Re: Pollen From Permian/Triassic Extinction Show UV Induced Mutations

["Colin McHenry" <cmchenry@westserv.net.au>]

-----Original Message-----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Date: Monday, 20 October 2003 3:09
Subject: Re: Pollen From Permian/Triassic Extinction Show UV Induced
Mutations
> >
>> > OK. But then we need at least 2 causes for the P-Tr mass extinctions.
>>
>> IIRC Erwin mentioned anoxia.
>
>Which can be produced by an impact -- if it stirs up enough methane. BTW,
if
>enough methane gets high enough into the atmosphere, it will destroy the
>ozone layer, though not catalytically like nitrogen oxides.



Hi David,

Apologies if you already know about this, but there was a BBC Horizon
program about this last year.  The URL is
http://www.bbc.co.uk/science/horizon/2002/dayearthdied.shtml - you can link
to the transcript from that page.

It actually wasn't as bad as I had expected.  They ended up concluding that
the extinction 'event' was a two stage process - a period of volcanism
induced global warming (over a period of about 40 - 50,000 years) which
evalated temperatures enough to mobilise marine methane hydrate deposits
into the atmosphere, causing a second period of (very quick) warming.   They
mentioned that the first wave of extinctions were mainly terrestrial, but
that the second affected the marine systems first, and then spread to
terrestrial systems. (I think that this is based upon Wignall's data from
Greenland). They seemed to think that the combined effect was an average 10
deg rise in temp over an 80,000 year period.

The weakest part of the program, to my mind, was that the reconstructed
global temperature rises for the volcanism alone was put at 5 deg, and this
was pronounced (with no supporting evidence or logic of any kind) to be
insufficient to cause an extinction of that scale.  However, combined with
the warming caused by the methane hydrate, it reached the magic figure of 10
degs, which apparantly _is_ enough to cause a P/Tr scale extinction.  What
research these figures are based upon they did not say.

By the way, the P/Tr boundary outcrops about 30 kms from my house, as part
of the Newcastle Coal Seams.  The underlying P is a coal, the Tr immediately
on top of the boundary is a channel/floodplain deposit from a lower stage
river.  The only difference, in terms of the depositional environment, seems
to be the absence of plant matter in the Tr rocks.  It doesn't look very
regressive, but I'm sure there's been some proper work on it somewhere.

Cheers
Colin

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Colin McHenry
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