Question: what are the three divisions of the phanerozoic eon?
Answer: The Phanerozoic, the eon of visible life, is divided into three major spans of time largely on the basis of characteristic assemblages of life-forms: the Paleozoic (541 million to 252 million years ago), Mesozoic (252 million to 66 million years ago), and Cenozoic (66 million years ago to the present) eras.