Richard Norris, who has been leading the international sea-drilling expedition which made the find, said the discoveries were "proof positive. We've got the smoking gun".
The evidence appears to substantiate the theories of geologists such as the Californian Walter Alvarez, who has championed the theory that dinosaurs disappeared from fossil history because of such an impact.
Robert Corell, of the National Science Foundation in the United States, said the samples were the strongest evidence yet that an asteroid impact caused the extinction. "In my view this is the most significant discovery in geosciences in 20 years," he said.
The expedition has recovered three drill samples that have the signature of an asteroid impact. The samples include a thin brownish section that the scientists call the "fireball layer" because it is thought to contain bits of the asteroid itself.
Mr Norris said: "These neat layers of sediment bracketing the impact have never been found in the sea before."
Under the asteroid theory, the huge submerged crater at the Yucatan Peninsula, Mexico, was the impact point.
The scientists believed the violence of the impact would have been unlikely to leave clear samples. However, the resulting waves would have washed across Florida and deposited debris in the Atlantic - which was what they found when they drilled 300 feet beneath the sea-bed.
Mr Norris said the deepest - oldest - layers contained fossil remains of many animals which were living in a "happy-go-lucky ocean" just before the impact. Just above this was a layer with material from the bottom of the sea which was believed to have melted in the giant energy release of the impact.
Next was a rusty brown layer which the scientists believe to be the vapourised remains of the asteroid itself. And above all these were two inches of grey clay with barely anything in it which the team believes shows the asteroid wiped life out.
"It was not a completely dead ocean, but most of the species that are seen before (early in the core samples) are gone. There are just some very minute fossils. These were the survivors in the ocean," Mr Norris said. The dead zone lasted about 5,000 years and then there was evidence of renewed life.
The asteroid which landed on the Yucatan Peninsula would have been 6 to 12 miles in diameter and smashed to Earth at thousands of miles an hour to gouge the crater 150 to 180 miles wide. Up to 70 per cent of all species, including the dinosaurs, perished. Among the survivors, scientists believe, were small mammals that over millions of years evolved into new species including humans.
David Norman, director of the Sedgwick Museum in Cambridge, said the new finds simply added to the significant geophysical evidence which already existed to support the idea of an asteroid strike. But he said there was a problem with timing. Previous evidence from sediment suggested that the dinosaurs did not become extinct at exactly the same time as an impact occurred.Reuse content