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Re: Why was Earth a fiery hell 55 million years ago?



--- Dora Smith <villandra@austin.rr.com> schrieb:

> Well, I'm trusting it was temporary.   The point was
> that Earth's geology 
> and chemistry are very changeable.
> 
> I think the question would be how do we know what
> exactly happened with 
> foraminifers and corals in this time.   Logically
> the record of what 
> happened to them must be in the fossils of these
> creatures.   Logically 
> also, they died back but did not go extinct.

That's the oddball here: there are few enough fossils.
But on the other hand, the PETM was geologically
short, a few 100.000 years at most. Obviously corals
and foraminifers didn't go completely extinct, and the
reason may be that as opposed to K-Pg, the PETM was
not catastrophic - the killer was an endogenous
process that built up over some time. Volcanos or
bolide, whatever it was - that was only the trigger.

The methane clathrate hypothesis is attractive,
because it explains all the extra carbon that suddenly
starts to appear in the atmosphere.

Though there must have been refugia for corals
somewhere, it's hard to say where exactly - much of
the fossil record was just dissolved away, and apart
from a rough latitudinal zone one can guesstimate, the
problem is that the ocean currents might not have
followed the usual pattern as sea temperatures and
seawater chemistry apparently were affected beyond the
continental shelf.

If one would plot extinction levels at a finer scale,
the K-Pg event would probably turn out to have caused
most extinctions initially, whereas in the PETM they
built up gradually: any organism would have gotten
some 1000s of generations of advance warning. Whereas
the time from when you knew something was wrong to
impact at the K-Pg event was hours at most.

Not having read anything about coral phylogeny, I
wonder: would such an event not mess up the molecular
data? As opposed to K-Pg, where apart from "being in
the right place" (say Antarctica) and "not being too
high up in the trophic web" there was little to assist
any taxon in surviving, PETM was a much more nonrandom
selective force. In birds for example, many species
probably went extinct, but very few major lineages
seem to have disappeared. Even diatrymas which from
their inferred life history traits would not have been
very resilient to such pressure survived.

In short, the picture is such that the PETM over some
time stretched life on earth - and the climate - very
much to the breaking point, but did not actually break
it. Whereas K-Pg, in "one fell stroke" (Tolkien I
think) did break it.


Eike


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