I was walking along the lake shore, not thinking about anything in particular. Just casually looking at the birds, watching the dragonflies that hunt the small ponds along the lake, listening to the gulls arguing, enjoying the way the sand shifted under my feet. Here’s an interesting thing about sand: it behaves more like a liquid when it’s dry, and more like a solid when it’s wet.

I was just walking in the sand by the lake, idly scanning the ground for interesting chunks of driftwood or colorful stones. And I saw this:

Somebody had lost a beach shoe. Nothing really out of the ordinary. And a dog had padded by. Also pretty common; lots of people take their dogs to the lake. At some point, a raccoon had wandered along the same bit of sand; the woods around the lake are a haven for raccoon. And now I was standing there. That layering of temporal events pleased me for some reason — four creatures had crossed that same little patch of sand, separated only by a period of time.

This sort of thing happens to me all the time. I see something, and neurons start firing in my brain. I saw that lost beach shoe and the dog’s paw print and the raccoon track, and thoughts start turning over in my mind. Because it wasn’t just us that had crossed that bit of sand. Dozens of creatures had walked, slithered, or hopped across that same spot. Thousands of dozens. Millions of thousands of dozens. I mean, some three hundred million years ago, this entire area was under water; it was the sandy bottom of a great inland sea — a sea that dried up, only to be replaced by another inland sea a couple hundred million years later. Then that sea dried up as well. Now there’s just sand.

Well, not just sand. There’s also a lake. Six thousand acres of water. Almost ten square miles. Not a natural lake, though. Technically, it’s a reservoir — a man-made lake; an intentional containment of the Des Moines River. The lake was created about 50 years ago to try to control the periodic flooding that plagued the city of Des Moines for over a century. The flooding also troubled the native people who’d settled at the confluence of the Des Moines and Raccoon Rivers seven thousand years earlier.

We know people lived here seven thousand years ago because we’ve found their bodies. A woman and a child, well-preserved skeletons sealed in a layer of sandy clay deposited by a sudden flood. It’s only relatively recently that humans developed the technology (and the audacity and arrogance) to dam up the river and create a lake. The dam and the lake hasn’t put an end to the flooding, but it’s certainly reduced the damage.

A lost beach shoe and a raccoon print in the sand, and my mind went caroming off of disappearing Paleozoic seas and banging into ancient human settlements and human high-handedness toward nature. But even while a chunk of my brain was knocking around notions of time and human presumption, I couldn’t help being drawn by how gracefully the water and wind have shaped the lake shore.

I found myself paying attention to how the moisture content of the sand shifted its color along with its consistency — how the farther I got from the water, the more pale the sand became. I started to notice how the granularity of the sand changed — how some was more coarse and some was incredibly fine. I paid more attention to how the wind revealed layers of different color in the sand, how driftwood bleached into various subtle shades.

There was something wonderful and beautiful about how dried leaves gathered gracefully in fluid self-organized, breeze-driven groups. There was something fascinating about how different waterlines arranged themselves; you could gauge the strength of various storms by the arrangements of the detritus and the driftwood and how far they’d been driven from the waterline by the wind and the waves.

None of this is stable. It’s changing all the time. The change is sometimes radical and quick and violent, but mostly it’s slow. I know I can return to this same spot in a couple of weeks and find that same driftwood log and those same weeds; I know I can return in six months and find that same log, though it will likely be surrounded by different detritus. There is continuity. Continuity, but not sameness.

There’s a good chance that the next time I return to the lake, that lost beach shoe will still be there. The dog’s paw print and the raccoon track probably won’t. The sand, though, it’ll still be there. Long after I’m dead and gone, long after that shoe disintegrates, long after the driftwood deteriorates into nothing, the sand will still be there.

There are people who collect sand as a hobby. They’re called arenophiles. The word comes from the Latin term for sand: harena. That’s also the root of the word arena. What does sand have to do with an arena? The Romans understood that the best and easiest way to soak up the blood spilled from their arena spectacles — the gladiator fights, the chariot races, the beast contests — was to lay down a layer of sand. Before there was a Coliseum, there was sand.

There’s always sand.