A Short History of Nearly Everything

by Bill Bryson

Originally, geological history was divided into four spans of time: primary, secondary, tertiary and quaternary. The system was too neat to last, and soon geologists were contributing additional divisions while eliminating others. Primary and secondary fell out of use altogether, while quaternary was discarded by some but kept by others. Today only tertiary remains as a common designation everywhere, even though it no longer represents a third period of anything. Lyell, in his Principles, introduced additional units known as epochs or series to cover the period since the age of the dinosaurs, among them Pleistocene (‘most recent’), Pliocene (‘more recent’), Miocene (‘moderately recent’) and the rather endearingly vague Oligocene (‘but a little recent’). Lyell originally intended to employ ‘-synchronous’ for his endings25, giving us such crunchy designations as Meiosynchronous and Pleiosynchronous. The Reverend William Whewell, an influential man, objected on etymological grounds and suggested instead an ‘-eous’ pattern, producing Meioneous, Pleioneous and so on. The ‘-cene’ terminations were thus something of a compromise. Nowadays, and speaking very generally, geological time is divided first into four great chunks known as eras: Precambrian, Palaeozoic (from the Greek meaning ‘old life’), Mesozoic (‘middle life’) and Cenozoic (‘recent life’). These four eras are further divided into anywhere from a dozen to twenty subgroups, usually called periods though sometimes known ...

Geological division of Historical time