• synonyms


or Ar·chae·an

[ahr-kee-uh n]
adjective Geology.
  1. noting or pertaining to rocks of the Archeozoic portion of the Precambrian Era.
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Origin of Archean

1870–75; < Greek archaî(os) ancient (see archaeo-) + -an
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for archean

Historical Examples of archean

  • It is the home of the Archean granite, and its basins are of a fathomless dust.

    Whispering Smith

    Frank H. Spearman

  • The period following on after Archean time is called, by geologists, Paleozoic time.

  • These areas of Archean rocks were doubtless once continuous.

  • This vast period of time, which includes the beginning, is known among geologists as Archean time.

  • At the bottom of the sea were the Archean or igneous rocks, the oldest formation known to geology.

British Dictionary definitions for archean


  1. a variant spelling (esp US) of Archaean
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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

archean in Science


  1. 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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.