[meteorite-list] Global Wildfires Did Not Kill The Dinosaurs

From: Charles Viau <cviau_at_meteoritecentral.com>
Date: Thu Apr 22 10:17:43 2004
Message-ID: <000a01c3bf9c$6366f100$1800a8c0_at_chupa>

Hi list,

Alan Heldebrand (discoverer of Chix.) did not believe that a global
wildfire was possible either. In one of his papers he cited the work he
did with C.Belcher a few years ago:

(Quote, reproduced without permission)

"Belcher et al. (submitted) have established that no charcoal occurs in
the soot-bearing boundary layers at nonmarine sites in North America.
This apparently indicates that the thermal pulse from re-entering ejecta
mechanism is not capable of igniting the forests even relatively near
Chicxulub, relegating this mechanism a very minor role at best, as
fireball irradiance will dominate thermal effects close to the crater."

They published a table (with original work done also by W. Wolbach) that
made so much sense. It showed the increasing agents of environmental
damage that would be caused by such an impact. Certainly not being an
expert at any of this, is seems reasonable to me that ALL large impacts
impart the same general environmental destruction in a similar
increasing scale.

(table, partly reproduced without permission)

Environmental change agent Duration Reference(s)

1. Dust veil (darkness and cold) Months
2. Proximal wind
Hours
3. Proximal giant waves Hours,
4. Proximal to regional fireball irradiance Minutes
5. Regional thermal pulse from re-entering ejecta Hours
6. Acid rain (nitrogen- and sulfur-based) Years
7. Stratospheric aerosols (cold) Decades
8. Ozone layer depletion (ultraviolet exposure) Decades
9. H2O greenhouse Decades

10. CO2 greenhouse
Millennia
11. Poisons and mutagens Years to
millennia?
12. Oscillatory/disrupted climate Million
years

I love the subject, and especially in this case, believe that a global
wildfire would require much more energy. (perhaps the size of what might
have hit Hudson bay?)

-----Original Message-----
From: meteorite-list-admin_at_meteoritecentral.com
[mailto:meteorite-list-admin_at_meteoritecentral.com] On Behalf Of Sterling
K. Webb
Sent: Wednesday, December 10, 2003 9:22 PM
To: Ron Baalke; Meteorite Mailing List
Subject: Re: [meteorite-list] Global Wildfires Did Not Kill The
Dinosaurs

Hi, All,

    In a wildfire more immense than our wildest dreams, there will be
large amounts of
unburnt vegetation IF the fire consumes enough oxygen over a wide enough
area that the
"local" oxygen level drops below the level required to sustain
combustion at the
ambient temperature of the fire.

    Back in the 70's, several planetologists suggested that the Earth's
oxygen levels,
which were then thought to have stayed relatively constant, were in a
feedback cycle,
the upper bound of which was set by the calculation that at oxygen
concentration of
over 24%, fires would break out spontanteously, burn off large areas of
the planet and
lower the concentration.

    Those calculations are now suspect, and we now know that oxygen
concentrations have
varied more widely than we thought. There is evidence that the
Cretaceous levels were
30%. I wonder what oxygen level was assumed in this study? It could make
a big
difference.

    You can still burn off a world without resorting to direct thermal
radiation; just
blast hot materials all over an Earth with too much oxygen for its own
good.


Sterling K. Webb
------------------------------------------------------------------------

---
Ron Baalke wrote:
>
>
> Global wildfires did not kill the dinosaurs
> 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.
>
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Received on Wed 10 Dec 2003 11:08:03 PM PST