Earth loses its magnetism
By Molly Bentley (december 2003, San Francisco) |
Scientists have known for some time that the Earth's
magnetic field is fading.
Like a Kryptonite-challenged Superman, its strength
has steadily and mysteriously waned, leaving parts of
the planet vulnerable to increased radiation from space.
Some satellites already feel the effects.
What is uncertain is whether the weakened field is on
the way to a complete collapse and a reversal that would
flip the North and South Poles.
Compasses pointing North would then point South.
It is not a matter of whether it will happen, but when,
said scientists who presented the latest research on
the subject at a recent meeting of the American Geophysical
Union in San Francisco.
But when is hard to pinpoint. The dipole reversal pattern
is erratic.
"We can have periods without reversals for many
millions of years, and we can have four or five reversals
within one million years," said Yves
Gallet, from Institut de Physique du Globe de
Paris, France, who studies the palaeomagnetic record
and estimates that the current decay started 2,000 years
ago.
Fluctuations and movement of field strength
across the globe are recorded. |
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Flip or flop |
Over the last century and a half, since monitoring
began, scientists have measured a 10% decline in the
dipole. At the current rate of decline it would take
1,500 to 2,000 years to disappear.
A particular weakness in the field has been observed
off the coast of Brazil in the so-called Southern Atlantic
Anomaly. Here, eccentricities in the Earth's core have
caused a "dip" in the field, leaving it 30%
weaker than elsewhere.
The extra dose of radiation creates electronic glitches
in satellites and spacecraft that fly through it. Even
the Hubble telescope has been affected.
Magnetic reversals were always preceded by weakened
magnetic fields, said Dr Gallet,
but not all weakened fields bring on a flip-flop.
The Earth's invisible shield could also grow back in
strength. "Then sometime, maybe 10,000 years from
now, the dipole will decay again and that will lead
to a reversal," said Harvard physicist Jeremy
Bloxham.
The theme was recently taken up by Hollywood in the
movie The Core, in which the
Earth's core mysteriously stops spinning, effectively
turning off the electromagnetic field. The movie is
nonsense, scientists told BBC News Online, except that
the Earth's magnetic field is generated by activity
deep inside it.
Scientists have detected a fading of the magnetic
field of the earth. |
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Patrick Geryl © 2005 ~ 2008 / site by kAOz :: happyland |
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