A geologic era is a subdivision of geologic time that divides an Eon into smaller buckets. The Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic represent the major stages in the macroscopic fossil record. These eras are separated by catastrophic extinction boundaries, the P-T boundary between the Paleozoic and the Mesozoic and the K-T boundary between the Mesozoic and the Cenozoic. There is evidence that catastrophic meteorite impacts played a role in demarcating the differences between the eras.
The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. More recently, however, those eons have been subdivided into eras of their own.
| Era | Time frame (Ma = million years ago) |
|---|---|
| Cenozoic | 66 Ma to present day |
| Mesozoic | 252 Ma–66 Ma |
| Paleozoic | 542 Ma–252 Ma |
| Neoproterozoic | 1000 Ma–542 Ma |
| Mesoproterozoic | 1600 Ma–1000 Ma |
| Paleoproterozoic | 2500 Ma–1600 Ma |
| Neoarchean | 2800 Ma–2500 Ma |
| Mesoarchean | 3200 Ma–2800 Ma |
| Paleoarchean | 3600 Ma–3200 Ma |
| Eoarchean | 3800 Ma (unofficial)–3600 Ma |
| Hadean Eon not officially divided into eras |
Formation of Earth to 3800 Ma |