Posted on April 05 2016
Way back in 1906, a French geologist named Bernard Brunhes made a fascinating discovery. He knew that previous studies had shown that baking pottery or bricks caused iron particles in the clay to align in a north-south orientation. Heat of sufficient intensity causes the electrons in iron to go into a high-energy state and become “looser,” facilitating realignment. In studying the clays over which lava had once flowed, he found that iron particles in both the lava and the baked clay underneath it had the same orientation. Then further study in places where there were multiple layers of lava showed that different lava layers had opposite alignments. The only logical explanation was that, amazingly enough, the magnetic poles of the earth must be periodically reversing. This realization made it clear that the earth is not a static system; it’s a system driven by powerful forces not always in balance. But what causes the poles to switch? How often does it happen? How long does it take? And perhaps most important, could it happen again, and what if it did?
All compasses point north, but magnetic north is not the same as the geographic North Pole (you know, the place where the big metal pole that the earth spins on sticks out of the ice). And magnetic north is constantly changing. Its location moved from a spot close to Canada’s Boothia Peninsula in 1831 northward at a rate of about 10 kilometers a year during the 20th century. In recent years it’s sped up to 40 km. per year and is headed for Siberia. Its movement results from the very active interior of our planet.
Molten iron that surrounds the spinning, solid iron inner core of Earth conducts electricity. In turn, this creates a magnetic field, but it’s not all neatly aligned. The ocean of molten iron has currents and vortices and all manner of uneven movement, the result of which is a magnetic field that migrates. It also waxes and wanes in strength over time. Right now it’s fading, about 10% since the 1800s, and in places, ten times faster than scientists would expect. In other areas it’s strengthening. This unevenness has led some to think the poles may be on their way to another switch. Such an occurrence is fairly common, geologically speaking. There have probably been hundreds of them in the last 3 billion years, and we know of 60 of them in the last 20 million years. That’s an average of about once every 300,000 years, but they don’t follow a regular pattern. It’s been 780,000 years since the last one, but that doesn’t mean we are necessarily “overdue.”
When the poles do switch again, as they inevitably will, it will be a slow process by human standards. It takes from hundreds to thousands of years to complete and in the interim there is a bit of a mixed up mess in the field, with poles expressing themselves all over the place. Such wanderings could cause auroral lights to festoon night skies in tropical climates. Some fear chaos during the transition, but the fossil record doesn’t support the idea that a weakened barrier against cosmic and solar radiation (the job of the magnetic field) would allow a mass extinction of life due to the ill effects of exposure. The field gets weak and uneven during a reversal and could allow holes where radiation could be problematic, but it doesn’t disappear altogether. In addition, our atmospheric blanket helps filter out some of the harmful rays. And predictions by some of climate disaster or massive earthquakes resulting from a magnetic flip are not substantiated by sediment records during previous events.
What would be affected pretty strongly would be radio communications, satellites, and GPS systems. Even solar storms can cause disruptions in those technologies. In the natural world, all those species that seem to magically navigate their way across thousands of miles as they migrate might find themselves uncharacteristically confused. But all these changes will come over a long expanse of time and if the bees, birds, whales, and other creatures have weathered past magnetic reversals, surely humans will find a way to cope with the incremental changes that the switching poles would slowly bring.