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Fast decline of magnetic field hints at reversal

The collapse of the Earth's magnetic field, which both guards the planet and guides many of its creatures, appears to have started in earnest about 150 years ago. The field's strength has waned 10 to 15 percent so far, and this deterioration has accelerated of late, increasing debate over whether it portends a reversal of the lines of magnetic force that normally envelop the Earth.

During a reversal, the main field weakens, almost vanishes, and then reappears with opposite polarity. Afterward, compass needles that normally point north would point south, and during the thousands of years of transition much in the heavens and Earth would go askew.

A reversal could knock out power grids, injure astronauts and satellites, widen atmospheric ozone holes, send polar auroras flashing to the equator and confuse birds, fish and migratory animals that rely on the steadiness of the magnetic field as a navigation aid. But experts said the repercussions would fall short of catastrophic, despite a few proclamations of doom and sketchy evidence of past links between field reversals and species extinctions.

Damage to satellites

Although a total flip may be hundreds or thousands of years away, the rapid decline in magnetic strength is already damaging satellites.

Last month, the European Space Agency approved the world's largest effort at tracking the field's shifts. A trio of new satellites, called Swarm, are to monitor the collapsing field with far greater precision than before and help scientists forecast its prospective state.

``We want to get some idea of how this would evolve in the near future, just like people trying to predict the weather,'' said Gauthier Hulot, a French geophysicist working on the satellite plan. ``I'm personally quite convinced we should be able to work out the first predictions by the end of the mission.''

The discipline is one of a number -- like high-energy physics and aspects of space science -- where Europeans have recently come from behind to seize the initiative, dismaying some U.S. experts.

2,000 years to mature

No matter what the new findings, the public has no reason to panic, scientists say. Even if a flip is imminent, it might take 2,000 years to mature. The last one took place 780,000 years ago, when Homo erectus was still learning how to make stone tools.

Some experts suggest a reversal is overdue. ``The fact that it's dropping so rapidly gives you pause,'' said John Tarduno, a professor of geophysics at the University of Rochester. ``It looks like things we see in computer models of a reversal.''

In an interview, Tarduno put the odds of an impending flip at more likely than not, adding that some of his colleagues were placing informal bets on the possibility but realized they would probably be long gone by the time the picture clarified.

Deep inside the Earth, the magnetic field arises as the fluid core oozes with hot currents of molten iron and this mechanical energy gets converted into electromagnetism. It is known as the geodynamo. In a car's generator, the same principle turns mechanical energy into electricity.

No one knows precisely why the field periodically reverses but scientists say the responsibility probably lies with changes in the turbulent flows of molten iron, which they envision as similar to the churning gases that make up the clouds of Jupiter.

In theory, a reversal could have major effects, because over the ages many aspects of nature and society have come to rely on the field's steadiness.

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