Final answer:
An eon is a unit of geological time that can be hundreds of millions to billions of years long and is used to describe some of the largest divisions in Earth's history.
Step-by-step explanation:
An eon is a very long span of time which is used in geology to describe the largest divisions of the geological time scale. Geologic time is divided into eons, which are further subdivided into eras, periods, epochs, and ages. In the context of Earth's history, eons are often hundreds of millions to billions of years long. However, there isn’t a set number of years that universally defines an eon. The lengths of eons can vary.
The Earth has been through several eons in its history. The Precambrian super eon, for example, comprises the Hadean, Archean, and Proterozoic eons and covers approximately 4 billion years of Earth's history. But eons can be longer or shorter than this. When it comes to the age of the universe, which is about 13.8 billion years, it spans multiple eons.