Geological time periods are divisions of the Earth's history that are used to categorize and study the evolution of the planet. The most commonly used divisions are EON, EPOCH, AEON, ERA, stade, and neocene. An EON is the longest division of geological time, lasting hundreds of millions of years. An EPOCH is a shorter division of geological time, lasting millions of years. An AEON is an even shorter division of geological time, lasting tens of millions of years. An ERA is a shorter division of geological time, lasting millions of years. A stade is an even shorter division of geological time, lasting thousands of years. Finally, the neocene is the shortest division of geological time, lasting thousands of years.