Answer: A. the shale must be older, according to the principle of superposition
Explanation:
The layers of the surface of the earth have been formed over a long period of time. Rock pieces, sand and mud from water bodies form sediments and over time the bottom layer becomes rocks. Dead organisms trapped in these materials become fossils and mud is transformed into shale.
Looking at any of these transformed layers of the earth crust, we can conclude on their age and which was formed earlier, thanks to the law of Superposition. This law states that any given layer must be younger than the layer below it. Because shale is formed under sandstone, the shale is older.
