Date: Sun, 24 Mar 2002 07:29:19 -0500
To: WSFA members <WSFAlist at keithlynch.net>
From: Candy Madigan <candymadigan at mindspring.com>
Subject: [WSFA] Re: the earth's tilt
Reply-To: WSFA members <WSFAlist at keithlynch.net>

OK, which of you writers is going to write this 'end of the world' story?

It sounds like you've almost got the 'science' worked out.

At 12:39 AM 03/24/2002 -0500, you wrote:

>On Sat, 23 Mar 2002 11:08:46 -0500 Steve Smith <sgs at aginc.net> writes:
>
> > I seem to remember a report that the north *magnetic* pole was
> > moving around more than expected.
>
>The magnetic poles normally wander around within a confined area, in a
>quasi-predictable manner, over time spans of a few years.  Predictable to
>the extent that maps are published showing the isoclines of magnetic
>declination for a given year, accompanied by a table of corrections
>running several years out.  Presumably the south magnetic pole wanders as
>much as the north magnetic pole, but the wanderings of the north magnetic
>pole are of greater interest to people using magnetic compasses in North
>America.
>
>The physical pole would be a lot harder
> > to move -- the Earth is a muckin' big gyroscope.
>
>Angular momentum should be conserved.  It requires external forces to
>change the direction of the earth's axis.  Such forces do act, and over
>time the axis does change direction, slowly.  The axis processes due to
>the Sun's gravity and the earth's equatorial bulge, completing one cycle
>in about 25,000 years.  That is sometimes called 'the precession of the
>equinox'.  Also, there is a slow oscillation in the obliquity of the
>ecliptic, caused (I think) mainly by Jupiter's gravity.
>
>Theories of how the
> > Earth generates its magnetic field are, uhh, incomplete.
> >
>
>The field might be caused by convection in the mantle.
>
> > One of the (kook) theories of why the Earth's crust "tips over"
> > every now and again depends on the reversals in the Earth's magnetic
> > field.  Basically, at the crust-mantle discontinuity, there is a
>magnetic
> > effect that holds the crust onto the rest of the planet.  When the
> > magnetic field goes away during a reversal, the crust isn't held on any
>more
> > and it slides around.  I believe the "Pole Shift" book that somebody
> > mentioned discusses this.
> >
>
>Of course the crust does move around slowly in pieces (continental drift,
>plate tectonics).  The land that we now call Antarctica once had jungles,
>and thus was presumably at much lower latitudes than it is now.  And it
>is generally accepted that magnetic pole reversals occur almost
>regularly.  But that (kook) theory has the whole crust as a unit swapping
>north for south.  As it is, the crust already floats on the mantle.
>Perhaps the theory presumes that the crust is magnetized, so when a
>magnetic pole reversal occurs, it drags the crust on around with the
>field.  Of course the ferromagnetic minerals in the crust are magnetized,
>so the crust is lightly magnetized, but the fly in the ointment is that
>the feeble magnetic forces would not actually be able to move the crust
>much, given the viscosity of the mantle, just as an ant pushing on a
>battleship can't move the ship much, given the viscosity of the water in
>which the ship floats.