How Long Is an Eon?
Last Updated Mar 29, 2020 6:35:40 PM ET
Although astronomers and geologists use the word "eon" to mean 1 billion years, it is more commonly used to refer to any long, indefinite period of time. Like the words "age," "epoch" and "era," it does not refer to a set number of years.
In ancient Greece, the word "aion" meant an infinitely long time or an eternity. Plato used the word to denote the eternal ideas that lay behind the perceived world. Geologists divide the history of the Earth into four geologic eons. The latest, called the Phanerozoic Eon, began 540 million years ago and continues into the present day.
More From Reference

What Is an Ex-Dividend Date, and How Does It Affect Your Stocks?

What Is the Difference Between Salary and Wages?

How Many Minutes of Daylight Do We Gain Each Day? And Other Daylight Saving Time Facts

Understanding SSI: Supplemental Security Income Basics for New Applicants

What Can the History of Polio Teach Us About the Coronavirus Pandemic?

How to Use a Personal Loan Calculator