From: salem@pangea.Stanford.EDU (Bruce Salem)
Newsgroups: talk.origins
Subject: Re: Permo/Triassic quandary
Date: 7 Jan 1993 04:45:33 GMT
Organization: Stanford Univ. Earth Sciences
NNTP-Posting-Host: pangea.stanford.edu

In article <1993Jan6.212932.14558@nsisrv.gsfc.nasa.gov> jgacker@news.gsfc.nasa.gov (James G. Acker) writes:
>	Part two first:  From the abstract, it appears that Oberbeck
>believes what would be called (on the moon) a cratering episode could
>have influenced Godwana-tectonics.  Repeated multiple impacts are a possible
>cause of fracturing, rifting and flood volcanism -- hence the formation of
>continental crust, climate change, and ecosystem alteration.

	I am willing to suspend judgement on such a hypothesis to let
evidence accumulate yea or neigh on the cause of the breakup of Gondwana.

	One thing I have either forgotten or had wrong is the timming of
some mass extinctions, in particular the one that ends the Paleozoic,
the permo-triassic, and certian plate tectonic events. It is suggested
here that the permo-triassic extinction coinsides with the break up of
Gondwana and the effect of that is the disruption of habitat by tectonic
events and volcanism. I may have mistakenly said that a mass extinction
is timed with the formation of Pangea, much earlier. If a mass extinction
is linked with the formation of a supercontinent, it would have to do
with much loss of productive lowland and near-shore environments and the
relative emergance of the resulting continental mass. Breakup of a
large continent with the resulting flood basalts would disrupt many
habitats. I am alos aware the Oberbeck's proposal combines two
competing theories, one that says that it was volcanism, the kind
that produces flood basalts, trapps and the Deccan plateau, and the
other which uses asteriod impacts, for the cause of mass estinctions.

>	Now Part One:  I was chastised some months earlier for believing that
>catastrophic extinctions, whatever their actual cause, were unique
>events with a low probability.  It turns out that the extinctions are
>NOT unique or rare (David Raup has written a book on this), but the mechanisms
>are still a hot topic.  Since the extinction events end many evolutionary
>lineages,
>and provide what I would call "empty ecosystem niches" which require
>evolutionary adaptation and change to occupy -- hence mark the beginning or
>major branch point in other evolutionary lineages, I believe the
>mechanism of extinction events is important to discussion of origins.
>And these origins can be either paleontological (what happened here on
>Earth) or astronomical (what was happening in the Solar System.)

	I didn't follow whatever criticism you took, but I substancially
concur with your assessment of the situation. Many of the pivotal twists
in the history of life on earth are due to events external to biology,
itself, and where evolution is a process that picks up the pieces, as it
were, after some rare extreme circumstances. That these events have some
peridocity is another matter, but the point is that there are long times
of stasis (boredom) interspersed with a few moments of terror ( rapid
change under stress). The analogies of stable population dynamics with
self-correcting features is not the whole story. That is the message from
Ralp and Gould, I think, in their idea of Punctuated Equillibria.

>	No influence of a deity, real or implied, should be inferred.

	Oh, I know.

>	The _Science_ article notes "at least 10 mass extinctions 
>have been recognized in the last 250 million years."  The two largest are
>the K/T event, "probably" linked with an asteroid impact, and the P/Tr
>event, now "probably" linked with flood volcanism.  "probably" is my
>inference.

	OK, probably. I will suspend judgement to hear the evidance
that comes in years from now.

>	Anyway, it seems to me this is a valid t.o.pic.  HA!  Perhaps
>the "Flood" wasn't water, it was lava -- of course, a wooden ship
>might have had a problem ;-)

	I see now, you have filled in the flesh on the bones.

	Now, the problems for the unattained. People, here, having
refused to accept the inferences of geology will not get very much
from your first post. It wouldn't really phase some of the Catastrophists
who post here, and hence my question. A second observation is that
replacing the water with basalt in the Biblical flood may stretch
ideas abit, allowing for periodic clensings with flood basalts, but
replacing one universal flood with thousands of little ones to
explain sedimentary strata led to a rupture of the older idea of
one Biblical Flood. I am not really flaming you for the analogy as
I think you use it in jest.


Bruce Salem

Newsgroups: talk.origins