The term for the period in history when dinosaurs roamed the Earth is called the Mesozoic Era. This era lasted from about 252 to 66 million years ago and is divided into three periods: the Triassic, Jurassic, and Cretaceous. During the Mesozoic, dinosaurs became the dominant terrestrial vertebrates, evolving into diverse species. It also witnessed the emergence of other significant life forms, including mammals and birds. The Mesozoic Era ended with a mass extinction event, likely caused by an asteroid impact, which led to the extinction of the dinosaurs and paved the way for the rise of mammals in the ensuing Cenozoic Era.