[meteorite-list] Day From Hell May Have Killed Off Dinosaurs

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Oct 27 13:06:13 2004
Message-ID: <200410271657.JAA21550_at_zagami.jpl.nasa.gov>

http://www.reuters.co.uk/newsPackageArticle.jhtml?type=topNews&storyID=610337

Day from hell may have killed off dinosaurs
By Alistair Bell
Reuters
October 27, 2004

YAXCOPOIL, Mexico - 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 (100-metre) tsunamis when the asteroid impacted
near today's Gulf of Mexico shoreline at a speed of 33,750 mph (54,000 kph).

Then, a column of red-hot steam and dust soared thousands of miles (km)
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 (160 km) in radius is now buried 1/2 mile
(1 km) 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.
Received on Wed 27 Oct 2004 12:57:01 PM PDT