Aeons are vast periods of time in the geological and cosmological scales, often spanning millions or even billions of years. In geology, an aeon is the largest division of geological time, which is further divided into eras, periods, and epochs. The Earth has four main aeons: the Hadean, Archean, Proterozoic, and Phanerozoic, each marked by significant events in the planet's history. In cosmology, aeons can refer to the long timeframes associated with the universe's evolution. The concept is often used in discussions about the Big Bang and the eventual fate of the universe. Understanding aeons helps scientists study the Earth's history and the universe's development over time.