"of the earliest geological age," 1872, from Greek arkhaios "ancient," from arkhe "beginning" (see archon).

geological time period between 3.8 billion years ago and 2.5 billion years ago.

kingdom made up of unicellular prokaryotic cells that can survive in extreme environments. archeology (archaeology) -

(adj) of or relating to the earliest known rocks formed during the Precambrian Eon

The oldest geological era - Older than 2,400 million years.

<geology> 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. This is equivalent to the formerly accepted term Azoic, and to the Eozoic of Dawson. (01 Mar 1998)

(geology) of, or relating to the geologic eon from about 3,800 to 2,500 million years ago; comprises the Eoarchean, Paleoarchean, Mesoarchean and Neoarchean eras; marked by an atmosphere with little [..]