Ans. The phanerozoic eon was divided into three eras namely the Paleozoic, the Mesozoic, and the Cenozoic. The climate of the Earth changed multiple times during the Phanerozoic Eon. At the end of the Precambrian period, much of the planets were covered with glaciers. At the beginning of the Phanerozoic Eon, the climate was warm and humid. Since then Earth's climate has gone through four cycles of frigid areas and warm tropical seas. Some of the organisms survived in the changing climate. Others go extinct when the climate changes too much.