Era (geology)
A geologic era is a subdivision of geologic time that divides an eon into smaller units of time. 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.
List of geological eras in Earth's evolutionary history
| Era | Time frame (Ma = million years ago) |
|---|---|
| Cenozoic | 66 million years ago to present day |
| Mesozoic | 252.17 to 66 million years ago |
| Paleozoic | 541 to 252.17 million years ago |
| Neoproterozoic | 1,000 to 541 million years ago |
| Mesoproterozoic | 1,600 to 1,000 million years ago |
| Paleoproterozoic | 2,500 to 1,600 million years ago |
| Neoarchean | 2,800 to 2,500 million years ago |
| Mesoarchean | 3,200 to 2,800 million years ago |
| Paleoarchean | 3,600 to 3,200 million years ago |
| Eoarchean | 4,000 to 3,600 million years ago |
| Hadean Eon not officially divided into eras |
Formation of Earth to 4,000 million years ago |
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