

Dinosaurs broiled, not grilled - araneae
http://sciencenews.org/view/generic/id/50691/title/Dinosaurs_broiled,_not_grilled

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electromagnetic
The original assumption that 20 minutes at ~260 degrees could cause worldwide
forest fires is a far jump to begin with. Cut a section out a tree and place
it in an oven set at ~260 for 20 minutes and you'll have nothing more than a
mildly warm piece of wood, you'll definitely be a long haul from spontaneous
ignition.

I've had plenty of camp fires in my time, and fresh wood certainly takes its
time before combustion. I have serious doubts that a living tree would be
capable of spontaneous ignition within 20 minutes of exposure to heat.

It may have ignighted forest fires in some dry or drought areas, but you're
unlikely to spread forest fires in the boreal forests, where wildfires would
have had the greatest effect. Forest fires in these regions happen only every
20-200 years, it's unlikely the raise of temperature in these regions would
have caused a wildfire in the height of summer if it wasn't reaching one of
these periods anyway. If the impact occurred during the winter months you'd
have no chance to cause wildfires in these regions, even if the planetary
temperature jumped by 260 degrees, the boreal regions would likely still be
20-30 degrees _below_ the ignition point of wood. Considering these places can
be 10+ feet deep in snow and ice (which incidentally insulate from heat) there
likely wouldn't have been a noticeable effect.

Considering winter in the boreal lasts 5-6 months, there was a 50/50 chance
that the impact would only have a negligible effect. Then consider the fact
that the boreal has a high density of bogs and lakes means the wood is
frequently waterlogged, so the chance of boreal wildfires being ignited
gradually become slim-to-none, especially if it was a cold period in the
climatic cycles.

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mbrubeck
For us Americans, note that 260° C = 500° F. I haven't tried the experiment,
but given how quickly various foods (including fresh rosemary sprigs and other
live plant matter) blacken in an oven that temperature, I wouldn't be
surprised at all if it set leaves and small branches on fire in less than 20
minutes. The smaller branches could then act as kindling for larger ones. Good
points about water and ice, though. I'm curious now to see the assumptions in
the old models. How much fiery molten rock raining from the sky does it take
to melt and evaporate a heavy layer of snow?

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electromagnetic
Agreed, kindling would easily set on fire, and assuming a heavy density it
could certainly start a forest fire. However, the effect would be no different
than dropping a cigarette. When you get to that hair-trigger it's going to
happen anyway. I assume the disaster is in the 'global' forest fire that would
have ensued, keeping temperatures higher than habitable in major areas of the
planet and then producing a cooling effect due to the soot emitted.

However, from my experience soot is emitted more by poor burning not good
burning, so could the soot layer that was laid down have been made by a big
poor-burn of fuel, rather than a major forest fire. I've seen people burning
damp leaves and it emits huge plumes of soot.

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theli0nheart
How come the researchers don't research the possibility that the soot coughed
up by the asteroid impact blocked light from reaching Earth and led to drastic
cooling? Temperatures in the dinosaur days were pretty high relative to now,
so it doesn't seem far fetched to me that they died of cold, and not heat.
This theory also explains why smaller animals survived, especially mammals
(hair is a good insulator).

~~~
yannis
The cooling effect is more possible and can also account for extinctions in
the oceans as well. After the Krakatoa eruption for years the world had a
cooler climate.

