How does the rock cycle relate to the principal uniformitarianism?

Uniformitarianism is the idea that essentially the same geologic processes that are operating today have been the same for most (if not all) of Earth's history. Therefore, geologist believe that how they observer the rocks cycle today is how it has always been happening. This means that we can extrapolate the things we see happening today into the past to understand how rocks change from igneous to sedimentary to metamorphic.