Friday, 3 September 2010

Polar opposites

Every so often throughout the history of the Earth, its geomagnetic field has switched. Magnetic North and magnetic South swap seats. There's no discernible occurrence pattern - gaps between flips range from a few thousand years to tens of millions of years. The process usually takes quite some time, say 4,000 - 10,000 years, as the field weakens slowly, then switches and regains strength at a faster rate. Rocks in a site in Nevada appear to show the process can happen far more quickly, though, and this is not the first such find. A 1995 paper on a site in Oregon showed similar findings, but the suggestion has proved controversial.

The field is generated by the movement of iron-rich molten rock beneath the Earth's surface. There is a system of convection currents moving the magma around and changes in the flow may result in disruption to the magnetic field. The flow can be influenced by the absorption of subducted slabs of crust material, but also possibly by meteorite impacts, major episodes of vulcanism, earthquakes and so on. There may be another, weaker field produced by the iron in the crust layers, too.

Currently, the field is weakening and has been for over 100 years. The rate of weakening has risen recently and this may suggest we are heading towards a flip. Or it may not, as it may just regain strength. Again, these fluctuations happen all the time, and it is still well within 'normal' limits. As it seems to be completely random, we cannot say we are due for another soon, but there is a theory that it will happen in 2012. Seems far too specific to me, and unlikely for that reason alone.

Whether in two years or not, it will happen at some point. How is it going to affect humanity? Some think the weakened field will expose the Earth and all its inhabitants to harmful cosmic radiation. Safe to say that - as we are all still here - humans have survived many flips in the past and there's no reason to expect dramatic changes in our life. Like death rays from space. There don't appear to be any extinction events linked to any previous flip. We may have to abandon our compasses for a bit, that's all.

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