Robin McKie, science editor Monday July 04, 2005 The
Earth's magnetic field - the
force that protects us from deadly radiation bursts from outer space - is
Scientists have discovered that its strength has
dropped precipitously over the past two centuries and could disappear over the
next 1,000 years.
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
'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
'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.'
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.
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.
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
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
And as Scientific American reports this week, this interpretation
has now been backed up by computer simulation studies.
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.
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.
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.
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.
'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.'
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.
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.
Given that temperatures at such depths
rival those of the Sun's surface, such a task would seem impossible - except, of
course, in Hollywood.