1. Hadean eon formation of the solar system
2. Archean eon buildup of oxygen; first eukaryotes
3. Proterozoic eon largest mass extinction in Earth's history
4. Phanerozoic eon time of the dinosaurs
5. Paleozoic era sometimes called "Age of Mammals"
6. Mesozoic era current eon in Earth's history
7. Cenozoic era toxic atmosphere; first bacteria