Geologic period

A geologic period is the third largest unit of time for the geologic time scale (Figure 1). Geologic periods are also referred to as "systems" (the chronostratigraphic name) or simply "periods". Periods tend to be 30 to 80 million years in length. Periods are subsections of longer eras and consist of groups of shorter epochs. Period names have a range of endings but the most common suffixes are "-an", "-ic", and "-ous". [1]

Currently the periods are:[1]

Figure 1. The ICS Chronostratigraphic Chart[2]

For Further Reading


  1. 1.0 1.1 International Commission on Stratigraphy."Chapter 9. Chronostratigraphic units" Accessed Nov.12, 2018 [Online]. Available:
  2. International Commission on Stratigraphy."International Chronostratigraphic Chart v2018" Accessed Nov.8, 2018 [Online]. Available: