Before wind and water can carry material away, rock first has to break down. Geologists call this process "weathering." As the name suggests, weathering is controlled by things like wind and rain, and it comes in two basic forms. Chemical weathering happens when substances like water or acids get into rock and react with the minerals that make up the rock. You may have noticed that if you leave your bike or other steel object out in the rain, it tends to get rusty. Well, it turns out that the same thing happens to certain minerals inside rocks. After enough time, these minerals change so much that they simply crumble.

Mechanical weathering happens when things like ice physically break rock apart. If you have ever left a can of soda in a freezer too long, you know that when water freezes to ice, it expands so much that it may actually split the can apart. The same thing happens when rain gets inside rocks and freezes. Known as "frost wedging," this process can reduce solid rock to tiny pieces in just a few short years!

Once weathering breaks a rock down, then it's up to gravity to move them along. That's right, I said GRAVITY! Think about it. Why does water flow downhill? Gravity! What makes a rockslide happen? Gravity! Why do your pants fall down when they're too big? Gravity! It turns out that if it wasn't for gravity always pulling things down, very little erosion would actually happen! Now that we've got you thinking about how erosion works, it's time to observe and record!