SOME 16 million years ago, north became south in a matter of years. Such fast flips are impossible, according to models of the Earth鈥檚 core, but this is now the second time that evidence has been found.
The magnetic poles swap every 300,000 years, a process that normally takes up to 5000 years. In 1995 an ancient lava flow with an unusual magnetic pattern was discovered in Oregon. It suggested that the field at the time was moving by 6 degrees a day 鈥� at least 10,000 times faster than usual. 鈥淣ot many people believed it,鈥� says of Occidental College in Los Angeles.
Now Bogue and his colleague of the United States Geological Survey in Menlo Park, California, say they have found a second example in Nevada. The lava rock suggests that in one year, Earth鈥檚 magnetic field shifted by 53 degrees (). At that rate, a full flip would take less than four years, but there could be another interpretation. 鈥淚t may have been a burst of rapid acceleration that punctuated the steady movement of the field,鈥� says Bogue.
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of Johns Hopkins University in Baltimore, Maryland, remains sceptical and points out that the effects could have been local rather than global.
Earth is overdue for a reversal, and rapid shifts would cause widespread chaos 鈥� for navigation and migratory birds for instance.
