The term GEOLOGIC PERIOD is used to describe the timeline of Earth's history. It is divided into smaller units such as AGE (3 letters), EPOCH (5 letters), ERA (3 letters), EON (3 letters), AEON (4 letters), LIAS (4 letters), ICEAGE (6 letters) and TRIASSIC (8 letters). An AGE is the smallest unit of geologic time, lasting millions of years. An EPOCH is a subdivision of an AGE, lasting thousands of years. An ERA is a subdivision of an EPOCH, lasting tens of millions of years. An EON is the largest unit of geologic time, lasting hundreds of millions of years. An AEON is a subdivision of an EON, lasting billions of years. The LIAS is an EPOCH in the Jurassic period, while the ICEAGE is an EPOCH in the Quaternary period. The TRIASSIC is an ERA in the Mesozoic period.