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.
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I think another factor in the mass extinction could have been destruction of the ozone layer and radiation burning and cancer to animals without thick fur/feathers, or nocturnal or underground habits. Note that the reptile survivors were snakes, alligators, turtles, etc. which all tend to use burrows or are small and can hide. Birds and mammals, feathers, fur, live in trees or jungles, or hide in burrows or were small.
Burrowing species had an advantage over other land creatures because of availability of water, soil critters (insects, worms, etc) and cover (all foliage vanished); marine species were mostly selected by size.
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