The Cretaceous period is a geological period that lasted from approximately 145 to 66 million years ago. It is known for being the last period of the Mesozoic Era and the age of the dinosaurs. The Cretaceous period is characterized by the diversification of various groups of organisms, including flowering plants, reptiles, and marine life. It ended with a mass extinction event, which led to the extinction of the non-avian dinosaurs and the rise of mammals.