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It would appear that the earth's magnetic poles have 'swapped' many times, with N & S switching positions. If this should happen in the current era, what would be the effect? Obviously all navigational instrumentation would be affected, but what about the effect of a reversal of the magnetic field on electronic devices and electro-magnetic equipment? Would such a massive change affect national power grids?

Excellent question! actually, most modern navigational equipment does not use the Earth's magnetic field because there are many "magnetic anomolies" that cause compasses not to point due north. Geomagnetic reversals are common (on geological time-scales) occurring on average once every 200,000 years. From geological evidence (magnetic fields "frozen" in old rocks) it appears that the reversal process itself takes on order of 1000 years, so the effects would not be noticeable in your lifetime. The evidence also suggests that during this period, the Earth's magnetic field decreases in strength by a factor of 5 or so..

John Hawley

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