From the AGU:
Global fires after the asteroid impact probably caused the K-Pg extinction
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.
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Few days ago I was looking at some geomagnetic anomalies across Siberia, then I looked at Google Earth and saw a spectacular feature about 9-10 km across
http://www.vukcevic.talktalk.net/SiberiaRose.htm
I am not aware of any references to it
Geologists, any ideas ?
Doug Proctor says:
March 27, 2013 at 8:20 am
No central uplift peak?
Okay, I’m fussy about the painting. It’s science. We’re supposed to be fussy.
An impact that big would send a tsunami up the Cretaceous continental sea from the Gulf of Mexico to the Arctic, one would think. I live in Alberta; out at Drumheller, you can see the Cret-Tertiary boundary in the valley wall (just above the last dark line of a coal stringer). It holds, apparently, the Iridium layer of Alvarez. However, no tsunamic debris OR (more signficantly) an erosive surface.
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Doug IIRC, a structure that looks like the result of a major tsunami near the KT boundary was identified in Texas a number of years ago. If the KT boundary at Drumheller is above a coal bed, doesn’t that suggest that the land there was above sea level at the end of the Cretaceous? I’m not sure how far inland the water from even a very large tsunami will penetrate. Many tens of kilometers I should think, but maybe not many hundreds?
Everyone knows “mass extinctions” begun just as prehistoric politicians emerged from the primordial slime!
Will a fern burn with pure oxygen? Has anyone tried it? That would be the first thing to establish in postulating extinction by fire. Is it possible to burn down a palm grove? Of course a conifer forest would burn up in 30% O2. Global fire? Seems like unadulterated nonsense. For capable consideration see Wiki:
http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event
–AGF
So was it purely inelastic collision?
” wws says:
March 27, 2013 at 9:01 am
“What’s the chances of the big one hitting right on the Cretaceous /Tertiary boundary, eh?”
I knew a girl once who thought it was amazing that so many American Civil War battles, like Gettysburg, happened to get fought in National Parks.”
Isn’t like wondering why all the deer are starting to use the deer crossing areas on our highways now?
???
Is there enough oxygen in the earth’s atmosphere to support a world-wide firestorm?
Yes. Plenty.
Mass of the atmosphere 5.1*10^18 kg.
So mass of Oxygen in atmosphere is about 1.2*10^18 kg.
Biomass of Earth = 560 billion tonnes = 5.6*10^14 kg.
So there appears to be about 2000 kg of O2 for every kg of biomass. A world-wide firestorm won’t be starved by a lack of oxygen.
Question and hypothesis:
I accept the Yucatan asteroid theory.
I suggest that the entire gulf of Mexico is also an asteroid,, albeit an even older asteroid, impact zone.
Has anyone else thought this. Seems obvious to me.
Jimbo says:
March 27, 2013 at 9:17 am
Just 5 days ago I read this:
BBC 22 March 2013
Dinosaur-killing space rock ‘was a comet’
“You’d need an asteroid of about 5km diameter to contribute that much iridium and osmium. But an asteroid that size would not make a 200km-diameter crater,” said Dr Moore.
“So we said: how do we get something that has enough energy to generate that size of crater, but has much less rocky material? That brings us to comets.”
http://www.bbc.co.uk/news/science-environment-21709229
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Thanks, Jimbo. I missed that. Here’s the conference presentation:
http://www.lpi.usra.edu/meetings/lpsc2013/pdf/2431.pdf
But then, too, there’s this hypothesis from Feb:
http://phys.org/news/2013-02-group-chicxulub-crater-binary-asteroids.html
The K/T is still making waves.
Vukcevic, sounds like a good field trip.
CodeTech says:
March 27, 2013 at 6:26 am
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).
———-
Chenlyabinsk event was a single object. After the Chicxulub impact there would have been 10’s of millions, perhaps billions of objects re-entering the atmosphere.
If the IR was sufficient to ignite tinder, it wouldn’t have been to healthy for any animal caught out in the open at the time. First and second degree burns over the entire top side of the animal.
wsbriggs says:
March 27, 2013 at 6:49 am
The ionization radiation created from the passage of the object through the atmosphere
—
How pray tell does an object plowing through the atmosphere cause atoms to fission?
Blade says:
March 27, 2013 at 7:59 am
—
Most fires only burn a small portion of a forest or grassland. These fires would have taken out the entire forest/grassland.
Animals normally escape fires by running from them. (Plus the fact that most animals aren’t where the fires are). When the whole world is burning, where do you run to?
Jimmy Haigh. says:
March 27, 2013 at 8:01 am
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I read somewhere that the KT boundary layer is thickest in the southeast US and Carribean. And is thicker throughout N. America than it is in Europe and Asia.
wws and John Tillman.
You guys got it.
Paul Westhaver says:
March 27, 2013 at 9:57 am
Question and hypothesis:
I accept the Yucatan asteroid theory.
I suggest that the entire gulf of Mexico is also an asteroid,, albeit an even older asteroid, impact zone.
Has anyone else thought this. Seems obvious to me.
******************************************************************
Yes, someone has. Canadian geologist Michael Stanton thought of it two decades ago, but only published his idea in 2002. He accounts for the Permian-Triassic extinction ~250 Ma by this proposed impact, citing the Louann Salt as evidence. The hypothesis has not garnered much support. The odds of two major craterings in the same area ~185 million years apart doesn’t really enter into it.
http://www.aapg.org/explorer/2002/12dec/gom_impact.pdf
Doug Proctor says:
March 27, 2013 at 8:20 am
—
There probable was a central peak, however because of the depth of the crater, there was no solid ground underneath the peak to support it, and it sank back into the earth.
The studies I have seen put the size of the tsunami at a couple of kilometers. No way that exends more than a few hundred miles inland. Not all the way to the arctic
tty says:
March 27, 2013 at 8:45 am
“I’d like to know if the authors of this paper mapped out possible ejecta trajectories. The trajectories vary with the impact velocity and direction of course. My best guess, and it is a guess, is that very little of the ejected material was likely to make it to Australia, South and East Asia as I think that the vast majority of possible trajectories bring the material down rather quickly on the half of the planet centered on the impact site. Fires on that side? Seems quite plausible. Fires of the opposite side? Not so much I’m thinking.”
Contrariwise. This has been studied and is fairly well understood. The largest concentration of secondary impacts will actually occur near the antipodal point of the impact (this is pretty obvious if you think about trajectories a bit).
===========
Well actually, I DID think about the trajectories a bit, and I don’t think your scenario is obvious at all. To be honest, it doesn’t seem especially likely either. AFAICS, any ejecta that is travelling at less than orbital velocity (roughly 8km/sec) and most that is “launched” at angles below about 45 degrees will impact in the “impact hemisphere”. As will any material launched more or less straight up although that will presumably trail out to the West of the impact point as the Earth turns. Unless one assumes that ejecta are mostly traveling very fast and are mostly “launched” at high but not vertical angles, not all that many are coming down on the “back side”. However, I admit that I didn’t give any consideration to the distribution of ejecta velocity and elevations and assumed something sort of random — which is surely wrong. I don’t suppose you have a reference or two?
@Paul Westhaver
…I suggest that the entire gulf of Mexico is also an asteroid,, albeit an even older asteroid, impact zone…
When you come to think about it, EVERYWHERE on Earth was an impact zone at some point…
Has anyone else thought this. Seems obvious to me.
There are some suggestions that there were multiple impacts causing the KT event. Chicxulub
may or may not be the largest. There is a proposed impact structure just off the west coast of India, which may or may not be connected to the Deccan Traps event. And the argument continues as does the data gathering. Cheers –
http://www.currentscience.ac.in/Volumes/101/12/1525.pdf
http://news.nationalgeographic.com/news/2009/10/091016-asteroid-impact-india-dinosaurs.html
commieBob says:
March 27, 2013 at 8:58 am
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It’s not even close to being plausible.
John Tillman, thank-you for the citation. You made me very happy.
When I look at the Gulf of Mexico, it looks like the superposition of an ancient double hit, then the later Yucatan hit.
The Island of Cuba appears, to me, to be impact zone ejecta, as if the asteroid hit traveling south east obliquely to the planet. The impact would push up most of Florida and leave Cuba behind in the splatter zone.
That is complete speculation on my part.
If an approaching asteroid broke apart as it approached earth, then you could get a double hit effect. Again, mere speculation on my part and I do not possess the tools or expertise to test the idea.
When I learned of Pangaea as a child and tried to fit the continents together like puzzle pieces, the Gulf of Mexico always proved to me that a piece was missing.
Thanks
Just because a feature is roughly circular is not proof that it was caused by an impact. Other evidence includes fractured crustal rocks inside the “crater”. This doesn’t exist for the Gulf of Mexico.
Neither the Chicxulub impact nor the Deccan Traps volcanism were the primary extinction mechanism at the K-T boundary.
The fact that birds were little affected discounts the impact causation. The fact that all marsupials went extinct in N. America is another bit of evidence.
However, the marsupial extinction supports the theory that surface gravity increased rapidly at the K-T interval as well as the extinction of all marine reptiles and ammonites. Dinosaurs were diminishing in numbers as well as size millions of years prior to the K-T interval.
The Gravity Theory of Mass Extinction (http://www.dinoextinct.com/page13.pdf) is the only viable theory.