From: jgacker@news.gsfc.nasa.gov (James G. Acker)
Subject: Re: Permo/Triassic quandary
Organization: NASA Goddard Space Flight Center - Greenbelt, MD USA
X-Newsreader: TIN [version 1.1 PL6]
Date: Wed, 6 Jan 1993 21:29:32 GMT

Bruce Salem (salem@pangea.Stanford.EDU) wrote:
: 	I am not clear about how Jim's discussion of asteriod
: impacts in the history of the sieberian traps, or in other
: possibly pivotal plate tectonic events, relates to the rest
: of the discussion in talk.origins . I am not suggesting

Since what you said should be seen twice, I'm just noting here
that I'll answer your question below.


: that Jim embraces the type of Catastrophism being otherwise
: debated, nor am I questioning the geologic sense of what
: he is writing about. It would seem to me that as we don't
: really know what the driving mechanism for plate tectonics,
: the mantle is convecting and that seems to drive crustal
: turnover but we do not know why, that asteroid impacts
: are a uniform part of the history of the earth and that
: they have catastrophic effects, but their rare inevatibility
: is strictly Uniformatarian in process. If anyone is suggesting
: that asteriods have a literal big impact on plate tectonics
: that I would like to hear more discussion of how.
: 
: Bruce Salem
: 

	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.

	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.)

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

	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.

	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 ;-)


	
============================================================
|  James G. Acker                       Occasional Genius  |
|  jgacker@neptune.gsfc.nasa.gov        Regular Swimmer    |
|                                                          |
|  "Animal-based research in this field ignores the fact   |
|  that in humans much sexual behavior has little to do    |
|  with reproduction both psychologically and physio-      |
|  logically..."                                           |
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Newsgroups: talk.origins