Era (geology)

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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.

Era Time frame (Ma = million years ago)
Cenozoic 66 million years ago to present day
Mesozoic 252.2 to 66 million years ago
Paleozoic 541 to 252.2 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

See also[edit]