Paleozoic

The Greek root zo- means "life," so names such as Paleozoic were invented to refer to a period in the development of animal life. For geologists, the Paleozoic era is followed by the Mesozoic (meso- meaning "middle"), which is followed by the Cenozoic (ceno- meaning "recent"). Eras are huge stretches of time; geologists break eras down into smaller "periods" and "epochs." Thus, the Paleozoic ends with the Permian period, the Mesozoic ends with the Upper Cretaceous epoch, and the Cenozoic ends with the Holocene epoch—the epoch in which we are living. The Paleozoic era produced the first fish, the first land plants, the first insects, and the first amphibians and reptiles; the dinosaurs, birds, and mammals had to wait for the Mesozoic.