“Reversals have been documented as far back as 330 million years. During that time more than 400 reversals have taken place, one roughly every 700,000 years on average. However, the time between reversals is not constant, varying from less than 100,000 years, to tens of millions of years. In recent geological times reversals have been occurring on average once every 200,000 years, but the last reversal occurred 780,000 years ago. At that time the magnetic field underwent a transition from a “reversed” state to its present “normal state”.”
780,000 years ago- Looks like we are about due. 2012?
http://www.slowmotiondoomsday.com/polarpivot.html
Man, that 2012 date just keeps poppin up.
“Effects on biosphere and human society”
“Because the magnetic field has never been observed to reverse by humans with instrumentation, and the mechanism of field generation is not well understood, it is difficult to say what the characteristics of the magnetic field might be leading up to such a reversal. Some speculate that a greatly diminished magnetic field during a reversal period will expose the surface of the earth to a substantial and potentially damaging increase in cosmic radiation. However, Homo erectus and their ancestors certainly survived many previous reversals. There is no uncontested evidence that a magnetic field reversal has ever caused any biological extinctions. A possible explanation is that the solar wind may induce a sufficient magnetic field in the Earth’s ionosphere to shield the surface from energetic particles even in the absence of the Earth’s normal magnetic field.[7]
Although the inspection of past reversals does not indicate biological extinctions, present society with its reliance on electricity and electromagnetic effects (e.g. radio, satellite communications) may be vulnerable to technological disruptions in the event of a full field reversal.”
Leave it to Wiki to calm our fears.