An epoch in geology is a part of a period. Thus the Cainozoic era is now divided into three periods, the Palaeogene, the Neogene and the Quaternary. These are finally broken down into these epochs: Palaeocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene and Holocene.
The Tertiary, now not used ('deprecated'), included the Palaeogene and Neogene. That is why the last period is called the Quarternary, and there was a big debate about that, too. These decisions are made by the International Union of Geological Sciences (IUGS). This organisation runs an International Commission on Stratigraphy, which decides how we should name geological strata and stages. They describe their work as follows:
- "[Our] primary objective is to precisely define global units (systems, series, and stages) of the International Chronostratigraphic Chart... [These] are the basis for the units (periods, epochs, and age) of the International Geologic Time Scale."
- International Commission on Stratigraphy International Commission on Stratigraphy There are alternate spellings for some terms: the prefix 'Palaeo' is written 'Paleo' in American English. both versions are correct. 'Cainozoic' may be spelled 'Cenozoic'. Archived 14 February 2012 at WebCite
- International Committee on Stratigraphy International Commission on Stratigraphy Archived 17 January 2010 at WebCite