The Cretaceous period was a time in Earth's history that lasted from about 145 to 66 million years ago. It is known for being the last period of the Mesozoic Era, often called the "Age of Dinosaurs." During this time, many types of dinosaurs, like the famous Tyrannosaurus rex and Triceratops, roamed the planet. The climate was warm, and there were vast oceans filled with marine life. At the end of the Cretaceous period, a massive extinction event occurred, likely caused by a giant asteroid impact. This event led to the disappearance of about 75% of all species, including the dinosaurs. The end of the Cretaceous marked the beginning of the **Cenozoic Era