Global Wildfires Did Not Kill The Dinosaurs

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5 December 2003

Global wildfires did not kill the dinosaurs

New research has revealed that thermal radiation, resulting from the impact of
an asteroid colliding with the United States 65 million years ago, was not
responsible for the extinction of dinosaurs and other land organisms.

The massive 65 million year old impact crater, Chicxulub, on the Yucatan
Peninsula in Mexico, was first located by Alan Hildebrand and co-workers in
1991. The discovery led scientists to conclude that large amounts of thermal
radiation released by the asteroid's impact would have raised ground
temperatures to around 1000 C, igniting globally extensive forest fires and
effectively boiling land organisms alive.

However, new NERC funded research, shows that although forest fires played an
important part in the latest Cretaceous and earliest Tertiary ecosystems, there
is no evidence that North America was engulfed by wildfires 65 million years ago.

The research team from Royal Holloway, University of London, was led by Claire
Belcher with co-workers Professor Margaret Collinson, Professor Andrew Scott,
and members of the Canadian Geological Survey and University of Calgary. The
team studied quantities of fossil charcoal from the Cretaceous-Tertiary (K-T)
boundary sediments from non-marine rocks across North America, to test the
hypothesis that extensive forest fires occurred as a result of thermal radiation
released by the impact. Details of the research will appear in the December
issue of Geology (volume 31).

The latest Cretaceous and earliest Tertiary rocks were found to contain an
average of 16.3% charcoal, but neighbouring K-T rocks showed only 1.75%. More
surprisingly, the K-T rocks also revealed considerable amounts of unaffected
plant remains, with some sites containing as much as 60% non-charred plant
fragments.

"If we assume that extensive wildfires consumed the vegetation across the North
American continent, it is hard to imagine a situation where so much plant
material remained un-charred. This does not support the theory that North
America was engulfed by wildfires at this time," said Claire Belcher, from Royal
Holloway's Department of Geology.

The revelations led Belcher's team to further question the amount of thermal
radiation released from the K-T impact. Spontaneous ignition of biomass occurs
at around 545 C and vegetation will begin to smoulder when subjected to
temperatures around 325 C. This suggests that ground temperatures cannot have
been greater than 325 C, and no more than 6 kW.m-2 of thermal power was
delivered to the ground for any significant length of time, compared with
considerably higher previous estimates of 5000kW.m-2 and 150kW. m-2 .

Art Sweet, from the Canadian Geological Survey and a co-worker on the project,
explains "It is recognised that major disruptions occurred in both plant and
animal communities at this time, but the new findings indicate that these are
not coincident with increased abundances of charcoal".

Belcher concludes, "The research we have carried out suggests that the amounts
of thermal radiation released by the impact of an asteroid with the Earth 65
million years ago, were not as significant as previously thought, and the energy
component of the K-T event was not responsible for the extinctions seen at this
time".

Belcher hopes that research may now focus on addressing other hypotheses, which
may explain the extinction patterns and disruptions seen at this time, including
the death of the dinosaurs.

ENDS

Editor's notes

Claire Belcher -- PhD student at Royal Holloway, University of London. Research
focuses on assessing the evidence for extensive wildfires at the K-T boundary.
Claire is keen to use the data collected on wildfires to address the amounts of
thermal energy released by the K-T impact. Other interests include the
preservation of wildfire in the fossil record. (Msc UCL, Micropalaeo, Bsc at
Royal Holloway, University of London, Geology)

Prof. Margaret Collinson -- Reader in plant palaeobiology. She also has a keen
interest in the K-T boundary particularly in the water plant Azolla that can be
found in and around the K-T boundary deposits across North America. She also
continues active research on plant palaeobiology including charred plant specimens.

Dr. Art Sweet specialises in palynology at the Geological Survey of Canada in
Calgary. He has researched the record of plants across the K-T boundary for many
years and has published considerable work on the Canadian K-T sites.

Dr. Alan Hildebrand has worked extensively on the K-T boundary, making one of
the largest contributions to this field in recent years by discovering the
Chicxulub impact crater. He still actively researches the K-T but is also
focusing on planetary geology and asteroid identification.

Prof. Andrew Scott specialises in coal geology and the Pre Quaternary history of
palaeo wildfires. He has probably researched and published more work than any
one else on palaeo wildfires.