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TheEveningStar
28-10-04, 17:06
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By Alistair Bell

YAXCOPOIL, Mexico (Reuters) - One minute you're a big T-Rex, the next you're toast.

Challenging conventional theory, new scientific research suggests the dinosaurs may have been scorched into extinction by an asteroid collision 65 million years ago that unleashed 10 billion times more power than the Hiroshima nuclear bomb.

Earth's temperatures soared, the sky turned red and trees all over the planet burst into flames, said atmospheric physicist Brian Toon of the University of Colorado.

Among the few survivors would have been animals living in water or burrowed in the ground like turtles, small mammals and crocodiles.

"Essentially, if you were exposed you were broiled alive. That is probably what happened to the dinosaurs. They were big creatures that didn't have anywhere to hide," said Toon.

Scholarly debate over how the dinosaurs died is fierce and the theory put forward by Toon and others adds one more twist to the greatest forensic mystery of all time.

Despite opposition from some scientists, the idea that the dinosaurs were killed by an asteroid that slammed into Mexico's Yucatan peninsula has won general acceptance since it was first mooted in the early 1990s.

Under that argument, academics say the giant reptiles mostly froze or starved to death when a huge cloud of particles kicked up by the meteorite blocked the world's sunlight for months.

But Toon, the co-author of a study published in the Geological Society of America Bulletin in May, reckons the dinosaurs' end was even more dramatic.

Creatures living near ground zero would have been vaporized immediately while those in the Caribbean area and southern United States would have drowned in 330-feet-high tsunamis when the asteroid impacted near today's Gulf of Mexico shoreline at a speed of 33,750 mph.

Then, a column of red-hot steam and dust soared thousands of miles into space and most of it fell back toward Earth within a few hours, turning the heavens into hell.

GIANT FIRE

"The entire sky would be radiating at you. It would be like standing next to a giant fire; you'd be burned very severely," Toon said, whose research is based on mathematical and computer models.

Land dinosaurs all around the world perished from the intense heat of several hundred degrees Fahrenheit, said Toon.

He agrees with other scientists that the dust cloud later cooled and blocked out the sun, but says the land dinosaurs were already history by that time.

The darkness finished off many of the remaining marine reptiles and fish by killing plankton and disrupting the food chain, said Toon.

But those views are being challenged by some researchers who say the Yucatan meteorite was not as great a catastrophe as first thought.

A theory gaining ground is that global warming combined with another asteroid collision in an unknown location other than the Yucatan was what cut short the dinosaurs' reign.

The academics are unlikely to agree soon on what caused the demise of the Triceratops, Sauropods and their kin but in the jungly Yucatan peninsula, locals are in no doubt.

"Everyone knows that the asteroid here killed the dinosaurs. They teach it in the schools," said Isabel Lopez, a shop owner in the village of Yaxcopoil.

"It's a shame what happened," said schoolboy Daniel Tzeu, 11, lamenting the dinosaurs' end. He was standing near a bore hole in the village dug by University of Arizona scientists probing for rock samples in a crater caused by the asteroid.

The crater, around 100 miles in radius is now buried 1/2 mile underground, partly beneath the sea.

The University of Arizona has found "shocked" rocks it says could only have been damaged by an asteroid collision.

David Kring, one of the University of Arizona scientists who proved the Yucatan crater was the asteroid crash site, agrees the catastrophe killed off the land dinosaurs but doubts they all burned to death.

Many starved when plants were destroyed by fires, a subsequent period of global darkness and acid rain.

"If you knock out the vegetation you really have undermined the food chain," he said.

WRONG ASTEROID?

But Princeton University geologist Gerta Keller disagrees that the asteroid put paid to the dinosaurs. She says asteroid debris, known as ejecta, found embedded in ancient rocks shows the Yucatan meteorite hit Earth many millennial before the dinosaurs vanished.

"The ejecta everywhere is in sediment layers that pre-date the mass extinction by about 300,000 years," she said.

Global warming caused by 400,000 years of repeated volcanic eruptions in western India weakened the dinosaurs and then another asteroid struck earth, although scientists have yet to find its crater, Keller said.

"It's a double whammy at that point," she said.

A combination of the two disasters deprived the Earth of oxygen and the dinosaurs probably suffocated to death, she said.
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