 And one of Charles Darwin's mentors coined the term uniformitarianism. In other words, the processes that happen today were happening in the past. And the processes we're talking about here with these students is basically fluid flow and movement of particles in that fluid. We know that when there was lots and lots of fluid, in other words, a big river moving really fast, you can move big rocks. And if it's not moving that fast, you can only move smaller rocks and smaller rocks and smaller rocks until, if it's not moving at all, it won't move. A lot of what we study is we work out what it was like in the environment as you go back in time. Or actually sediments, in other words, rocks that have moved around that have been deposited on the surface of the planet. And they can tell us about what the environment was like at that time. And that's key. So when we go to places where you can see the rocks exposed in the field, like down at the beach on those sea cliffs or when you're driving down a highway and you see the cuts in the rocks, people like me can read stories from those rocks and know what that environment was like.