A single, gigantic asteroid slammed into Earth 65 million years ago, dooming the dinosaurs and many other species, scientists said on Thursday in a new study rebutting theories that multiple impacts did the deed.

An examination of rock sediments drilled from five sites at the bottom of the Atlantic Ocean strongly supports the notion that one massive hunk of space rock caused the mass extinction, a research team led by University of Missouri-Columbia geology professor Ken MacLeod found.

"It's a completely straightforward, single-impact scenario," MacLeod, whose findings appear in the Geological Society of America Bulletin, said in an interview."It was a haymaker that nobody saw coming. One shot, and that's all you need to explain it."