Dinosaur-killing space rock 'was a comet'

The impact 65 million years ago killed off 70% of
species on Earth - including the dinosaurs

The space rock that hit Earth 65m years ago and is widely implicated in the end of the dinosaurs was probably a speeding comet, US scientists say.

Researchers in New Hampshire suggest the 180km-wide Chicxulub crater in Mexico was carved out by a smaller object than previously thought.

Many scientists consider a large and relatively slow moving asteroid to have been the likely culprit.

Details were outlined at the 44th Lunar and Planetary Science Conference.

But other researchers were more cautious about the results.