Scientists have long been aware that the Earth's magnetic poles move ever so slightly every decade or so. However, the movement is thought to be so gradual that navigation devices are not affected. Now a team of researchers report that short-lived periods of “astonishingly rapid field change” are possible. In fact, the field can move as much as 6° a day, which would challenge the most sophisticated of navigational tools, the team reports in the April 20 edition of Nature. On the basis of paleomagnetic data from lava flows at Steens Mountain, Oregon, R.S. Coe from the University of California at Santa Cruz and his colleagues at the University of Montpelier in France claim such rotations took place about 16.2 million years ago over an 8-day period. Scientists have long been aware of the Earth's field reversals— when the magnetic north and south poles trade places. Such reversals occur every few hundred thousand years and take thousands of years to be complete. The Steens Mountain data indicate that the rapid shifts occurred during a magnetic reversal. But such shifts are clearly outside conventional geologic wisdom.