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10/24/2002
Are We Flipping?
I''ve often said that we should devote more resources to the
detection of objects in outer space that could impact our planet
and lead to our extinction. Such a self-centered effort might help
us to take measures to avoid the fate of the dinosaurs, done in by
such an object 60 million years ago. I hadn''t even considered the
possibility that another star might collide with our sun. The
November Scientific American features an article that, thank
goodness, gives assurance that we won''t have to worry about a
white dwarf star hitting our sun any time soon. So, I won''t take
up your time with the details of such a catastrophe. The sight of
the sun taking on the shape of a pear as the dwarf approaches,
pictured on the cover of the magazine, is scary enough!
However, another article in that issue treats a more immediate
life-altering global event that may be in progress even as we
speak. The one-page article is "Headed South?" by Sarah
Simpson. What''s headed south? The North Pole! To be more
precise, it''s the magnetic North Pole (MNP). Perversely, you
point out to me that, at the moment, the MNP is actually moving
north, not south, in an elliptical pattern out of Canada into the
Arctic Ocean. Your concerns led me to resolve this apparent
discrepancy by visiting the Web sites of such eminent sources as
USA Today, the National Post in Canada and the Guardian in the
UK. I also logged onto NASA''s Web site for more authoritative
information.
In spite of the MNP''s current movement north, we may be on our
way to a reversal of the earth''s magnetic field - a magnetic flip.
A magnetic flip would cause our compass to point south instead
of north. Will we in New Jersey be saying that we''re going north
to Florida for the winter? But I shouldn''t be flippant about a flip.
Earth''s magnetic field is more important to us than its role in
guiding mariners or souls lost in the woods. It, along with the
ozone layer, helps shield us from a goodly portion of the harmful
radiation and particles ejected from our sun and from cosmic
rays from outer space. The magnetic field guides charged
particles to our sparsely inhabited Polar Regions and the
resulting auroras enthrall, not bedevil us.
The source of Earth''s magnetic field has been a mystery; even
Einstein called it one of the great mysteries of science. Today,
the prevailing view involves the sloshing around of a gigantic
pool of liquid, mostly iron, surrounding a solid core at the center
of the earth. This sloshing around of the iron generates electrical
currents that in turn generate magnetic fields, akin to how you
can make a magnet by passing a current through a coil of wire.
I''m assuming that the earth spinning on its axis will influence the
sloshing and will tend to make the flow somewhat more orderly
than the term "sloshing" implies. However, we shouldn''t be
surprised if there are regions in the sloshing iron where the
resulting magnetic field points north, others where it points south
or some other direction. If more point north, then we have the
situation of today - north is north. But suppose that, over a
period of time, the balance shifts to more and more regions
pointing south. Eventually, south wins out, the magnetic poles
flip and our compass points south.
Why do the experts think another flip is on the way? Well, for
the past 40,000 years or so, the strength of the earth''s magnetic
field has been falling until it''s about 50 percent weaker than it
was way back then. However, in the last century or so, it has
dropped roughly 5 percent, a very substantial drop in such a short
time. A drop is to be expected if the south-pointing magnetic
regions are becoming more and more numerous. Recent satellite
data gathered by Gauthier Hulot of France and his colleagues
show patches near the North Pole and down below the tip of
Africa where the magnetic field lines point toward the center of
the earth. The prevailing lines in those areas point to the surface.
Hulot and co-workers contend that these patches are caused by
eddies in the overall flow in the molten iron. Model computer
simulations predict that eddies can result in magnetic flipping.
Is a magnetic flip a rare occurrence? Not at all. There have been
hundreds of flips over the past half billion years. The last one
was 740 thousand years ago, according to NASA. The times
between flips have ranged all the way from 5,000 to 50 million
years. The time to flip once the process begins may take only
one to a few thousand years, although the whole process may
take half a million years. You can see that flipping is not very
predictable.
A magnetic flip on another member of our solar system occurred
in February of 2001. In 2012, it will flip again. Sun lovers will
recognize that 11-year interval as the duration of the sunspot
cycle. A magnetic flip occurs on the sun quite predictably on the
same cycle. Last year marked the solar maximum, with sunspot
activity at its peak. Sunspots are associated with areas on the sun
sporting huge magnetic loops much stronger than the sun''s
magnetic field, which is about as strong as a kitchen magnet.
(Earth''s is a hundred times weaker.)
The sun''s magnetic field also serves us by shielding the whole
solar system from some of the cosmic rays. This field gets
transported to the edges of our solar system by the solar wind,
forming the bubble we talked about a couple months ago in
connection with the Voyagers. The variation in the intensities of
cosmic rays (which varies with the sunspot cycle) and the
ejection of particles from the sun may influence our weather and
certainly can influence our satellite communications. Astronauts
have to pay particular attention out in space.
With Earth''s magnetic field weakening and perhaps going to zero
before reversal, it seems that all sorts of problems could arise.
For example, more radiation hitting the earth could increase the
risk of skin cancer. Birds and bees rely in varying degrees on the
earth''s magnetic field for guiding them on flights ranging from
thousands of miles to hundreds of yards. Will they evolve to
take into account the weakening and reversal of the magnetic
field? Will our species be doomed? Take heart. In the hundreds
of reversals to date there is no evidence of any noteworthy
extinctions. And we probably don''t have to face the flip for
another thousand years or so. Sleep well tonight.
I''ve discussed predictability, or lack of it, for magnetic flips on
two different bodies, our sun and the earth. In passing, I
mentioned the dinosaurs, who couldn''t have predicted their
sudden demise. I''m trying desperately to segue gracefully into
an October 11 item on the National Geographic Web site that I
can''t resist calling to your attention. Could Leonard Webb and
Geneva Jordan, who inscribed their names on a rock in Montana
back in 1917, have predicted that 85 years later Leonard would
have one of the most important dinosaur finds in history named
after him?
Poor Leonardo, a duck-billed dinosaur, died 77 million years ago
at the tender age of three or four years. His fossil was excavated
last year in a single six and a half-ton block of rock. Leonardo
was found near the rock bearing the 1917 Leonard-Geneva
graffiti; hence the name Leonardo. What''s so special about
Leonardo? He''s reportedly the biggest dinosaur ever taken out of
the ground in one chunk. But that''s minor compared to the fact
that Leonardo is only the fourth dinosaur fossil ever to be
classified as a "mummy". His complete skeleton is 90 percent
covered in soft tissue and even his last meal was preserved so
well in his stomach that it could be identified - a "salad of ferns,
conifers and magnolias." The other three dinosaur "mummies"
were found early in the last century and today''s sophisticated
preservation techniques were not available. I think I can safely
predict that some future Geographic issue will feature Leonardo
and the scientific studies bound to follow on such a rare fossil. I
can''t wait.
Finally, I should hasten to add that my explanation of the origin
of the earth''s magnetism is quite simplistic. There are other
sources of magnetism that will probably prevent the strength of
Earth''s field from going to zero before the flip. And nobody can
predict when the flip will happen. Again, I''m not going to lose
any sleep over it.
Allen F. Bortrum
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