Dinosaur-Killing Firestorm Theory Questioned

New researchchallenges the idea that the asteroid impact that killed the dinosaurs alsosparked a global firestorm.

Scientistsmodeled the effect that sand-sized droplets of liquefied rock from the impact hadon atmospheric temperature. The asteroid is thought to have gouged out the Chicxulub crater on the Yucat?n Peninsula inMexico.

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

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

A new theory

But a newcomputer model, detailed in a recent issue of the journal Geology, suggeststhat the first barrage of falling spherules coalesced into a descending opaquecloud about 40 miles (70 km) above the Earth?s surface, shielding our planet(and the dinosaurs) from the heat of spherules rainingdown from above.

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

"Sopreviously entered spherules help to shield the ground of some fraction of thethermal radiation from the subsequently entering spherules."

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

The Earth'satmosphere likely did heat up, Goldin said, but the temperature increase maynot have been as dramatic or as long-lasting as previously estimated.

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

Burning oil

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

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

She added thateven if the Chicxulub impact didn?t cause trees to catch fire worldwide, italmost certainly triggered other environmental catastrophes that contributed tothe dinosaurs? demise, such as global dimming and acid rain.

?Just becausewe didn't have a global firestorm doesn't mean that Chicxulub is not the causeof the [dinosaurs?] extinction,? she said.

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