Geological time is a way of measuring the age of the Earth and its various components. It is divided into four main categories: EON, EPOCH, ERA, and AEON. An EON is the longest period of geological time, lasting hundreds of millions of years. An EPOCH is a shorter period of time, lasting millions of years. An ERA is an even shorter period of time, lasting tens of millions of years. Finally, an AEON is the shortest period of geological time, lasting only a few million years. Together, these four categories provide a comprehensive timeline for the Earth's history.