In the geological time frame, there are 3 Eras: Paleozoic, Mesozoic, and the third one is?

Question

Hint:

1. Paleozoic Era = 543 million years ago (starting with the Cambrian period - shellfish, trilobites)
2. Mesozoic Era = 248 million years ago (starting with the Triassic period - dinosaurs, mammals)
3. _______ Era = 65 million years ago (starting with the Tertiary period - mass extinction)