Chicxulub Crater, Yucatán Peninsula, Mexico – Artist’s Impression Image: University of Colorado
Posted on 03/28/2013 9:02:58 AM PDT by Ernest_at_the_Beach
From the AGU:
Global fires after the asteroid impact probably caused the K-Pg extinction
Chicxulub Crater, Yucatán Peninsula, Mexico – Artist’s Impression Image: University of Colorado
About 66 million years ago a mountain-sized asteroid hit what is now the Yucatan in Mexico at exactly the time of the Cretaceous-Paleogene (K-Pg) mass extinction. Evidence for the asteroid impact comes from sediments in the K-Pg boundary layer, but the details of the event, including what precisely caused the mass extinction, are still being debated.
Some scientists have hypothesized that since the ejecta from the impact would have heated up dramatically as it reentered the Earth’s atmosphere, the resulting infrared radiation from the upper atmosphere would have ignited fires around the globe and killed everything except those animals and plants that were sheltered underground or underwater.
Other scientists have challenged the global fire hypothesis on the basis of several lines of evidence, including absence of charcoal-which would be a sign of widespread fires-in the K-Pg boundary sediments. They also suggested that the soot observed in the debris layer actually originated from the impact site itself, not from widespread fires caused by reentering ejecta.
Robertson et al. show that the apparent lack of charcoal in the K-Pg boundary layer resulted from changes in sedimentation rates: When the charcoal data are corrected for the known changes in sedimentation rates, they exhibit an excess of charcoal, not a deficiency. They also show that the mass of soot that could have been released from the impact site itself is far too small to account for the observed soot in the K-Pg layer. In addition, they argue that since the physical models show that the radiant energy reaching the ground from the reentering ejecta would be sufficient to ignite tinder, it would thereby spark widespread fires. The authors also review other evidence for and against the firestorm hypothesis and conclude that all of the data can be explained in ways that are consistent with widespread fires.
Source:
Journal of Geophysical Research-Planets, doi:10.1002/jgrg.20018, 2013
http://onlinelibrary.wiley.com/doi/10.1002/jgrg.20018/abstract
Title:
K/Pg extinction: Reevaluation of the heat/fire hypothesis
Authors:
Douglas S. Robertson: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA; William M. Lewis: Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA; Peter M. Sheehan: Department of Geology, Milwaukee Public Museum, Milwaukee, Wisconsin, USA; Owen B. Toon: Department of Atmospheric and Oceanic Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA.
fyi
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Bill_W says:
And what do you get when you burn things? CO2!!! The demon gas strikes again.
Probably should outlaw asteroid fires.
K-Pg? What was wrong with the widely accepted K-T?
It seems each “scientist” has to have a different theory.
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Theresa says:
I have heard that it was the Dekkan traps volcano eruption that killed them. Does that create Co2 as well?
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AleaJactaEst says:
Interestingly the only geologist on the paper was the third author. The KT boundary discussion (now I’m showing my age as I prefer the KT monika) is many years old. The related extinction event took several million years and this is shown in the fossil record. Global wildfires would have caused an immediate (in geological terms) fingerprint. One that does not exist in the said record.
I’ve only ever heard it called the K-T boundary. WTH is this new one for?
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darwin says:
I think they’re wrong. Recently scientists have uncovered fossilized SUV’s and coal fired power plants. The evidence is mounting that Global Warming controls everything.
How else could one get public monies?
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jim2 says:
You can see a CO2 spike ~ 66 million years ago in this stomata study. This study shows CO2 much higher in the past than now.
http://www.sonoma.edu/users/c/crocker/516-2011/300myr%20profile.pdf
I’m guessing people who deal with deep time are jealous of historians who affect BCE...
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Micula says:
A layer rich in carbon was recorded from the classic K/T (K/Pg) site at Stevn’s Klint in Denmark. It was referred to by Hans Joergen Hansen (Univ. Copenhagen) as the “grey chalk” and has been used by some researchers as evidence of the post impact fire storm. Detailed sedimentological analysis shows that the carbon content includes 1-2 micro diameter hollow graphite spheres, known only from volcanic glasses. The depositional period of the “grey chalk” has been calculated by H.J. Hansen as approximately 600 thousand years. As he once said on a field excursion, “If we could find the wood that burns that long, then the energy problems of the world would be solved.”
Maybe a clue.
Probably a paper somewhere.
this whole thing about how a one mile wide asteroid can somehow send dust into the air and cause a world wide ice age and now cause a planetary fire is such total crap
I’ll see if I can find the origin of the change.
More:
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Hypothermania says:
DaveF says:
March 27, 2013 at 5:46 am
So what killed those dinosaurs that lived in the sea?
Burning trees caused CO2 levels to increase, which caused sea levels to rise dramatically and they all died from vertigo.
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CodeTech says:
They also show that the mass of soot that could have been released from the impact site itself is far too small to account for the observed soot in the K-Pg layer.
Sure. The models show that. However, what other possibilities exist?
First, look at the current understanding of the Chicxulub impactor. It appears to have been about 6 miles in diameter, and left visible rings at 40 miles and 110 miles in diameter. An exceptionally thick layer at 4200 feet deep was part of the discovery, and there is displaced material that indicates a “kilometers high” tsunami, which is to be expected from such a powerful impact. Imagine that volume of water washing away in all directions, and be glad that nothing like this has happened recently. It seems likely that any combustible forest for a long way away would have been stripped bare and carried away.
Second, consider the incredible energy that has just been expended on the crust, sending ringing shock-waves around the planet like a bell had been rung. Any weak spot would soon be volcanic, and who’s to say just how much of the mantle was exposed? Was the crater a gaping, smoking hole for years afterward? We’ve seen just how much material is ejected from a single volcano (Pinatubo comes to mind, and Mt. St. Helens), just multiply that by an unknown but large number. The entire planet was likely blanketed by soot and ash as a direct result, and possibly for decades.
Third, we’ve now seen the Chelyabinsk event, recorded on video from multiple angles. That was a very high relative speed event, and I didn’t see any evidence of ground structures bursting into flames. Ejecta from the Chicxulub impact that cleared the atmosphere and came crashing back would not have the same kind of relative speed, thus less chance of igniting the forests (which were probably washed away).
I like playing “imagine if” games as much as anyone, but the conclusions I’m reading here seem like they’re all on the outside of probability. Nothing seems to take away the most likely current theory, that the extinction event was caused by dramatic and rapid cooling caused by the impact itself, not giant forest fires. Although I don’t doubt there were fires from the impact, and it’s nice that they measured all the soot.
One thing IS certain… we can theorize and hypothesize and imagine all we want, but NOBODY knows for sure exactly what happens when an impact of that magnitude occurs. And if we’re lucky, we never will.
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