Dinosaur-killing impact set Earth to broil, not burn

[n2doc]

07 December 2009 by Jeff Hecht

The asteroid impact that ended the age of dinosaurs 65 million years ago didn't incinerate life on our planet's surface – it just broiled it, a new study suggests. The work resolves nagging questions about a theory that the impact triggered deadly wildfires around the world, but it also raises new questions about just what led to the mass extinction at the end of the Cretaceous period.

The impact of a 10-kilometre asteroid is blamed for the extinction of the dinosaurs and most other species on the planet. Early computer models showed that more than half of the debris blasted into space by the impact would fall into the atmosphere within eight hours.

The models predicted the rain of shock-heated debris would radiate heat as intensely as an oven set to "broil" (260 °C) for at least 20 minutes, and perhaps a couple of hours. Intense heating for that long would heat wood to its ignition temperature, causing global wildfires.

Yet some species survived, and the global layer of impact debris doesn't contain as much soot as would be expected from burning the world's forests, raising questions about the extent of post-impact wildfires.

To explain the discrepancy, Tamara Goldin of the University of Vienna and Jay Melosh of Purdue University in Indiana studied how ejecta falling through the atmosphere might affect heat transfer from the top of the atmosphere to the ground. Earlier models considered only how atmospheric greenhouse gases would absorb heat.

The study reveals that the first debris to re-enter the atmosphere just a few minutes after the impact helped protect the surface from the debris that followed. "The actual ejecta themselves were getting in the way of the thermal radiation and shielding the Earth," Goldin told New Scientist.

more:

http://www.newscientist.com/article/dn18246-dinosaurkilling-impact-set-earth-to-broil-not-burn.html

[Vinnie From Indy]

1. Many scientists speculate that the extinction event had many deadly players

The ejecta certainly did major damage to life, but the impact had more death to dish out than that. The impact also released a gargantuan amount of material that slowly precipitated back to earth in the form of acid rain after the fires had ceased. This certainly had a major impact on phyto-plankton which led to a food chain disaster.

[groovedaddy]

2. Would a 10km astroid impact with sufficient shock to trigger plate activity, localized or greater?

I remember reading the novel "Lucifer's Hammer," which, while fiction, claimed to rely upon scientific evidence of what such an impact would be like. I think that one hit the ocean, generating 1,000 thousand feet high psunamis.

[kentauros]

3. I remember that book!

That was the Gulf of Mexico impact, with surfers riding the waves well past Houston, sixty miles inland! ;)

As I recall, there was one impact in the Atlantic, east of Florida and the waves swept over it before the one in the Gulf hit, sweeping back the other way, pretty much wiping the peninsula clean :o