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Older of the two divisions of Precambrian time. The Archean begins with the formation of the Earth's crust 4 billion years ago and extends to 2.5 billion years ago, up to the start of the Proterozoic Eon, the second division of the Precambrian Period. The earliest and most-primitive forms of life (bacteria and cyanobacteria) originated more than 3.5 billion years ago in the middle of the Archean Eon (the Archean's alternative name, Archeozoic, means ancient life).
Variants of ARCHEAN EON
Archean Eon or Archaean Eon or Archeozoic Eon
This entry comes from Encyclopædia Britannica Concise. For the full entry on Archean Eon, visit Britannica.com.
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