What are the divisions of the geologic time scale?
From biggest to smallest: Eons - Eras - Periods - Epochs
Their is two eons: Cryptozoic (which means hidden life) and often called Precambrian (meaning the time before the Cambrian era)
and Phanerozoic (which means visible life) they both cover the 4.6 billion years of earth's history ( the Phanerozoic started 542 million years ago).
Then the two eons are divided into smaller time units called eras and eras are divided into periods and periods into epochs.