Studying the ashes of the K-T event

[Phil Bigelow <bigelowp@juno.com>]

An additional question is how hot were these K-T boundary fires?

In *healthy* modern ecosystems, wildfires tend to scorch only the
uppermost 1-2 cm of the soil column, sparing the deeper roots and spores
and seeds and other soil biota (bacteria, soil insects, worms, etc.). 
Recovery to full diversity is very rapid (within a couple seasons),
because not only was the soil spared, but the high canopy was also
spared, leaving the tallest trees alive.  The wildfire literally "sweeps"
over the area, and flame temperatures remain relatively low.

But in modern ecosystems that are *not* healthy, the soil layer is topped
with a thick layer of fuel that has accumulated over many seasons (dead
leaves, pine needles, fallen trees, etc.), and it will burn very hot and
very deep into the soil column.  Deep-hot burns can literally sterilize
the soil column down to a half a meter, so that there are few remaining
biota left to reestablish themselves.  On slopes, loss of deep roots
usually leads to rapid soil erosion, which only exacerbates the problem. 
Deep-hot wild fires don't "sweep" through an area; instead they linger
for hours, building up heat, and burning the trees (even the high canopy
species).  Nothing is spared by a deep-hot.

See also:

Pyne, S. J., P. L. Andrews, and R. D. Laven. 1996. Introduction to
Wildland Fire (2nd edition). Wiley, New York, xxxiii + 769 p

Recolonization in an area that suffered a deep-hot wildfire must come
from spores and seeds blown in by the wind.  Unfortunately, soil bacteria
may take many years to return to a healthy percentage.  That is a major
problem in modern ecosystems, because without nitrogen-fixing soil
bacteria, certain key food plant species cannot grow (legumes, tubers, to
name a couple examples).  Legumes are a Cenozoic clade, but I suspect
that there were many Late Cretaceous plants whose roots also relied on
nitrogen fixing bacteria. (Kirk Johnson has found Cret. root fossils with
attached bulbous tuborosities.)

"Normal" wildfires = good for all living things.
"Deep-hots" = bad for everything in just about every possible way.

A lot of hypothesizing has been published in a lot of professional papers
on whether the K-T boundary fires were 1) indeed global in scope and; 2)
were "normal" wildfires or were "deep-hot" wildfires (see below). 
Unfortunately, not a lot of actual field work and data collection has
been focused on these two questions.  Most of the extant literature has
focused on ignition temperatures (which is mostly theory, I might add),
not on the actual wildfire dynamics.  Testability is the key, and the
evidence for *how* the landscape actually burned is still in the ground
waiting for someone to dig it up.   It would be a sweet project for a PhD
student who is currently looking for dissertation ideas.

Not that I want to write someone's dissertation proposal for them, but
here are a few starting refs. to get the sooty ball rolling:


Pyne, S. J., P. L. Andrews, and R. D. Laven. 1996. Introduction to
Wildland Fire (2nd edition). Wiley, New York, xxxiii + 769 p.

Belcher, C. M., M. E. Collinson, A. R. Sweet, A. R. Hildebrand, and 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.

Durda, D. D., and D. A. Kring. 2004. Ignition threshold for
impact-generated fires. Journal of Geophysical Research 109: E08004.
[on-line version of the journal].

Gilmour, I., W. S. Wolbach, and E. Anders. 1989. Major wildfires at the
Cretaceous-Tertiary boundary, in Clube, S. V. M., ed., Catastrophes and
evolution: Astronomical foundations. Cambridge Unversity Press,
Cambridge, p. 195-213.

Jones, T. P., and B. Lim. 2000. Extraterrestrial impacts and wildfires.
Palaeogeography, Palaeoclimatology, Palaeoecology 164: 57-66.

Kring, D. A., and D. D. Durda. 2002. Trajectories and distribution of
material ejected from the Chicxulub impact crater: Implications for
postimpact wildfires. Journal of Geophysical Research 107:6-1 - 6-22.

Melosh, H. J., N. M. Schneider, K. J. Zahnle, and D. Latham. 1990.
Ignition of global wildfires at the Cretaceous/Tertiary boundary. Nature
343:251-254.

Robertson, D. S., M. C. McKenna, O. B. Toon, S. Hope, and J. A.
Lillegraven. 2004. Fireball passes and nothing burns: Comment. Geology 32

Tinus, R.W., and D.J. Roddy. 1990. Effects of global atmospheric
perturbations on forest ecosystems in the Northern Temporate Zone:
Predictions of seasonal depressed temperature kill mechanisms, biomass
production, and wildfire soot mechanisms, in Sharpton, V.L., and P.E.
Ward (eds.), Global catastrophes in Earth history. Geological Society of
America Special Paper 247: 77-86.

Wolbach, W.L., I. Gilmour, E. Anders, C.J. Orth, and R.R. Brooks. 1988. A
global fire at the Cretaceous/Tertiary boundary. Nature 334: 665-669.


Lastly, Uncle Phil's got a little poem for the kids on the List:

        CHARCOAL-SCHMARCOAL

Charcoal ain't the same as coal.
On that, I'll bet my soul.
The two can be discriminated by a geologist who ain't intimidated.
Charcoal has lost some stuff, while coal is nearly whole.

Dinosaur-age fires certainly ain't a bore.
Who wouldn't pay to see a flash-fried pterosaur?
The fires charred the roots,
and the smoke created the soots
that made K-T breathin' a heck of a chore.

Porous soot particles!
Non-porous soot particles!
Convection-lofted charcoal embers!
Each has a unique scientific meaning
to Geological Society of America members.

<pb>
--


On Sat, 12 Nov 2005 20:21:53 +0100 Tommy Tyrberg
<tommy.tyrberg@norrkoping.mail.telia.com> writes:
> 
> 
> Jerzy Dyczkowski wrote:
> 
> 
>  >Finally - one day after fire, plants begin to regrow
>  >providing food. I assume dinosaurs could survive some
>  >weeks without food (and eggs might much longer).
> 
> It's not that simple. The early successional vegetation after a fire 
> is 
> very different from what came before ("fern spike"). It normally 
> takes at 
> least a century before the vegetation is back to climax. If the fire 
> is in 
> a habitat where fire does not occur naturally (e. g. rainforest) the 
> 
> vegetation may NEVER return to the original state since many species 
> will 
> not have seeds that survive long enough.
> 
>  >Of alternative theories: amphibians and freshwater
>  >fish are very suspectible to acid rain. Small birds
>  >are very suspectible to smoke (use of canaries in coal
>  >mines). In modern forest fires, birds drop dead from
>  >smoke.
> 
> Actually it is methane canaries are used to detect. Incidentally 
> many birds 
> are attracted by fire. For example I've several times seen raptors 
> hunt 
> insects and small animals flushed by brushfires in Australia, they 
> don't 
> seem to be much discommoded by the smoke.
> 
>  >I would first ask some meteorologist/astronomer. How
>  >would real atmosphere react? Would falling microscopic
>  >ejecta indeed deliver single heat pulse? I suggest
>  >atmospheric currents would produce uneven fall and
>  >evaporating water would quickly block radiation from
>  >reaching ground. This I don't know. Nor I see
>  >discussed there.
> 
> Atmospheric currents are completely irrelevant to ballistic objects. 
> The 
> infall would indeed be uneven, but this is because the debris is not 
> 
> ejected evenly from the impact site.
> Evaporating water would indeed block radiation if it forms clouds. 
> This 
> requires cooling - which can't happen when there is intense 
> irradiation 
> from above.
> 
> 
>  >I think this means that. Heat needed to kill large
>  >animals would also dry surrounding vegetation and
>  >start a fire (actually fire would burst first, due to
>  >heat capacity of big animal).
> 
> Nonsense. Animals will die (of burns and/or heat stress)long before 
> e. g. 
> wood catches fire. Wood will start burning when the surface is 
> heated to ca 
> 300-400 degrees centigrade. Most animals won't survive having their 
> skin 
> heated much over 100 degrees centigrade.
> 
>  >they list avian lineages surviving KT and duly
>  >say that many DON'T contain any burrowers.
> 
>  >In most of remaining clades, burrowing is restricted
>  >to few derived taxa so likely evolved recently. This
>  >applies to eg. ratites (kiwi).
> 
> First remember that we really know very little about Cretaceous 
> crown-group 
> birds since there are almost no fossils. Nesting and sheltering 
> habits of 
> ghost-lineages are not easily determined!
> Note however that in anseriforms some of the most plesiomorphic 
> extant 
> forms (tree-ducks) are hole-nesters as are a few species of tinamoes 
> (the 
> most plesiomorphic paleognaths, crevice-nesters might be a better 
> term in 
> this case). Passerines are probably primitively hole-nesting etc. 
> The only 
> real problem as I see it are the galliforms which does not contain 
> any 
> hole-nesting species today (though some galliforms do make 
> snow-burrows).
> 
>  >Nitpicking, on top of this they lump hole nesting with
>  >burrowing. In this case, tree hole is no protection
>  >from heat radiation enough to ignite a whole tree.
> 
> See above. Essentially every unprotected animal would be dead long 
> before a 
> whole tree catches fire.
> 
> Tommy Tyrberg
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 


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