1) Archaean 2) Early 3) Of a geologic age 1) Archaean 2) Early 
The Archean Eon (n, also spelled Archaean; formerly Archaeozoic k, also spelled Archeozoic or Archæozoic) is a geologic eon before the Proterozoic Eon, before 2.5 Ga (billion years), or {Ma|2500}. ==Classification issues== Instead of being based on stratigraphy as all other geological ages are, the beginning of the Archean eon is defined chronome...
The oldest rocks of the Precambrian era, older than about 2,500 million years.
Geologic eon that occurred from 2500 to 3800 million years ago. During this time period, the first single-celled prokaryote organisms evolved and developed.
[adj] - (geology) used of the earliest known rocks 2. [n] - the time prior to 2,500 million years ago
archaean adjective used of the earliest known rocks
An eon of geologic time extending from about 3.9 billion years to 2.5 billion years ago.
noting or pertaining to rocks of the Archeozoic portion of the Precambrian Era.