Answer:
A. different time periods
Explanation:
The contents of the layers are from different time periods based on the law of superposition of strata.
This law states that "in an undisturbed sequence of strata, the oldest layer can be found at the bottom and the youngest on top".
The rock layers and their contents are usually from different time periods. Most times biostratigraphic study of the strata would reveal the ages of the beds.
