archæan

Century Dictionary and Cyclopedia

1. Of or relating to the oldest period of geological time: a name proposed by J. D. Dana, and now generally adopted, for a series of crystalline schists and massive rocks lying underneath the most ancient fossiliferous stratified formations. This series is still called by some writers azoic, because thus far it has not been found to contain any traces of life. It also includes an undetermined portion of the rocks formerly designated as primitive, and by some writers is vaguely used to indicate crystalline rocks of uncertain and often quite recent age. See azoic and primitive.

GNU Webster's 1913

1. adj. Ancient; pertaining to the earliest period in geological history.
2. n. (Geol.) 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.