Question - Dinosaurs first appear in the geological record in rocks from about 215 Ma and then became extinct 65 Ma.

Dinosaurs first appear in the geological record in rocks from about 215 Ma and then became extinct 65 Ma. For what proportion (%) of geological time did dinosaurs exist?

ANSWER:

215 – 65 = 150 Ma. Since the age of the Earth is 4570 Ma, this represents 150/4,570 = 0.033 or 3.3% of geological time.