Question

1. If you find a rock in the hills that contains a trilobite fossil, what might that fossil tell you about the hills?
2. Why do geologists believe that volcanic activity was more common in the past than it is today?

Answer 1

This is an answer for number one ONLY. 
Trilobite are prehistoric marine arthropods. They were sort of like crabs or spiders. The fossil was found on a hill. Hills are on land, and the trilobite lived in water. Unless left there by a previous visitor, the fossil tell that the hills were once underwater.