Period of time determined to occur just before 2.5 thousand million years back.
the time from 1.5 billion to 5 billion years back; the full time if the planet's crust formed; an occasion whenever only unicellular organisms as well as the first forms of life are present.
The Archæozoic eon.
enough time from 3,800 million many years to 2,500 million years ago; earth's crust created; unicellular organisms tend to be first kinds of life
In geology, having mention of the earliest life-forms based in the rocks: a phrase introduced by Le Conte and employed by Dana to designate a hypothetical division or eon of Archæan time contradistinguished from the Azoic eon.