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The dinosaurs did not die in fire, from the latest Geology



Greetings,

The latest issue of Geology has a paper that confirms what most people who
know something about terrestrial sedimentology have suspected for a while:
that the evidence for a global forest fire at the K/T event is dubious at
best.

The authors conclude that reduced insolation forming an "impact winter", and
possibly increased rains, extensive cloud cover (again, decreasing incoming
sunlight), and a brief thermal pulse would be more likely killing agents
from the extinction.

It should be noted that the original Alvarez scenario was extinction through
decreased insolation; global forest fires and super acid rain and the rest
of the ILM Special Effects were added by later work.

In any case, here's the paper reference and abstract:

Belcher, C.M., M.E. Collinson & A.C. Scott. 2003. Fireball passes and
nothing burns?The role of thermal radiation in the Cretaceous-Tertiary
event: Evidence from the charcoal record of North America. Geology 31:
1061?1064.

ABSTRACT

High soot contents have been reported in Cretaceous-Tertiary (K-T)
sedimentary rocks, leading to the suggestion that the amount of thermal
power delivered from the Chicxulub impact was sufficient to have ignited
wildfires. Soot cannot be used to indicate fire location, however, as soot
from one large fire could spread globally. Sources other than biomass
burning could also yield soot. Charcoal in nonmarine sedimentary rocks (here
quantified in situ in polished blocks) provides a unique tool to record the
distribution of wildfires and therefore assess the extent of any thermal
radiation associated with the impact at Chicxulub. 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 event. This finding indicates that the K-T impact cannot have
delivered a peak irradiance of >95 kW·m-2 of thermal power to the atmosphere
and <19 kW·m-2 to the ground. 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
event.


                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796