Note 5 — THE ROCKS AND THEIR HISTORY
Reading edition
Geologic time is divided into four Eras which are designated from oldest to youngest: Precambrian, Paleozoic, Mesozoic, and Cenozoic. Each of these Eras is divided into geologic periods of time. The Devonian Period is in about the middle of the Paleozoic Era and began some 330 million years ago and ended approximately 290 million years ago (see Geologic Time Scale, Fig. 14).