Rivers on Earth carve winding paths through landscapes, shaping the terrain over time. At first glance, their meandering ...

They’re studying the river by taking photos of all the different things they can spot. Can you see that tree that's got like that? Children: Looks a bit like an arch. De-Graft: Yeah, like an arch!

And after it’s gone over its last rapids and tumbled over its last fall, it becomes a very different river indeed. As the river gets older, it slows down. A minor obstacle in its path is now ...