Geological ages of the Earth from its origins (some 4,500 million years ago) up to the present.

There are four eons: Hadean, Archeozoic, Proterozoic, Phanerozoic, whose names refer to the evolution of life on earth. The last eon, the Phanerozoic, we know best due to the existence of visible fossils and is divided in the three eras: Paleozoic, Mesozoic and Cenozoic. The eras are in turn subdivided into periods. The Cambrian is the first period of the Paleozoic (all prior time is called Precambrian).