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

["David Marjanovic" <david.marjanovic@gmx.at>]

> >Absence of evidence is no evidence of absence.
>
> Erwin wrote that an impact big enough to trigger massive volcanism

Why should an impact trigger volcanism, both in general and at the P-Tr???

> should definitely have left evidence comparable to that around the K-T.
The same applies to an impact big enough to have caused extinction of such
magnitude.

Not terribly much research has been done. And, for example, if it was a
comet, we won't find so many extraterrestrial trace elements as we do in the
K-T boundary layer; and if there was no quartz in the impact site, we won't
find shocked quartz...

> > > > Constrained to 8,000 years or less by cyclostratigraphy (on the
mountain
> > > > called Gartnerkofel in Austria, you can see the Milankovic cycles in
the
> > > > sediment), according to Rampino.
> > >
> > > Up to 50,000 in the Karoo basin.
> >
> > I don't know, but I bet that the resolution of those terrestrial
sediments
> > is much coarser than that of marine sediments which are fine enough to
> > record Milankovic cycles.
>
>  Still appears way too long for an impact.


8,000 years is the smallest amount of time that can be resolved on the
Gartnerkofel. It is a pixel, sort of. It isn't possible to tell apart 8,000
years from 8,000 seconds on that mountain.

> > > > Then why was there a fungal spike? (Globally!)
> > >
> > > Earlier extinction on land.
> >
> > 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.

> >This sounds like they didn't exclude the Signor-Lipps effect... smaller
ones
> are easier to overlook...
>
> They mentioned three smaller taxa.

Three? That's very, very few. How many big ones did they find?

> > And what could have killed off animals with small
> > adult size but not small juveniles of bigger species?
>
> Competition for certain scarce resources (e.g. water and shade, perhaps)
may have favored larger taxa,

But not their juveniles. And needless to say, this wouldn't explain the mass
extinction itself, as opposed to the supposed decline before it.

> Juveniles may have been vulnerable for a time-if adults could not assist
them somehow, maybe by shading them-

Why do you assume parental care in dicynodonts _and_ pareiasaurs _and_
gorgonopsians _and_ what do I know what else?

> > > > Global synchronous aridity would be needed for that
> > > > -- and why should that happen?
> > >
> > > Maybe regression reached a certain threshold where habitat
> > > loss/fragmentation occurred.
> >
> > But globally?
>
>  Depends on the extent of regression.

There would still be coasts left -- a regression can at best explain
regional but not global extinction. And not everything needs floodplains.

> It wasn't necessary for every acre to dry up to cause extinction; it
depends on how much continuous wet habitat was needed.

Yes. And why should _all_ those diverse taxa need wet habitat?

>  I don't know. In South Africa the replacement of dicynodonts etc with
Lystrosaurus has been linked to a drier climate e.g. more drought tolerant
plants.

"Has been linked" implies a hypothesis, not a fact. :-) We don't know what
habitat, if any, *Lystrosaurus* preferred, nor do we know what greenery, if
any, it preferred. And do we known that *Dicroidium* was more
drought-tolerant than *Glossopteris*? Or perhaps *Glossopteris* just so died
out (e. g. by means of a mass extinction, global wildfires & stuff), so, due
to lack of competition, *Dicroidium* was able to everywhere instead just of
in the dry areas to which it was adapted?