Around the world, erosion draws sand off of beaches and into the sea. So engineers periodically dredge the sand from offshore and pump it right back onto the beaches. This has been going on for decades. (And occasionally they dredge up bombs!)

Part of our sand-loss problem is that billions of tons of sand are also used in construction (most notably in concrete), effectively locking it up so it can't be reused on beaches. So, over the long haul, we are running out of sea sand.

Why not just use desert sand for the construction stuff? We have lots of deserts in the world, with lots of relatively bomb-free sand in them! Sadly, desert sand doesn't work for construction because of its chemical composition. So for now we're stuck using a resource that is only renewable on an extremely long timeline, as waves crash onto shores.

Check out this video from Tom Scott to learn more about the problem—and learn about illegal sand mining too!