ROANOKE TIMES
Copyright (c) 1997, Roanoke Times
DATE: Monday, February 17, 1997 TAG: 9702170104
SECTION: NATIONAL/INTERNATIONAL PAGE: A-1 EDITION: METRO
DATELINE: WASHINGTON
SOURCE: PAUL RECER ASSOCIATED PRESS
Scientists who drilled core samples from the ocean bed said Sunday they have found proof that a huge asteroid smashed into the Earth 65 million years ago and probably killed off the dinosaurs.
``We've got the smoking gun,'' said Richard Norris, leader of an international expedition that probed the Atlantic Ocean floor in search of asteroid evidence.
Norris said the expedition recovered three drill samples that have the unmistakable signature of an asteroid impact about 65million years ago. The drill cores include a thin brownish section that the scientists called the ``fireball layer'' because it is thought to contain bits of the asteroid itself.
``These neat layers of sediment bracketing the impact have never been found in the sea before,'' Norris said. ``It is proof positive of the impact.''
The scientists spent five weeks off the east coast of Florida collecting cores from the ocean floor in about 8,500 feet of water. The team penetrated to 300 feet beneath the seabed, drilling past sediment laid down at the time of the dinosaur extinction.
Norris said the deepest layers contain fossil remains of many animals in a healthy, ``happy-go-lucky ocean'' just before the impact.
Just above this is a layer with small green glass pebbles, thought to be material on the ocean bottom instantly melted by the massive energy release of the impact.
Next was a rusty brown layer Norris said is thought to be from the ``vaporized remains of the asteroid itself.''
The heat of the impact would have been so intense, Norris said, that the stony asteroid would have instantly been reduced to vapor and thrown high into the sky, some of it perhaps reaching all the way to outer space. It then could have snowed down, like a fine powder, all over the globe. Norris said brown deposits, like that in the core sample, have been found elsewhere and they have a high content of iridium, a chemical found in asteroids.
Just above the brown layer is 2 inches of gray clay with strong evidence of a nearly dead world.
``It was not a completely dead ocean, but most of the species that are seen before [early in the core sample] are gone,'' Norris said. ``There are just some very minute fossils. These were the survivors in the ocean.''
This dead zone lasted about 5,000 years, said the scientist, and then the core samples showed evidence of renewed life.
``It is amazing how quickly the new species appeared,'' he said.
Although the dinosaur-killing impact occurred in the southern Gulf of Mexico, Norris went to the Atlantic Ocean, near the edge of the continental shelf. He said that the violence of the impact, followed by huge waves, roiled the Gulf of Mexico so much that it is unlikely clear core samples would be found there.
He theorized that waves from the impact would have washed completely across Florida, depositing debris in the Atlantic. And that's where he found it.
Robert Corell, assistant director for Geosciences of the National Science Foundation, said the core samples are 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. ``This gives us the facts of what happened to life back then. I would certainly call it the smoking gun.''
The ship bearing the core samples returned to port Friday and the NSF announced the findings Sunday, just hours before NBC was to air a movie about a fictional asteroid hitting the Earth and causing widespread destruction.
``The impact of the asteroid featured in tonight's NBC-TV show is peanuts compared to the real thing faced by the world 65 million years ago,'' Corell said.
Geologist Walter Alvarez of the University of California, Berkeley, first proposed in 1980 that the dinosaurs disappeared from fossil history suddenly because of a massive asteroid hit. At first, the theory had few supporters.
But in 1989, scientists found evidence of a huge impact crater north of Chicxulub, on Mexico's Yucatan Peninsula. Later studies found evidence of debris washed out of the Gulf of Mexico by waves that went as far inland as Arkansas.
It's now widely believed that an asteroid 6 to 12 miles in diameter smashed the Earth at thousands of miles an hour, gouging a crater 150 to 180 miles wide.
That energy release was more powerful than if all of the nuclear weapons ever made were set off at once, Norris said.
Billions of tons of soil, sulphur and rock vapor were lifted into the atmosphere, blotting out the sun. Temperatures around the globe plunged.
Up to 70 percent of all species, including the dinosaurs, died off. Among the survivors, scientists believe, were small mammals that, over millions of years, evolved into many new species, including human beings.
LENGTH: Medium: 90 linesby CNB