Plate tectonics and rock layers
Convection in the mantle moves the plates, and undisturbed sediment layers record time with the oldest at the bottom.
A worked example
Plates separating at 2.5 cm per year move 2.5 x 10 000 = 25 000 cm apart over 10 000 years, which is 250 metres.
The mistake people actually make
Superposition only holds where the layers have not been overturned or faulted. Convert centimetres to metres by dividing by 100, not by 1 000.