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 (meaning "old life", "middle life" and "recent life") that 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-Pg 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, the Archean and Proterozoic eons have been subdivided into eras of their own.
Geologic eras are further subdivided into geologic periods, although the Archean eras have yet to be subdivided in this way.
List of geological eras in Earth's history
|Eon||Era||Time frame (Ma = million years ago)|
|Phanerozoic||Cenozoic||66 million years ago to present|
|Mesozoic||251.902 to 66 million years ago|
|Paleozoic||541 to 251.902 million years ago|
|Proterozoic||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|
|Archean||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 (unofficial)||not officially divided into eras||Formation of Earth to 4,000 million years ago|
- "Chapter 9. Chronostratigraphic units". Stratigraphic guide. International Commission on Stratigraphy. Retrieved 2 August 2018.
- Erwin D.H. (1994). "The Permo–Triassic Extinction" (PDF). Nature. 367: 231–236.
- International Commission on Stratigraphy. "International Chronostratigraphic Chart v2018/07" (PDF). Retrieved 2 August 2018.