active migration of sand dunes polished appearance of rock surfaces marine fossils found in mountains bones of animals found on the ground
I gave my students this multiple choice question: Which of these provides the best evidence that the environment of Earth has changed over millions of years?

Only one answer is correct among these 4 choices:
- active migration of sand dunes
- polished appearance of rock surfaces
- marine fossils found in mountains
- bones of animals found on the ground

Could you tell me which one is correct?

marine fossils found in mountains