Archaean

• (n.) The earliest period in geological period, extending up to the Lower Silurian. It includes an Azoic age, previous to the appearance of life, and an Eozoic age, including the earliest forms of life. • (a.) Ancient; pertaining to the earliest period in geological history.
Found on http://thinkexist.com/dictionary/meaning/archaean/

Archaean

The Archaean is the earliest period in geological period, extending up to the Lower Silurian. It includes an Azoic age, previous to the appearance of life, and an Eozoic age, including the earliest forms of life. This is equivalent to the formerly accepted term Azoic, and to the Eozoic of Dawson.
Found on http://www.probertencyclopaedia.com/browse/HA.HTM

Archaean

The middle era of Precambrian time, spanning the period between 3.8 and 2.5 billion years ago. Life arose on Earth during the early Archaean, as indicated by the appearance of fossil bacteria in rocks thought to be about 3.5 billion years old. Its name means 'ancient.'
Found on https://www.encyclo.co.uk/local/21202

Archaean

Widely used term for the earliest era of geological time; the first part of the Precambrian Eon, spanning the interval from the formation of Earth to about 2,500 million years ago
Found on http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0006349.html
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