Archaea

n. organisms found in the oldest Precambrian rocks, i.e. rocks of the Archaean era.

Archaean

a. appl. the earlier eon of the Precambrian, ending at about 2500 million years ago.

Archaebacteria

n. plu. class of prokaryotic microorganisms forming the division Mendosicutes, including extreme thermophiles, extreme halophiles and methanogens (methane producers). Typically found in extreme environments, e.g. hot springs, salt lakes. They differ in many ways from other bacteria, e.g. in the structure of their cell walls and membrane lipids and posession of introns in some genes, and are thought to represent a quite separate group from the true bacteria or eubacteria.

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