If you look around during any random moment in your day, there’s a good chance that you’ll see a busy, fast-moving human world laid on top of a placid, mostly still natural world. The cars rush by loudly; the Earth sits passively, negligibly responsive to whatever befalls it. 

But this belies the range and magnitude of what is happening around us. From the seemingly vacuous space above our atmosphere to the very deepest part of the planet, almost every part of our environment is in constant motion. Some of it churns at literally glacial speeds; some of it whooshes by at almost the speed of light. Altogether, this constant activity is essential to the type of world we live in. If the natural world were as idle as it sometimes appears, there would certainly be no humans around to observe it.