Geologic time scale

The geologic time scale was used by geologists and other scientists to map the history of Earth. It was based on volcanic rock formations, fossil analysis, population growth, and climate and oceanic changes. Cataclysmic events such as continental drift, formation of polar ice caps, the mass extinction of dinosaurs and plants, and Ice Ages were all marked on the geologic time scale. (PROSE: Exodus Code)

Behind the scenes
While many geologic eras are mentioned in Doctor Who stories, their exact order is rarely outlined and years mentioned are sometimes contradictory. From oldest to most recent, the relevant eras geologic time scale are:

(Eras are divided into periods, which are divided into epochs.)

Pre-Cambrian

Palaeozoic Mesozoic Cenozoic
 * Cambrian
 * Ordovician
 * Silurian
 * Devonian
 * Carboniferous
 * Permian
 * Triassic
 * Jurassic
 * Cretaceous
 * Palaeogene
 * Palaeocene
 * Eocene
 * Oligocene
 * Neogene
 * Miocene
 * Pliocene
 * Quaternary
 * Pleistocene
 * Holocene
 * Anthropocene (unofficial)