The diagram above shows a stack of rock layers. Examine the diagram, and answer the question that follows. Layer T contains a well-known index fossil that is 120 million years old. Layer R contains a different index fossil that is 100 million years old. Based on this information and the principle of superposition, how old is Layer M?

Question

The diagram above shows a stack of rock layers. Examine the diagram, and answer the question that follows. Layer T contains a well-known index fossil that is 120 million years old. Layer R contains a different index fossil that is 100 million years old. Based on this information and the principle of superposition, how old is Layer M?

younger than 100 million years
either 20 million years or 220 million years.
older than 120 million years
between 100 million and 120 million years old.

Answer 1

Based on the principle of superposition, Layer M would be younger than both Layer T and Layer R. Since Layer T is 120 million years old and Layer R is 100 million years old, Layer M must be younger than both, so the age of Layer M would be between 100 million and 120 million years old.