Anomalies hint at
magnetic pole flip
19:00 10 April 02
The Earth's magnetic poles
might be starting to flip say researchers who have seen strange anomalies
in our planet's magnetic field.
The magnetic field is created
by the flow of molten iron inside the Earth's core. These circulation
patterns are affected by the planet's rotation, so the field normally
aligns with the Earth's axis - forming the north and south poles.
But the way minerals are
aligned in ancient rock shows that the planet's magnetic dipole
occasionally disappears altogether, leaving a much more complicated field
with many poles all over the planet. When the dipole comes back into
force, the north and south poles can swap places.
The last reversal happened
about 780,000 years ago, over a period of several thousand years. Now
Gauthier Hulot from the Institute of Earth Sciences in Paris and his
colleagues think they have spotted early signs of another reversal.
They used data from the ěrsted
satellite to study strange variations in the Earth's magnetic field. In
particular, one large patch under South Africa is pointing in the opposite
direction from the rest of the Earth's field and has been growing for
hundreds of years.
The anomalies have already reduced the overall
strength of the planet's magnetic field by about 10 per cent. If they
continue to grow at the same rate, the Earth's dipole will disappear
within just two millennia.
But ěrsted is the first satellite to take a
snapshot of the Earth's magnetic field for 20 years, and such scant data
makes it difficult to predict future shifts.
"We can't really tell what will
happen," says Hulot. "But we speculate that we're in an unusual
situation that might be related to a reversal."
Journal reference: Nature
(vol 416, p 620)
The Earth's magnetic field is showing
worrying signs that it is about to reverse again. The magnetic north pole
has wandered by 1100 kilometres in the past 200 years and its (magnetic
field) strength is dropping at a rate of 5 per cent a century.
This is the fastest decrease since the last
reversal 730,000 years ago.