The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the final period of the Mesozoic Era, following the Jurassic. During this time, the Earth experienced significant changes, including rising sea levels and the formation of new landmasses. This period is known for the dominance of dinosaurs, such as Tyrannosaurus rex and Triceratops. The Cretaceous ended with a mass extinction event, likely caused by an asteroid impact, which led to the extinction of many species, including the dinosaurs, paving the way for the rise of mammals in the Cenozoic Era.