prize9-1, Exercise 1: The present is the key to the past

Model answer (check the details):

Hutton argued that the slow processes we can watch today, such as rivers carrying sediment or lava cooling, also made the rocks we find. It is a fact about rocks, because the evidence shows they formed by such processes, and a method, because it tells you how to test an explanation: ask whether a process we can observe could produce what the rock shows.

Example: ripple marks in an ancient sandstone look like the ripples in a modern river bed or beach, so the sandstone was probably laid down by moving water.

Care: the principle does not say that rates never changed. Some events, such as large impacts, were sudden.