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|
not officially divided into eras
|Formation of Earth to 3800 Ma|