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Much of my work on the K-T extinctions has involved searching for
mass extinction killing mechanisms whose evidences are preserved in
the geobiological record. Much of that work involved searching for
evidences of a K-T impact winter, and global impact-induced wildfires
that theoretically consumed most of earth's forests.
My post of Sat. 10 Jan 2004 10:07:57 cited my paper, "Impact Winter
in the Global K-T Extinctions: No Definitive Evidences" (in Levine,
J. S., ed., _Global Biomass Burning: Atmospheric, Climatic, and
Biospheric Implications_, Cambridge, MIT Press, 1991, p. 493-503).
That paper was the culmination of a nearly 10 year search for
evidences of an impact triggered dust-induced "impact winter" (global
dust-induced blackout and refrigeration) that began with the 1980
publication of the Alvarez impact theory.
Recall that the theoretical global blackout purportedly triggered
extinctions among plants that served as food for herbivorous
dinosaurs, thus causing extinctions among the herbivores, and then
among predatory dinosaurs that used the herbivores as a food source.
That paper also included a search for evidences of theoretical K-T
global wildfires that burned most of earth's forests via sparks and
radiation from a K-T impact as proposed by Wolbach and others.
I found no definitive evidences for either a K-T impact winter or
global wildfires. Now, two recent papers seem to support my work.
The first is Kevin Pope's paper, "Impact dust not the cause of the
Cretaceous-Tertiary mass extinction" (Geology, 2002, v. 30, pp.
99-102). Following are some quotations from Kevin's paper:
"These findings indicate that the original K-T impact extinction
hypothesis--the shutdown of photosynthesis by submicrometer-size
dust--is not valid, because it requires more than two orders of
magnitude more fine dust that is estimated here."
"These results shed doubt on the importance of impact dust in the
mass extinction that marks the K-T boundary. A global atmospheric
loading of...submicrometer-sized dust would not cause the
catastrophic impact winter often proposed...."
Kevin did leave open other impact hazards such as global cooling
caused by impact production of sulfate aerosols, and soot from global
The second is the Belcher et al. paper, "Fireball passes and nothing
burns--The role of thermal radiation in the Cretaceous-Tertiary
event: Evidence from the charcoal record of North America (Geology,
2003, v. 31, pp. 1060-1064). Following are some quotations from the
"The K-T and lowermost Tertiary sedimentary rocks of six nonmarine
sequences (Colorado to Saskatchewan) contain no charcoal or
below-background levels of charcoal and a significant quantity of
noncharred organic materials, revealing that there was no distinctive
wildfire across the North American continent related to the K-T
"Therefore, the thermal power delivered from the impact to North
America did not have the destructive potential previously predicted.
High amounts of thermal radiation were not responsible for the
environmental perturbations or extinctions associated with the K-T
With the seemingly virtual elimination of a K-T impact winter, and
global wildfires, not many potential mass extinction killing
mechanisms remain. A couple contenders are climatic cooling via
impact-induced injection of sulfate aerosols into the atmosphere, and
greenhouse warming via a combination of several factors.