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Earth's Poles Begin Magnetic Reversal
Posted: April 18, 2002
Courtesy: The National Post

Researchers in the British science journal Nature say the Earth is beginning a magnetic reversal. Satellite imagery suggests that compasses will point south within a few thousand years, a mere heartbeat in geological time. This is because the complex flow of molten iron deep within the Earth, which maintains the planet's polarity, is reversing.
Deep below the Earth's crust around the southern tip of Africa, Danish and French scientists noticed strange changes in the flow of the planet's liquid outer core.

They had been studying maps of the Earth's magnetic field, which they drew with data from two satellites: the U.S. Magsat, which flew in the 1970s, and the Danish Oersted, which remains in orbit. The satellites' sensitive magnetic readers are useful to geophysicists since the magnetic field above the Earth's surface mirrors the flow of liquid iron below.

By comparing how the readings changed, the researchers noticed reversals in certain vertical features of the flow. The general westward rotation was still in place, but iron that was supposed to be flowing down toward the centre was flowing up, and vice versa.

These "magnetic flux reversals" are characteristic of the beginning of a total reversal of the planet's poles, according to the researchers, who report their findings in today's edition of Nature, the British science journal. Such reversals happen about once every million years.

Compasses, which point to magnetic north, will retain their usefulness for quite some time, though. Magnetic polarity reversal is among the fastest geological processes, but it still takes a few thousand years, said David Dunlop, a geophysicist at the University of Toronto.

The magnetic north pole is currently near Ellef Ringnes Island in the Canadian Arctic, moving constantly in an elliptical pattern while drifting steadily north. It will soon leave Canadian territory. The magnetic south pole is off the coast of Antarctica.

As the poles switch, the intensity of the Earth's magnetic field will decrease to around one-tenth its current strength, and it will remain this way for around 3,000 years, Dr. Dunlop said. Then, the complex flow patterns will reinforce each other until they once again form the planetary version of an electric dynamo. As this happens, the magnetic field will gradually power up to full strength -- completely reversed.

Peter Olson, a geophysicist at Johns Hopkins University in Baltimore, who wrote a commentary on the discovery in Nature, said the strength of the Earth's magnetic poles have been getting steadily weaker over the past 150 years. At its current rate, it will vanish early in the next millennium.

The new research explains nearly all of this decrease, he said. Satellite imagery is the only way this could have been explained, he added, since no holes are dug that deep, and monitoring seismic activity sketches only a rough picture.

The history of the Earth's polarity is a long series of minor fluctuations over millions of years, punctuated by total reversals that take place over just a few millennia.

The patterns they leave behind have been used by scientists to study such astoundingly slow processes as continental drift. In one recent study, researchers calculated how fast two tectonic plates were drifting apart by counting the strips of oppositely-polarized rock on the ocean floor, which were formed as molten rock cooled there and was magnetized according to the polarity of the day.

At once every million years, magnetic polarity reversals are much more common now than in the early ages of the Earth, Dr. Dunlop said.