Answer :
Final answer:
The Law of Superposition is used to determine the relative ages of rocks, stating that the oldest rocks are at the bottom of an undisturbed sequence of sedimentary rocks.
Explanation:
The geologic principle used when a geologist observes an outcrop of rocks and determines that the bottom layer is the oldest is the Law of Superposition. This principle states that in an undisturbed sequence of sedimentary rocks, the oldest rocks are found at the bottom while the youngest are at the top.
Furthermore, the principle of original horizontality emphasizes that sediments accumulate in essentially horizontal layers. If tilted sedimentary layers are observed today, it indicates they have been subjected to tectonic forces.
For example, in Figure 5, if rock layer A is at the bottom, followed by layer B and then layer C, applying the Law of Superposition helps determine their relative ages.
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