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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-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.

List of geological eras in Earth's history[edit]

"Era Time frame ("Ma = million years ago)
"Cenozoic 66 million years ago to present
"Mesozoic 251.902 to 66 "million years ago
"Paleozoic 541 to 251.902 "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]

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