A new theory on the origins of desert glass

Libyan Desert Glass is opaque, greenish glass formed when the desert sands fused in some sort of extremely hot incident. (Alternately, Sandman Volume 2 Number 9 proposes that the glass is the remains of an ancient city.) What, exactly, created the heat that made the glass is a source of scientific debate, but a new paper suggests it might have been the result of a comet impact. Why a comet and not, say, an asteroid? Scientists studied a stone found in conjunction with the glass and discovered that it contained a mixture of elements that you'd be unlikely to get from an asteroid impact. Instead, the elements suggest an origin outside our solar system's asteroid belt.