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From: bpdickson@trillium.waterloo.edu (Brian P. Dickson)
Newsgroups: sci.bio,sci.misc,rec.birds
Subject: Re: animals and Earth's magnetic reversal
Message-ID: <5792@watdragon.waterloo.edu>
Date: 17 Mar 88 20:34:41 GMT
References: <7387@ihlpa.ATT.COM> <460@amethyst.UUCP> <20@denali.UUCP>
Sender: daemon@watdragon.waterloo.edu
Reply-To: bpdickson@trillium.waterloo.edu (Brian P. Dickson)
Organization: U. of Waterloo, Ontario
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In article <20@denali.UUCP> crkarish@stanford.edu (Chuck Karish) writes:
>In article <460@amethyst.UUCP> hdunne@amethyst.ma.arizona.edu (|-|ugh) writes:
>>}Are there any indications of specie disappearance during
>>}these times?
>>
>>Geomagnetic reversals take place at random intervals on the order of several
>>million years. Each individual reversal takes about ten thousand years for the
>>process to be completed.
>>
>
>During polarity reversals, which probably take ten thousand years or more,
                                  ^^^^^^^^
>the earth's magnetic field is probably weak and irregular, and generally
                               ^^^^^^^^                         ^^^^^^^^^
>useless for navigating.  The dates of ancient extinctions are not known
>precisely enough to allow convincing correlations with magnetic reversals;
                           ^^^^^^^^^^
>for that matter, the timing of reversals longer ago than ten million years
>is not known too precisely, either.
>
>Chuck

***FLAME ON: AAAAAARGHH!! The 'net is supposed to be used for the dissemination
of useful information, not freshmen's humble opinions. Not only is your posting
conjecture, but it is most probably *wrong*!
***FLAME OFF

In a recent issue of {Popular Science | Scientific American | Nat'l Geographic},
some scientists from several disciplines had worked together to produce a very
convincing arguement for their theory. It links several *very* *important*
elements of observed information in different areas, and could possibly give
us a better understanding of several areas in science.

Theorem in brief: Every 30 million years or so, another star (our sun's evil
twin brother, as it were) passes very close, by cosmic distances, to our sun,
close enough to disturb the Van Oort comet cloud. For the next while, a lot
of comets make close passes to our sun in highly elliptical orbits. Every now
and then, on the average of every 10000 years, a larger-sized comet strikes
the earth's atmosphere. If it is big enough, the equivalent of a nuclear winter
occurs: debris scattered into the upper atmosphere, for long enough that the
earth's albedo increases significantly, and an ice age occurs. As more water
freezes, the earth's rate of rotation increases. This in turn screws up the
core of the planet in such a way that the magnetic field (which is weak to 
start with) reverses. When the air clears, the ice melts, the earth slows,
and the field reverses again. For *very* big comets, it gets *real* cold,
and mass extinctions occur.

These scientists were geophysicists, paleontologists, and astronomers, and
they plotted known data: extinctions, ice ages, magnetic reversals, increases
in rare-earth metals (which are common in comets) being deposited, and so on.
The coincidences are all over the time line, far too close and far too often
to be taken lightly. Incidentally, the evil-twin sun could account for our
planets being formed as well; the 30 million year period with high eccentricity
makes finding the bugger very difficult.

--
Brian Dickson,
closet scientist