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Interesting you should mention this topic. The last theory that I read was
that the magnetic goes in cycles; that is, it reaches a peak strength in one
polarity and then gradually decreases to almost zero, after which it starts
to increase in strength although not necessarily in the same polarity.

According to Dutton (14th edition, Maloney):
------------------
"...it is known that there have been 12 reversals of magnetic polarity over
the past nine million years and that we are overdue for another. The earth's
field intensity has decreased over 50 percent in the last 4,000 years, and
one study predicts that in 1,200 years or so magnetic compasses will become
useless -- there will be no field to direct them and they will point in any
direction. Although all decreases do not result in reversal, when the field
returns a few centuries later, its polarity is more likely than not to have
reversed!"
------------------

I have further read that mass extinctions may have occured during these
period of magnetic "calm". This is because the magnetic field provides some
protection from incoming cosmic rays and other extra-terrestrial nasties.
Without the field, we get a good saturation from all directions.

Another theory that I read -- and this is based on a book that was written
on the topic --  that the reversals happen suddenly. According to the author
(whose name escapes me) the collapsing magnetic field induces a huge
electric "shock" that rips through the oceans, killing everything in its
path. I should point out that the author of this book had zero scientific
credentials and admitted as much. In fact he felt that because he was
unencumbered by scientific dogma, he was more qualified to offer a fresh
theory!

Whatever theory one chooses to believe, I find it a depressing thought that
my old reliable compass will some day be as useless as a GPS without
batteries. Although I won't be around to ponder the problem.

cheers,

Robert



----- Original Message -----
From: Jared Sherman 
To: 
Sent: Monday, February 10, 2003 12:14 AM
Subject: Re: GPS & Magnetic Bearings


> Robert-
>  Sounds spot on. I understand there is even still some debate on how fast
the poles reverse, and whether that might take us all unawares one day. (Not
literally in one day.)
>

   

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