Archaean



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

This place is about five hundred yards west of the bridge in an alcove in the Archaean Rock which forms the Canyon wall.
I Married a Ranger Dama Margaret Smith

Directly or indirectly, the fish is a descendant of some Archaean Annelid.
The Story of Evolution Joseph McCabe

Their lithological characteristics and the total absence of all organic remains point to the Archaean period.
Encyclopaedia Britannica, 11th Edition, Volume 17, Slice 4 Various

The Archaean rocks still solidly underlie the lowest depth he has ever reached.
The Story of Evolution Joseph McCabe

It was laid down close to the igneous Archaean rocks when Mother Earth was in her girlhood and water first began to flow.
Among the Forces Henry White Warren

As we have no recognisable remains of the animals and plants of the earliest age, we will not linger over the Archaean rocks.
The Story of Evolution Joseph McCabe

Again we must refrain from following in detail the development of this new world of life which branches off in the Archaean ocean.
The Story of Evolution Joseph McCabe

The evidence suggests that both the free-moving and the stalked Echinoderms descend from a common stalked Archaean ancestor.
The Story of Evolution Joseph McCabe

The last and most important line that led upward from the chaos of Archaean worms is that of the Arthropods.
The Story of Evolution Joseph McCabe

Now it would be natural enough to suppose that those fossils which occur at the bottom, or next to the Archaean, are the oldest.
Illogical Geology George McCready Price

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
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
adjective
a variant spelling (esp US) of Archaean
adj.

“of the earliest geological age,” 1872, from Greek arkhaios “ancient,” from arkhe “beginning” (see archon).
Archaean
(är-kē’ən)
Another spelling of Archean.
Archean
(är-kē’ən)
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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