Dinosaur-Killing Firestorm Theory Questioned (SPACE.com)

New research
challenges the idea that the asteroid impact that killed the dinosaurs also
sparked a global firestorm.





Scientists
modeled the effect that sand-sized droplets of liquefied rock from the impact had
on atmospheric temperature. The asteroid is thought to have gouged out the Chicxulub crater on the Yucatán Peninsula in
Mexico.





It was
previously thought that the falling spherules, as the tiny rocks are called,
heated up the atmosphere by several degrees for up to 20 minutes — hot enough
and long enough to cause whole forests to spontaneously burst into flames.





As evidence for
this, scientists pointed to what appears to be carbon-rich soot from burned
trees discovered in the thin band of debris dating back to the impact some 65
million years ago, a shift in geologic time called the K-T boundary.





A new theory





But a new
computer model, detailed in a recent issue of the journal Geology, suggests
that the first barrage of falling spherules coalesced into a descending opaque
cloud about 40 miles (70 km) above the Earth's surface, shielding our planet
(and the dinosaurs) from the heat of spherules raining
down from above.





"As more
and more spherules are injected into the upper atmosphere, the cloud of
settling spherules becomes thicker and denser," study team member Tamara
Goldin of the University of Vienna told SPACE.com.





"So
previously entered spherules help to shield the ground of some fraction of the
thermal radiation from the subsequently entering spherules."





This
"self-shielding" may have prevented global wildfires and limited
other environmental effects from the impact, Goldin said.





The Earth's
atmosphere likely did heat up, Goldin said, but the temperature increase may
not have been as dramatic or as long-lasting as previously estimated.





"If you were on
the ground, it would feel at the maximum like you're under a broiler in your
oven," she said. "It would not be very comfortable, but it would not
be instant immolation."





Burning oil





So if burning
forests didn't create the K-T boundary soot, what did?





Some scientists
have suggested the soot might have been caused by the burning of petroleum in
the rocks of the Chicxulub impact site when the asteroid struck. "We know it's a pretty
oil-rich area today," Goldin said.





She added that
even if the Chicxulub impact didn't cause trees to catch fire worldwide, it
almost certainly triggered other environmental catastrophes that contributed to
the dinosaurs' demise, such as global dimming and acid rain.





"Just because
we didn't have a global firestorm doesn't mean that Chicxulub is not the cause
of the [dinosaurs'] extinction," she said.




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Original Story: Dinosaur-Killing Firestorm Theory Questioned
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