designating or of the geologic eon characterized by the development of the first igneous and metamorphic rocks and the first marine microorganisms; Precambrian, esp. early Precambrian
< Gr archaios, archaic
See Archean in American Heritage Dictionary 4
Of or belonging to the earlier of the two divisions of Precambrian time, from approximately 3.8 to 2.5 billion years ago, marked by an atmosphere with little free oxygen, the formation of the first rocks and oceans, and the development of unicellular life. See Table at geologic time.
Of or relating to the oldest known rocks, those of the Precambrian Eon, that are predominantly igneous in composition.