Question

you can tell that the oldest rocks are at the bottom of an undisturbed rock sequence by using the principle of
suerposition.
uniformitarianism.
cross - cutting relationships.
original horizontality.

Explanation:

The principle of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest rocks are at the bottom and the youngest are at the top. Uniformitarianism is the idea that the same geological processes that operate today have operated throughout Earth's history. Cross - cutting relationships are used to determine the relative ages of rocks where one rock body cuts through another. Original horizontality states that sedimentary layers are originally deposited horizontally.

Answer:

superposition.