Question

A geologist is studying an ancient stack of rock layers. Most of the layers contain fossils of shallow marine creatures (clams, corals,

etc.), suggesting the layers formed in a shallow ocean environment. But at the top of the stack, there is a layer that could only have
been deposited by a river.
What does this change in rock layers tell the geologist about Earth's history in the area where these layers formed? (Assume the
layers have not changed position since they formed.)

Answer 1

Answer: The environment changed suddenly from a shallow ocean setting to a river system.

Explanation: Changes seen in rock layers represent changes in Earth's local history. The rock layer stack overall shows a shallow ocean setting. But the youngest layer at the top was deposited by a river. This shows the geologist that the local environment changed suddenly from an ocean setting to a river system.