The oldest rock layer in an undisturbed rock sequence occurs

The correct answer is at the bottom.

Explanation:

The principle of superposition illustrates that in the arrangement of layers, any layer is considered younger, which is present above the layer on which it rests, thus, the below present layer is considered older than the one, which rests upon it. This is known as the law of superposition and is one of the general principles of geology.  

According to the principle of superposition, in an undisturbed sequence of rocks, each layer of rock is older in comparison to the one, which is present above it and is younger in comparison to the one present below it. Thus, it can be concluded that the youngest rocks are present at the top, while the oldest rocks are found at the bottom.  

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