion years ago), Phanerozoic (0.541 billion years to present).
- Eras: Paleozoic, Mesozoic, and Cenozoic.
Major events include:
- Pangaea formation in the late Paleozoic.
- The breakup of Pangaea into Laurasia and Gondwana during the Jurassic.
- The rise of mammals in the Triassic-Jurassic boundary, leading to the dominance of dinosaurs by the Mesozoic era.
- The Cretaceous-Paleogene extinction event that wiped out non-avian dinosaurs 65 million years ago.
Pro tip: The Precambrian is often considered a single eon due to lack of clear stratigraphic evidence for its division into eras and periods.