Scientists find dinosaur fossils in bottom rock layers of a cliff and mammal fossils in the middle rock layer of the cliff. Which could best be concluded from this evidence?

• A. Dinosaurs ate plants.
• B. Dinosaurs were eaten by the mammals.
• C. Dinosaurs lived on Earth before the mammals.
• D. Dinosaurs and mammals lived at the same time.

Answer: (C)

The main idea is that rock layers preserve a timeline: deeper layers are older, and newer layers sit on top of them. This is the principle of relative dating. Fossils in lower layers formed earlier than fossils in higher layers.

Here, dinosaur fossils are in the bottom layer, and mammal fossils are in the middle layer above. That order means dinosaurs existed earlier than the mammals. So the best conclusion from the evidence is that dinosaurs lived on Earth before mammals.

This interpretation doesn’t support statements about what dinosaurs ate or whether dinosaurs and mammals lived at the same time. It only tells you the sequence in which these groups appeared in the rock record at this site.