Sand is the most abundant material on Earth. And, other than water and air, sand is the natural resource we consume more than any other -- more, even, than oil.

The pyramids are made of sand. Our roads and driveways and sidewalks are made of sand. Concrete buildings and their concrete foundations are made of sand. From computer chips to computer screens, window panes to light bulbs, breast implants to the Hubble telescope, sand is basically the essential building block of civilization.

Humans are estimated to consume almost 50 billion tons of sand and gravel every year.

Oh, and, by the way: We're running out of it.