Archaean

[ ahr-kee-uh n ]
/ ɑrˈki ən /

adjective Geology.

Definition for archaean (2 of 2)

Archean

or Ar·chae·an

[ ahr-kee-uh n ]
/ ɑrˈki ən /

adjective Geology.

noting or pertaining to rocks of the Archeozoic portion of the Precambrian Era.

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. 2019

Examples from the Web for archaean

British Dictionary definitions for archaean (1 of 3)

archaean

/ (ɑːˈkɪən) /

noun

any member of the Archaea, a domain of prokaryotic microorganisms, distinguished from bacteria on molecular phylogenetic grounds and often found in hostile environments, such as volcanic vents and hot springs

British Dictionary definitions for archaean (2 of 3)

Archaean

esp US Archean

/ (ɑːˈkiːən) /

adjective

of or relating to the highly metamorphosed rocks formed in the early Precambrian era
the earlier of two divisions of the Precambrian era, during which the earliest forms of life are assumed to have appeared

Compare Proterozoic

British Dictionary definitions for archaean (3 of 3)

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

Science definitions for archaean (1 of 2)

Archaean

[ är-kēən ]

Another spelling of Archean.

Science definitions for archaean (2 of 2)

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.