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 ~ 2007 / site by kAOz :: happyland |
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