Question

Which statement about how geologists study the ages of rock layers is true?

The law of superposition means that older rocks are on top.
Geologists can find the exact age of a rock by looking at its relative position.
The principle of original horizontality provides the basis for the law of superposition.
Relative age can be determined by using the concept of unconformity.

Answer 1

The statement that is true is:

**The principle of original horizontality provides the basis for the law of superposition.**

This principle states that sedimentary rocks are originally deposited in horizontal layers. When these layers are tilted or folded, the law of superposition can be applied, which states that in an undeformed sequence of sedimentary rocks, the oldest layers are at the bottom and the youngest are at the top.

To clarify the other statements:
- The law of superposition means that older rocks are on the bottom, not on top.
- Geologists often use relative dating techniques rather than precise absolute ages by examining rock position.
- While unconformities can help in understanding relative ages, they do not serve as a primary method for determining relative age by themselves.