"Geomagnetic field reversals" of the Earth's magnetism occur every couple hundred thousand years and normally take about 4,000 years but the Nevada finding suggest at least one particular reversal of the globe's magnetic poles happened much faster, ScienceNews.org reported.
The discovery bolsters the theory, first proposed after a similar examination of rocks in Oregon in 1995, that reversals really can happen quickly, over the course of years or centuries instead of millennia, researchers say.
"We're trying to make the case that [the new work] is another record of a superfast magnetic change," says lead author Scott Bogue, a geologist at Occidental College in Los Angeles.
Bogue studied a series of well-preserved lava flows. As each flow cooled, it preserved evidence of the magnetic field at the time, locked like tiny compass needles in the magnetic crystals in the lava.
One particular flow showed the crystals reorienting themselves 53 degrees within a single year, the study said.
Researchers aren't sure why the geomagnetic field reverses, though most say it's connected to what creates the field in the first place: convective motions of liquid iron in the planet's spinning outer core.
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