A geologists who divides all time since the formation of the earliest known rocks (about four billion years ago) into four major divisions: Precambrian, Paleozoic, Mesozoic, and Cenozoic eras: A historical geologis maintains that each era, except the Cenozoic, ended with profound changes in the disposition of the Earth's continents and mountains and was characterized by the emergence of new forms of life.

Broad cyclical patterns, which run through all historical geology, include a period of mountain and continent building followed by one of erosion, and then by a new period of elevation.