- Earth's magnetic field - the force that protects us from
deadly radiation bursts from outer space - is weakening dramatically.
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- Scientists have discovered that its strength has dropped
precipitously over the past two centuries and could disappear over the
next 1,000 years.
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- The effects could be catastrophic. Powerful radiation
bursts, which normally never touch the atmosphere, would heat up its upper
layers, triggering climatic disruption. Navigation and communication satellites,
Earth's eyes and ears, would be destroyed and migrating animals left unable
to navigate.
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- 'Earth's magnetic field has disappeared many times before
- as a prelude to our magnetic poles flipping over, when north becomes
south and vice versa,' said Dr Alan Thomson of the British Geological Survey
in Edinburgh.
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- 'Reversals happen every 250,000 years or so, and as there
has not been one for almost a million years, we are due one soon.'
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- For more than 100 years, scientists have noted the strength
of Earth's magnetic field has been declining, but have disagreed about
interpretations. Some said its drop was a precursor to reversal, others
argued it merely indicated some temporary variation in field strength has
been occurring.
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- But now Gauthier Hulot of the Paris Geophysical Institute
has discovered Earth's magnetic field seems to be disappearing most alarmingly
near the poles, a clear sign that a flip may soon take place.
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- Using satellite measurements of field variations over
the past 20 years, Hulot plotted the currents of molten iron that generate
Earth's magnetism deep underground and spotted huge whorls near the poles.
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- Hulot believes these vortices rotate in a direction that
reinforces a reverse magnetic field, and as they grow and proliferate these
eddies will weaken the dominant field: the first steps toward a new polarity,
he says.
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- And as Scientific American reports this week, this interpretation
has now been backed up by computer simulation studies.
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- How long a reversal might last is a matter of scientific
controversy, however. Records of past events, embedded in iron minerals
in ancient lava beds, show some can last for thousands of years - during
which time the planet will have been exposed to batterings from solar radiation.
On the other hand, other researchers say some flips may have lasted only
a few weeks.
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- Exactly what will happen when Earth's magnetic field
disappears prior to its re-emergence in a reversed orientation is also
difficult to assess. Compasses would point to the wrong pole - a minor
inconvenience. More importantly, low-orbiting satellites would be exposed
to electromagnetic batterings, wrecking them.
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- In addition, many species of migrating animals and birds
- from swallows to wildebeests - rely on innate abilities to track Earth's
magnetic field. Their fates are impossible to gauge.
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- As to humans, our greatest risk would come from intense
solar radiation bursts. Normally these are contained by the planet's magnetic
field in space. However, if it disappears, particle storms will start to
batter the atmosphere.
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- 'These solar particles can have profound effects,' said
Dr Paul Murdin, of the Institute of Astronomy, Cambridge. 'On Mars, when
its magnetic field failed permanently billions of years ago, it led to
its atmosphere being boiled off. On Earth, it will heat up the upper atmosphere
and send ripples round the world with enormous, unpredictable effects on
the climate.'
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- It is unlikely that humans could do much. Burrowing thousands
of miles into solid rock to set things right would stretch the technological
prowess of our descendants to bursting point, though such limitations do
not worry film scriptwriters. Paramount's latest sci-fi thriller, The Core
- directed by Englishman Jon Amiel, and starring Hilary Swank and Aaron
Eckhart - depicts a world beset by just such a polar reversal, with radiation
sweeping the planet.
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- The solution, according to the film, to be released next
year, involves scientists drilling into Earth's mantle to set off a nuclear
blast that will halt the reversal.
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- Given that temperatures at such depths rival those of
the Sun's surface, such a task would seem impossible - except, of course,
in Hollywood.
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- Guardian Unlimited © Guardian Newspapers Limited
2002
- http://www.observer.co.uk/international/story/0,6903,837058,00.html
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