Archean

or Ar·chae·an

[ ahr-kee-uhn ]

noun

1. 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

1. of or relating to this eon.

Archean

/ ɑːˈkiːən /

adjective

1. See Archaean
   a variant spelling (esp US) of Archaean

Archean

/ är-kē′ən /

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.
2. See Chart at geologic time

Word History and Origins

Origin of Archean¹

First recorded in 1870–75; from Greek archaî(os) “ancient” + -an adjective suffix; archaeo-, -an

Example Sentences

From self-replicating molecules in Archean seas, to eyeless fish in the Cambrian deep, to mammals scurrying from dinosaurs in the dark, and then, finally, improbably, ourselves—evolution shaped us.

From Singularity Hub 

It’s possible, Byrne says, that Venus could be an analog for studying what things were like billions of years ago during Earth’s Archean period.

From Popular-Science

First they analyzed Archean rocks collected in the Isua region in western Greenland.

From Quanta Magazine

In the geological history of France there have been two great periods of folding since Archean times.

From Project Gutenberg

Two important ones, however—namely, Archean and Algonkian—are of American birth.

From Project Gutenberg

These occur widely throughout North America, and in formations of all ages subsequent to the Archean.

From Project Gutenberg

A theory held by many refers the ultimate source of the iron to the igneous rocks of the Archean.

From Project Gutenberg

With a few exceptions, to be noted later, all the rocks are of pre-Cambrian, perhaps in part of Archean age.

From Project Gutenberg