Triassic Period, a division of geologic time that began about 240,000,000 years ago and lasted about 35,000,000 years. It is the earliest period in the Mesozoic Era. The Triassic Period is named for a three-layered rock formation in northern Germany that was formed during this period. The bottom layer is primarily red sandstone, the middle layer limestone, and the upper layer a combination of red sandstone and shale. In North America, rocks formed from sediments deposited during the Triassic Period are found in Nova Scotia and Connecticut, along the Piedmont in New Jersey southward into South Carolina, and in the foothills of the Rocky Mountains.

Geologists believe that at the beginning of the period, there was a single landmass, which they call Pangaea. By the end of the period, Pangaea had begun to break apart into sections. The sections have continued to move slowly in relation to each other, forming the continents as they appear today. During the Triassic Period, reptiles were the dominant form of animal life. Among the fossils found in Triassic rocks are those of the first known dinosaurs and crocodiles. Also found are fossils of the first known mammals.