The document discusses the different periods of the age of dinosaurs. It was divided into three periods - the Triassic, Jurassic, and Cretaceous periods. The Triassic period lasted from 251 to 201 million years ago and saw the rise of the earliest dinosaurs. The Jurassic period occurred between 199.6 to 145.5 million years ago and was characterized by warm temperatures and abundant plant and animal life. The Cretaceous period lasted from 145 to 66 million years ago and ended with a meteor impact that caused the extinction of the dinosaurs.