Geological time is commonly divided into four major eras: the Precambrian, Palaeozoic, Mesozoic, and Cenozoic. Each era represents significant phases in Earth's history, with the names reflecting the evolution of life. The Precambrian period covers the formation of the Earth and the earliest forms of life, while the subsequent eras showcase the development and diversification of more complex organisms.

Furthermore, these eras are broken down into numerous subgroups, typically ranging from twelve to twenty, which allow for a more detailed understanding of geological events and biological progress over time. This structured division helps scientists study the planet’s history and the evolution of life in a systematic way.