Use the geological cross-section to determine the age of rock layer D as precisely as possible.
A)It is 40 million years old.
B)It is between 39 million years old and 25 million years old.
C)It is between 39 million years old and 17 million years old.
D)It is older than 17 million years old.

Question

Use the geological cross-section to determine the age of rock layer D as precisely as possible.
A)It is 40 million years old. 
B)It is between 39 million years old and 25 million years old. 
C)It is between 39 million years old and 17 million years old. 
D)It is older than 17 million years old.

Quizplus · Accepted Answer

Taking a look at the cross-section, we can see that rock layer D is composed of sedimentary rock that lies on top of a layer of igneous rock that is dated at 39 million years old. Therefore, we know that rock layer D must be younger than 39 million years old. We can also see that rock layer D is cut through by a fault that is dated at 17 million years old. Therefore, we know that rock layer D must be older than 17 million years old. Based on this information, the best choice is C: It is between 39 million years old and 17 million years old.

Use the Geological Cross-Section to Determine the Age of Rock