Long periods of time can be referred to in a variety of ways. EPOCHS (6 letters) are a unit of geological time that is longer than an era and shorter than a period. EONS (4 letters) are the longest unit of geological time, lasting millions of years. ERAS (4 letters) are a unit of geological time that is longer than an age and shorter than an epoch. Aeons (5 letters) are an indefinite and very long period of time. AGES (4 letters) are a unit of geological time that is longer than a period and shorter than an era. All of these terms refer to long periods of time, and can be used to describe the history of the Earth.