- Most dinosaurs were incinerated in a matter of hours
after an asteroid impact 65 million years ago kicked up a global rain of
broiling debris, according to a new study.
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- Anything not underground or protected by water was wiped
out.
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- The research builds on previous studies that concluded
the die-off was rapid. The new analysis presents a plausible scenario of
swift death, outside experts said, but they caution that the fossil record
for an event so long ago cannot discern whether the extinction played out
over hours or years.
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- For more than a decade, most researchers have been convinced
that an asteroid was responsible for the death of the dinosaurs. Recently
however, a handful have argued that a combination of effects -- an asteroid
along with perhaps increased volcanic activity and climate change, or even
a second asteroid -- caused a slow demise of the giant animals.
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- The new study reviewed existing geologic evidence for
the known impact and considered interesting patterns in species survival.
How did some birds, mammals, crocodiles, snakes and other animals endure
the calamity that wiped out larger species?
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- Take cover
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- The survivors burrowed underground or were protected
from the firestorm by swamps or oceans, says study leader Doug Robertson
of the University of Colorado at Boulder. The details were published in
the May-June issue of the Bulletin of the Geological Society of America.
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- There's no question over whether an asteroid hit. The
roughly 6-mile-wide (10-kilometer) space rock carved out the Chicxulub
crater off Mexico's Yucatan Penninsula. Previous work uncovered a global
layer of material that had melted and then hardened when the impact vaporized
terrestrial rock. Robertson and his colleagues argue that superheated stuff
was blasted from the crater into a suborbital path around Earth, generating
a "heat pulse" upon re-entry.
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- "The kinetic energy of the ejected matter would
have dissipated as heat in the upper atmosphere during re-entry, enough
heat to make the normally blue sky turn red-hot for hours," Robertson
said.
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- All unprotected creatures were "baked by the equivalent
of a global oven set on broil."
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- Jay Melosh, a University of Arizona scientist who was
not involved in the new study, is one of several researchers who have presented
similar asteroid-impact scenarios in the past. Melosh said Robertson did
some "heavy lifting" on the idea by fleshing it out along with
paleontologists.
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- "I think this is the most likely scenario for the
death of the land fauna," Melosh told SPACE.com. He added, however,
that the idea does not explain ocean extinctions, "which were pretty
extensive also."
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- Hard to prove
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- Paleontologist David Fastovsky of the University of Rhode
Island agrees that dinosaur extinction appears to have been rapid. It did
not take thousands of years, he said in a telephone interview. Fastovsky
presented a similar heat-killing scenario more than a decade ago with Brown
University researcher Peter Schultz.
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- Fastovsky said Robertson's team took a useful and unique
look at the situation by combining geophysical and paleontological evidence.
But he notes that trying to glean precise timing from fossils is like trying
to remember what you were doing at a certain moment years ago. The die-off
may have taken just hours, he said, but that's not discernable from the
fossil record.
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- "By itself, the fossil record can't distinguish
between a minute and a hundred years for something that happened 65 million
years ago," Fastovsky said.
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- That leaves the open the question of exactly how the
agony played out, but few doubt the general scenario now.
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- "Dinosaurs and many other species simply stop to
exist," said Benny Peiser, a researcher at Liverpool John Moores University
who monitors research on catastrophes and mass extinctions. "Those
lucky few that may have survived the hellish impact fires, heat pulse,
radiation, and so on would have struggled to cope with a dramatically deteriorating
environment, including the probable 'impact winter' that most likely destroyed
the food chain."
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- Copyright © 2004
- SPACE.com.
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