(Geology) Used of the earliest known rocks; SYN. archaean.
1. Of, relating to, or being the earliest eon of geological history or the corresponding system of rocks — see GEOLOGIC TIME table.
2. PRECAMBRIAN.

Or Archeozoic; The earliest eon of geological time; the first part of the Precambrian, from the formation of Earth up to about 2,500 million years ago. It was a time when no life existed, and with every new discovery of ancient life its upper boundary is being pushed further back.