The Phanerozoic covers the last 570 Ma of Earth history, made up of three Eras, the Palaeozoic (570 to 225Ma), Mesozoic (225 to 65Ma) and Cenozoic (65Ma to present) (see appendix). Each Era is divided up into different Periods, and each Period is divided into a number of Epochs. The most recent Period of the geologic record is the Quaternary (considered in section 5.3), comprising the Pleistocene (2Ma to 10Ka) (see section 5.3.1) and Holocene (10Ka to present) (see section 5.3.2). In this section, only pre-Quaternary climates will be considered.
The most likely candidates for long term climate forcing include those associated with continental drift, orogeny (section 2.6.1) and epeirogeny (section 2.6.2). The growth of mountain ranges may affect atmospheric circulation patterns; movement of land masses into high latitude region may initiate strong ice-albedo feedbacks; variations in the rate of sea-floor spreading may alter ocean bathymetry and global carbon dioxide emissions.
The Phanerozoic has witnessed the evolution of a major tectonic cycle, involving the coming together of land masses to form a single super-continent known as Pangea (about 220Ma), followed by its disintegration, resulting in the configuration of continents that exist today. Associated with this continental drift were variations in tectonic activity and ocean-floor spreading, with subsequent fluctuations in ocean bathymetry and global sea level (Vail et al., 1977). Figure 5.1 shows how global sea level has varied during the course of the Phanerozoic.