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From: karish@denali.UUCP (karish)
Newsgroups: sci.bio,sci.misc,rec.birds
Subject: Re: animals and Earth's magnetic reversal
Message-ID: <20@denali.UUCP>
Date: 16 Mar 88 05:51:03 GMT
References: <7387@ihlpa.ATT.COM> <460@amethyst.UUCP>
Reply-To: crkarish@stanford.edu (Chuck Karish)
Organization: Mindcraft, Inc.
Lines: 20

In article <460@amethyst.UUCP> hdunne@amethyst.ma.arizona.edu (|-|ugh) writes:
>In article <7387@ihlpa.ATT.COM> cutler@ihlpa.ATT.COM (Herber) writes:
>
>}  Will Northern hemisphere birds migrate north
>}in the winter?  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