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
, 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-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, those eons have been subdivided into eras of their own.
Geologic eras are further subdivided into geologic periods.
This page was last edited on 25 February 2018, at 18:29.
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