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Archean

or Ar·chae·an

[ ahr-kee-uhn ]
/ ɑrˈki ən /
Geology
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noun
the Precambrian eon that preceded the Proterozoic and during which the earliest datable rocks were formed and from which the oldest known fossil forms, including cyanobacteria, have been recovered.
adjective
of or relating to this eon.
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Origin of Archean

First recorded in 1870–75; from Greek archaî(os) “ancient” + -an adjective suffix; see archaeo-, -an
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

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British Dictionary definitions for Archean

Archean
/ (ɑːˈkiːən) /

adjective
a variant spelling (esp US) of Archaean
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for Archean

Archean
[ är-kēən ]

The earlier of the two divisions of the Precambrian Eon, from about 3.8 to 2.5 billion years ago. During this time the Earth had a reducing atmosphere consisting primarily of methane, ammonia, and other gases that would be toxic to most modern life forms. There was little free oxygen. Rocks from the earliest part of the Archean are predominantly volcanic and are similar to pillow basalts, suggesting that they formed underwater. Rocks from the later part of the Archean appear to have formed on continents. It is believed that about 70% of the continental masses formed during this time. Fossils preserved in rocks from this period of time include remains of cyanobacteria, the first single-celled forms of life. These organisms are preserved in the form of stromatolites and oncolites. See Chart at geologic time.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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