Geological period is a unit of time in the geologic time scale that is used to describe the history of Earth. The AZOIC period is the earliest period of Earth's history, before the emergence of life. The EOCENE period is the second EPOCH of the Paleogene period and lasted from 56 to 33.9 million years ago. An ERA is a subdivision of geologic time that is longer than an EPOCH but shorter than an EON. The CAMBRIAN period is the first period of the Paleozoic ERA and lasted from 541 to 485.4 million years ago. The Miocene period is the second EPOCH of the Neogene period and lasted from 23.03 to 5.333 million years ago. An EON is the largest division of geologic time and is divided into eras. An AEON is a very long period of time, usually millions of years. The Triassic period is the first period of the Mesozoic ERA and lasted from 252.17 to 201.3 million years ago. An EPOCH is a subdivision of geologic time that is longer than an AGE but shorter than a period. The Permian period is the last period of the Paleozoic ERA and lasted from 299.0 to 252.17 million years ago. Dyas is an informal term for the Jurassic period, which lasted from 199.6 to 145.5 million years ago. The Ice AGE is a period of colder global temperatures that began around 2.58 million years ago and lasted until about 11, 700 years ago. The Neocene period is the third EPOCH of the Neogene period and lasted from 5.333 to 2.58 million years ago.