(geology), a subdivision of the general stratigraphic scale, subordinate to the eonothem and itself subdivided into stratigraphic systems. In the Russian geological literature, the erathem was usually called group. In 1966, the American geologist H. Hedberg suggested the term “erathem,” which was adopted in the USSR in 1976. The time interval during which an erathem forms corresponds to an era. (See alsoSTRATIGRAPHY.)