Science: Asteroid that killed dinosaurs will strike again - in 35 million years

The asteroid impact that wiped out the dinosaurs 65 million years ago was caused by a comparatively small meteor of the size which could be expected to hit the Earth once every hundred million years, according to British scientists.

Mike Warner, of Imperial College, London, working with a team from the US, Mexico and Canada, has determined that the "Chicxulub impact" - near the Gulf of Mexico - was caused by an asteroid about 100km (60 miles) across. This puts it "at the low end of the estimates", said Dr Warner. "The range did go from about 80km across to 200km." The results are published today in the science journal Nature.

But that also means that humanity is at greater threat from such random events, since the probability of impacts falls as the size of the body increases. "In evolutionary terms, 100 million years is pretty often," he said. "Whereas something 200 km across would only hit us about once every billion years. There will be another impact which will have dramatic consequences; and it will happen sooner than we had imagined."

Scientists are increasingly concerned that we have no co-ordinated means of detecting asteroids which could hit the Earth, and that even if we did there would be no agreed method of diverting them. A recent survey by Nasa suggested that there are thousands of "near-Earth" objects ranging from a few hundred metres to some kilometres in size still wandering within our orbit around the Sun. Yet governments have proved reluctant to provide funding for dedicated observatories.

Dr Warner commented, "We're used to thinking that mammals and humans appeared because they were better than what we replaced. But this event shows that the dinosaurs and the reptiles were just unlucky ... If it hadn't happened, they would still be here. Evolution is a more random process than we think."