Geologic Time Scale: Eons and Eras
| Eon | Era | Dates (m.y.) |
| Phanerozoic | Cenozoic | 66-0 |
| Mesozoic | 251-66 | |
| Paleozoic | 542-251 | |
| Proterozoic | Neoproterozoic | 1000-542 |
| Mesoproterozoic | 1600-1000 | |
| Paleoproterozoic | 2500-1600 | |
| Archean | Neoarchean | 2800-2500 |
| Mesoarchean | 3200-2800 | |
| Paleoarchean | 3600-3200 | |
| Eoarchean | 4600-3600 |
All of geologic time, from the Earth's origin about 4600 million years ago to today, is divided into three eons. The first two eons, Archean and Proterozoic, and their seven eras are together informally referred to as Precambrian time. Read summaries of the Archean Eon and the Proterozoic Eon.
The eras of the Proterozoic and Phanerozoic eons are each further divided into periods, shown in this geologic time scale.
The periods of the three Phanerozoic eras are divided in turn into epochs. (See the Phanerozoic epochs listed together.) Epochs are subdivided into ages. Because there are so many ages, they are presented separately for the Paleozoic Era, the Mesozoic Era and the Cenozoic Era.
The dates and colors shown on this table were specified by the International Commission on Stratigraphy in 2004. Colors are used to indicate the age of rocks on geologic maps. There are two major color standards, the international standard and the U.S. Geological Survey standard. (All of the geologic time scales here are made using the USGS standard.)
