Eén

Eón, in the context of time scales, is the largest division of geological time. The term derives from the Greek aion, meaning an age or an indefinite life span. In geology and earth science, an eón spans hundreds of millions to billions of years and contains multiple eras.

Geologic eons are commonly listed as the Hadean, Archean, Proterozoic, and Phanerozoic. The Hadean lasted from about 4.6 to 4.0 billion years ago; the Archean from roughly 4.0 to 2.5 billion years ago; the Proterozoic from about 2.5 billion to 541 million years ago; and the Phanerozoic from about 541 million years ago to the present. The Phanerozoic is the eon during which abundant complex life has existed and is further divided into the Paleozoic, Mesozoic, and Cenozoic eras.

Outside geology, eon is used in cosmology and everyday language to denote an extremely long period, often on the order of billions of years. The term is synonymous with aeon in British English and often appears in religious or philosophical contexts as well, where aeon can refer to a divine age or emanation in certain traditions.

In summary, an eón is the broadest formal time unit in geology, defining the major expanse of Earth’s history, while also serving as a general term for long durations in science and culture.