A scale that measures the vast amounts of time over which geological changes occur. Divided into eons, eras, periods, and epochs. We are now in the Phanerozoic Eon that started 543 million years ago when animals began to fossilize in large numbers, the Cenozoic Era (started 65 million years ago when the dinosaurs blew out), Quaternary Period (roughly 2 million years ago, when pre-humans appeared), Holocene Epoch (10,000 years ago, when the last Ice Age ended).