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Cretaceous Extinction - No "Nuclear Winter"?



http://dsc.discovery.com/news/briefs/20041108/honeybee.html

Bees Challenge Dino-Killer Winter Theory

Nov. 10, 2004  Tropical honeybees and other warmth-loving insects are
continuing to challenge the idea that a "nuclear winter" enshrouded the
Earth for years after the asteroid impact that killed the dinosaurs 65
million years ago.

The survival of the tropical honeybee Cretotrigona prisca beyond the
gigantic end-Cretaceous extinction is a sure sign that it could not have
been cold for long, said University of New Orleans graduate student
Jacqueline M. Kozisek.
...
 "These tropical honeybees were very, very close to modern tropical
honeybees," said Kozisek.

So close that those preserved in amber might have had similar limits to
how much cold they could stand. They might also have been the ancestors of
today's tropical honeybees, she said.

Today's tropical honeybees thrive at 88 to 93 degrees Fahrenheit
(31-34Celsius), according to entomological researchers, Kozisek said. The
same goes for the flowering plants off which they make their living.

If modern tropical honeybees are any measure, any post-impact cooling from
debris blocking sunlight could not have lowered temperatures more than 4
to 13 degrees (2-7C) without rubbing out bees. Current nuclear winter
theories from the Chicxulub impact estimate drops of 13 to 22 degrees F
(7-12C), too cold for tropical honeybees.

"We know that countless other lineages of tropical plants, insects, fish
and reptiles also survived," said paleontologist Peter Wilf of
Pennsylvania State University. "The asteroid didn't kill everything
everywhere, or we wouldn't be here today."

In recent years, paleontologists have been gathering increasing evidence
that the event that killed off 70 percent of species 65 million years ago
was very selective, Wilf said.

One recent study calls on a massive heat pulse caused by debris reentering
the atmosphere after being shot into space by the impact at Chicxulub, he
said. Such a blast of heat would have only lasted a few hours and killed
only organisms unable to hide in water or other shelter.

For that reason, the news of tropical honeybees surviving comes as no
surprise, Wilf said.

Kozisek conducted her study by searching the paleontology literature for
information about organisms that appears to have survived the extinction
event. She then picked out tropical honeybees because they had almost
indistinguishable modern relatives and a narrow temperature range.