~e; shifty EM geopoles?
Sun, 21 Apr 2002 15:43:54 -0500
[registration is needed for this article from the UK's Daily
Telegraph. thus, it is being sent as is, as a partial quote
may degrade the complexity of the work, and its non-commercial
educational understanding. in any case, i was wrong, must have
read previously that the geomagnetic poles moved around every
once and awhile, but did not 'flip' as this states, as it is
of another scale of things. also, note the idea of a geodynamo
based on the earth's EM fields. link this up with the northern/
southern lights, and there is universal-class EM audiovisual show.
thanks to * for sending info i misplaced about finding this online.
to read more and all of the links, please register. two urls are
provided at the end, part of a list that is at the original URL.]
How our world could be turned upside down
Sunday 21 April 2002 (Filed: 17/04/2002)
The north and south poles may be about to swap places, with worrying
implications for life. David Derbyshire reports
HOMO ERECTUS, our tool-making ancestor, never got around to inventing the
compass. But if she had, she would have noticed something odd happening to the
Earth's poles 780,000 years ago.
Slowly but surely, the world was turning on its head. The north magnetic pole,
for our tool-making African ancestors, was bang in the middle of Antarctica A
modern compass would have shown the northernmost point of the continent as the
Cape of Good Hope while far to the south lay the Mediterranean and Europe.
But over the centuries the poles began to move. A compass needle on the
prehistoric Earth would have begun to swing erratically from point to point
until, after a few thousand years, it settled on a new direction. The new North
Pole was now at the bottom of the ancient world, in the centre of the ice cap we
call the Arctic.
The flip-flopping of poles every few hundreds of thousands of years is one of
the more mysterious rhythms of the planet. During the changeover, which lasts up
to 5,000 years, the magnetic field is weakened, reducing its protection against
harmful solar winds.
Since the last great flip in the time of Homo erectus, the poles have been
relatively stable. But there are now rumblings that a change could be under way.
Last week, French and Danish scientists announced that they had spotted a
peculiar anomaly in the magnetic field whose origins lay in the spiralling
columns of liquid metal that flow in the core of the planet. These vortices
could be the engines that drive the pole-flipping process.
The origin of the Earth's magnetic field was described by Einstein as one of the
three great unsolved puzzles of physics. Lines of magnetic force flow from the
South Pole, loop up around the Earth and end up in the North Pole, creating a
At one time it was thought that there was the equivalent of a giant iron bar
magnet running through the Earth. However, temperatures at the planet's core are
simply too hot for a conventional magnet. And the magnetic field is as old as
the most ancient rocks on Earth. Any magnet should have dissipated tens of
thousands years after the creation of the Earth.
The solution proposed 50 years ago was the geodynamo. The core of the Earth - a
ball of molten iron and nickel with a solid nugget at its centre - is still
cooling down from the creation of the Earth. Hot material is spiralling in
vortices from the inside of the outer core to its boundary at speeds of about
six miles a year, a movement shaped by the Earth's rotation.
The movement of any conductor within a magnet, such as the Earth's magnetic
field, generates electricity: it's the principle of a dynamo. But the size of
the core means that the currents generated are colossal. These currents have
massive magnetic forces that renew and re-energise the pre-existing magnetic
The geo-dynamo is a little like the chicken and the egg. You need the magnetic
field to create the electrical current but you need the current to re-energise
the magnet. Originally, there must have been a seed magnet that started the
whole process off, possibly supplied by the Sun.
By studying the magnetic field on the surface, it is possible to see what is
happening at the top of the core, roughly 1,800 miles below. Dr Gauthier Hulot
of the Institut de Physique du Globe de Paris and colleagues at the Danish Space
Research Institute in Copenhagen used magnetic field measurements taken by the
Danish Oersted satellites and compared them with similar readings made in 1980
by the American Magsat satellite.
The results, published in Nature, confirmed that the Earth's magnetic field is
getting weaker. If it continues to weaken at its current rate, the dipole field
will have vanished in 2,000 years. But Dr Hulot and his team also found a large
area of "reversed magnetic flux" - where the magnetic field runs counter to the
rest of the world's field - below South Africa and the Southern Ocean. Normally,
lines of field move from the south to the north. But in this "reversed flux"
area, the magnetic field lines loop backwards and head south. Under this area,
the columns of moving liquid iron in the core may be rotating a little
differently than they are in the rest of the core, locally weakening and
reversing the magnetic field.
The team also found an area where the field is stronger on the opposite side of
the world, under the Pacific. This asymmetry could be part of the chaotic
mechanism that periodically reverses the poles.
"This patch of reverse flux under South Africa is growing and the strength of
the field over all the world has been decreasing. If this is going to continue,
will this lead to a reversal? It is a difficult one to answer," says Dr Hulot.
If the Earth's core were to freeze tomorrow, it would take up to 40,000 years
for the magnetic field to ebb away. And yet the reversals take place over just a
few thousand years.
"We need an active process for it to happen so quickly and this is an active
process that we see now. We suspect that a similar process could lead to a
reversal," says Dr Hulot.
The area of reverse flux was predicted in the first successful simulations of
the magnetic field, created by Dr Gary Glatzmaier of the University of
California, Santa Cruz, and Dr Paul Roberts of UC, Los Angeles, in the mid
"These are exciting results," says Dr Glatzmaier. "They show vortices, which
have also been seen in some computer simulations of the geo-dynamo. They also
see how the reversed magnetic flux patches have been growing and suggest that
this could be a precursor for the next magnetic dipole reversal.
"The spontaneous dipole reversals that have been seen in computer simulations of
the geo-dynamo have all been unique in terms of where the magnetic instability
begins and how long the reversal takes; however, they typically begin as a
growth of reversed magnetic flux patches and a decrease in the dipole intensity,
not unlike what we are seeing in today's geomagnetic field."
So is this the first sign of a reversal? One argument in favour is that a flip
is long overdue. The last took place 780,000 years ago. Over the past few
million years they have tended to arrive every 250,000 years on average. But
there are longer gaps. Between 118 million and 83 million years ago there were
The weakening of the magnetic field has also been used as evidence of a coming
flip. Dr Hulot is not convinced that the other signs are clear. "Although the
strength is decreasing fast, its absolute value is still high by geological
standards. It has been quite high in the recent past. Its maximum was about
2,000 years ago. Usually before reversal there is a strong trend where the
magnetic field decreases over tens of thousands of years. We have not seen such
a decrease in the past 50,000 years."
If a flip is due, should we be worried? The magnetic field protects against
charged particles of the solar wind. Once the flip is under way, the overall
magnetic field drops to a tenth of its pervious strength, while several poles
appear all over the Earth. The field eventually returns to its full strength
with the poles reversed.
"To my knowledge," says Dr Hulot, "there has not been any evidence of
extinctions of species in past reversals. But the reversing dipole structure
would change the interaction of the Earth with the solar wind." One side effect
could be an increase in cancers as more charged particles flow to the Earth "I
believe this would influence life significantly for a certain of amount of time
and might shorten life span of animals. But it would not kill species," says Dr
Core Convection and the Geodynamo - Los Alamos National Laboratory
Geodynamo - US Geological Survey
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