Ans. The phanerozoic eon was divided into three eras namely the Paleozoic, the Mesozoic, and the Cenozoic. The eras were named for the kind of fossils that were present. The youngest era is the Cenozoic era meaning new life. This is because fossils are similar to plants and animals that are common today. The paleozoic era is the earliest era which means ancient life. Fossil from the Paleozoic era includes plants and animals that are completely extinct. The Mesozoic era means middle life. The fossils in this era are a mixture of extinct groups and modern groups of plants and animals.