Libyan desert glass, 29 million years ago was probably formed when an asteroid or comet hit the surface of the earth like a huge atomic bomb, unleashing enough destructive force to not only liquefy the rocks, sand and dirt at ground zero, but to splash the molten, mixed material up into the wispy outer atmospheric regions. Perhaps some escaped Earth's gravity altogether; the rest plummeted back in a rain of fire and molten glass. The crater marking the original impact site has not been discovered - no doubt it is under millions of pounds of sand.