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

With the passing of the Archean, the earth had not yet settled into the perfectly balanced sphere which Nature destined it to be.
The Book of the National Parks Robert Sterling Yard

At the bottom of the sea were the Archean or igneous rocks, the oldest formation known to geology.
Baraboo, Dells, and Devil’s Lake Region H. E. Cole

Yet either is inconsiderable against the total lapse of time even from the Archean’s close till now.
The Book of the National Parks Robert Sterling Yard

It is to this lowermost gneissic group that the term “Archean” may be conveniently limited.
Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 Various

This vast period of time, which includes the beginning, is known among geologists as Archean time.
The Prehistoric World E. A. Allen

Australia is essentially the fragment of a great plateau land of Archean rocks.
Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 8 Various

The period following on after Archean time is called, by geologists, Paleozoic time.
The Prehistoric World E. A. Allen

The breaking up of the old Archean foundation block began in Cambrian and Ordovician times.
Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 8 Various

The definite history of the earth begins with the close of the dim Archean era.
The Book of the National Parks Robert Sterling Yard

At one time these rocks were regarded as Archean gneisses of a special type.
Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 3 Various

a variant spelling (esp US) of Archaean
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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