Do you see how the ground level is higher on the left-hand side of this photo? To the right of the stone wall, the ground distinctly drops by a foot or more.
That wall is more than 200 years old. It marks the border between what was once a plowed field (on the left) and grazing pasture (on the right). Today, this site is woodland—part of the Harvard Forest, the most-studied forest in the world. But for generations, this land was farmed by Jonathan Sanderson and his descendants. And, even two centuries later, you can still see the way different uses of the land changed the land.
For instance, the ground level is higher on the left because plowed fields erode more easily. This site is on a slight slope. Water runs downhill, toward the right hand corner of the photo. As it did that, it carried bits of plowed field along with it—sediment that washed up against the stone wall and stayed there. Over many years, the effect changed the level of the land.
This isn't necessarily a catastrophic thing. But it is change. I spent last weekend in the Harvard Forest, participating in science in a hands-on way as part of the Marine Biological Laboratory's science journalism fellowship. One of the things I learned during my stint in the forest: The past ain't past. History is recorded in geology and ecology as surely as it's recorded in books. Very cool stuff!