Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Example input: Earth rotates on its axis once times in one day.
Example output: How many times does Earth rotate on its axis in one day?
Example explanation: The given output correctly poses a question based on the scientific fact given.
Q: Deeper layers of rock must be older than layers closer to the surface, this is the law of superposition.
A:
Deeper layers of rock must be older than layers closer to the surface, this is the law of what?