The term 'Major Divisions of Geological Time' refers to the four ERAS of geologic time: the Precambrian, Paleozoic, Mesozoic, and Cenozoic. The Precambrian era is the oldest, spanning from 4.6 billion years ago to 541 million years ago. The Paleozoic era followed, lasting from 541 million years ago to 252 million years ago. The Mesozoic era was next, lasting from 252 million years ago to 66 million years ago. Finally, the Cenozoic era began 66 million years ago and continues to the present day.