They claim they have found a 200-mile-wide undersea crater off the coast of the Falklands created as the huge lump of space rock fell to Earth at a closing speed of some 600,000mph.
Such was the devastation that about 95 per cent of animal species were wiped out. Giant reptiles became extinct, to be replaced eventually by the dinosaurs.
The scenario was greeted with incredulity by scientists attending last week's meeting of the American Geophysical Union in San Francisco, where the case for it was argued by two independent groups of researchers - led by Michael Rampino, professor of earth sciences at New York University, and Verne Oberbeck, a scientist at Nasa's Ames Research Centre in California.
A giant supercontinent covering the Earth at the time eventually split into the northern Laurasia and southern Gondwanaland. Professor Rampino and the Nasa scientists believe fractures caused by the asteroid as it hit the southern tip of what became Gondwanaland determined the future shape of the southern continents.
Shock waves from the impact spread out from the crater causing the triangular shapes of present- day South America, southern Africa, India and western Antarctica, Professor Rampino said. 'If this is what controlled the zones of breaking of the continents, then without the asteriod impact the continents may have broken up along different lines and the Earth would look very different today.'
Continental drift - the theory that the continents are constantly moving as the Earth's 'tectonic plates' slide apart - is the accepted theory of how today's land masses were formed.
The most controversial aspect of the theory is that the asteroid impact caused the mass extinction of animals about 250 million years ago. But Tony Hallam, professor of geology at Birmingham University, is sceptical. 'It's a very spectacular idea, but unless you can date it accurately, it remains wild speculation.'
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