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Monday, 18 December, 2000, 16:29 GMT
Researchers to drill into dinosaur crater
Rock Nature
A fragment of the space rock (left) that smashed into Earth
Scientists are to drill into the giant crater zone on the Earth's surface that many believe is linked to the disappearance of the dinosaurs 65 million years ago.

The researchers want to understand the precise mechanics of how an environmental disaster could have resulted from the asteroid or comet strike that produced the 200-kilometre (125-mile) wide Chicxulub crater on Mexico's Yucatan Peninsula.

Most agree that the impact would have thrown vast amounts of dust and debris into the atmosphere which would have blocked out sunlight and restricted plant growth, the vital first link in all ecosystems.

But recent computer and field studies have suggested the collision may not have been powerful enough to throw sufficient debris skyward to shroud the planet for long enough to produce the mass extinction seen in the fossil record.

Scientists presented findings at the autumn meeting of the American Geophysical Union, in San Francisco, which indicated that dust from the impact reacted with the Earth's atmosphere to create a deadly sulphuric acid and carbon dioxide mist.

High impact

"It had to be some kind of atmospheric chemistry," concluded Professor Buck Sharpton of the Department of Geology and Geophysics, University of Alaska Fairbanks, US. "That's the only way the impact would have had a global reach."

In June, scientists will drill 2.4 kilometres (1.5 miles) into the crater to gain a better insight into the force of the collision, and its environmental results. The drilling site is about 80 kilometres (50 miles) south of Merida, Mexico.

About 60% of all recorded species on the Earth disappeared around the time the huge space object hit.

Professor Sharpton and his team hope core samples will give researchers a better understanding of the some of the atmospheric interactions that took place when all the dust and debris was thrown many kilometres into the air.

Specifically, the team want to know more about the role played by sulphur and carbon-bearing rock. "This is going to tell us a lot about how these carbonates and sulphates react to high impact pressures," Professor Sharpton said.

Competing theory

Gypsum rock evaporated by the impact might have clogged the atmosphere with floating sulphur particles, causing a "nuclear winter" by blocking sunlight and removing the essential first link in the worldwide food chain.

Sulphur particles falling into the ocean could also have transformed the world's seas into vast, acidic pools, killing off much of the sea life.

"You can't initiate an extinction event unless you wipe out all the critters," Professor Sharpton said, noting that the environmental effects of the impact would have to have been felt worldwide in order to account for the planetary extinction of so many species.

The main competing theory to explain the disappearance of the dinosaurs centres on the upsurge in volcanic activity on the Earth that occurred at the same time as the space impact.

A huge flood of lava covered much of present-day India. Sulphur dioxide unleashed by this supervolcanism would have created hellish acid rain, while an increase in carbon dioxide would have caused dramatic greenhouse warming.

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18 Sep 00 | Sci/Tech
Call for asteroid defences
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