(CNN)-- Tiny diamonds found in the soil are "strong evidence" a comet exploded on or above North ... in a cooling period known as the Younger Dryas. "A rare swarm" of comets rained over North ...

and quartz at depths showing they would have been exposed in the Younger Dryas period. The researchers believes it all adds up to a comet—or, at least, the remains of one—hitting Earth.