Occidental Professor Tracks Rapid Movement in Ancient Geomagnetic Field Change
Occidental College geology professor Scott Bogue has recently found evidence of a brief episode of rapid geomagnetic field change that was thousands of times faster than usual.
The findings may throw into question scientific knowledge about Earth's geomagnetic field reversals, when the magnetic north pole flips to the south pole, and vice versa.
Geomagnetic field reversals happen every few hundred thousand years and take several thousand years to complete. Bogue and his research colleague, Jonathan Glen of the U.S. Geological Survey in Menlo Park, Calif., studied 15 million year-old lava flows in a Nevada mountain range, Sheep Creek Range. In particular, they used Occidental's super-conducting rock magnetometer to analyze the magnetization of a 13-foot thick lava flow that had erupted as the geomagnetic field was reversing polarity.
They discovered that the lava flow contains two magnetic patterns acquired within about a year of each other as the lava cooled. The patterns differ in direction by 53 degrees, implying that the geomagnetic field was changing at a rate of about one degree per week. The team will publish their findings in an upcoming issue of Geophysical Research Letters.
"This rapid field movement happened toward the end of a several-thousand year long reversal," Bogue said. "Other evidence suggests that the polarity reversal is a very unsteady process, with periods of standstill as well as rapid change."
Serendipity played a role in the geologists' research. Bogue was initially interested in rocks in Argenta Rim, just southeast of Sheep Creek Range. Those rocks turned out to be a dead end. But instead of packing up his equipment and going home, Bogue decided to look at Sheep Creek Range since it was close. And that's where he and Glen eventually struck paleomagnetic gold.
"The preliminary results were very intriguing, and we got a sense that it was worthwhile to do a more detailed study," Bogue said.
Their research, funded by National Science Foundation grants, also brings more credence to a similar instance - the only other example discovered so far - found at Oregon's Steens Mountain in 1995. The researchers for the earlier study analyzed lava flows 1.2 million years older than the rock at Sheep Creek Range and found evidence of an episode of a 6-degree per day change. That rate of directional change was so high that many in the earth science found it hard to accept.
Humans cannot directly sense geomagnetic field reversal. Even an episode of rapid field change would be extremely hard to detect unless one used a compass at the exact location of rapid change at exactly the right time. As for a polarity reversal's effect on global-positioning devices, such instruments rely on satellites rather than the magnetic field, so there is no direct connection, Bogue said.
Scientists don't know why the Earth's magnetic fields flip, Bogue added. Geomagnetic field polarity reversals somehow arise from the turbulent fluidity in the Earth's super-hot core, but nobody really knows the details. Like Earth, stars and many planets have magnetic fields. In the case of the Sun, the magnetic field reverses polarity every 11 years.
Earth's magnetic field helps protect our planet from the solar wind. It also serves as a navigational tool for organisms such as pigeons, bees and even bacteria.
Geophysical Research Letters can be found at http://www.agu.org/journals/gl/index.shtml