Geologic Fact One:

        Scientists break the geologic time scale into eons, eras, periods, and epochs. There's the Precambrian Time, the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era.

        Dinosaurs lived during the Mesozoic Era. However, the extinction event that destroyed the dinosaurs was not the largest in all geologic history. The largest extinction was at the end of the Permian Period of the Paleozoic Era, 252 million years ago. Most scientists speculate that volcanic eruptions were a major source of this phenomenon.