eon

Eon, often spelled aeon, is a term used to denote a very long period of time. In everyday language it conveys an immeasurably long interval, while in formal contexts it can refer to a defined unit of geological or cosmological time. The word originates from the Greek aion, meaning an age or lifetime.

In geology, an eon is the largest division of geological time. Eons span hundreds of millions to billions of years and are subdivided into eras, periods, epochs, and ages. The current framework recognizes four eons: the Hadean, Archean, and Proterozoic eons, which together form the Precambrian, and the Phanerozoic eon, which began about 541 million years ago and continues today. The Phanerozoic is divided into the Paleozoic, Mesozoic, and Cenozoic eras. Boundaries between eons are selected based on major changes in Earth’s geology and biota, such as mass extinctions and the appearance of multicellular life.

In popular culture and industry, "Eon" or related spellings appear in several proper names. Eon Productions is a British film production company best known for producing the James Bond film series. E.ON SE is a German multinational energy company that operates in electricity and gas markets across Europe. The capitalization and spelling vary by organization and language, with "aeon" more common in British English and "eon" in American usage when used as a generic term.

Beyond these uses, the term is employed in science fiction and philosophy to describe extremely long cosmological timescales, sometimes used to convey vast distances or durations beyond human experience.