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Politics : The Environmentalist Thread

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To: longnshort who wrote (6205)4/7/2006 11:58:19 AM
From: average joe  Read Replies (1) of 36917
 
A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events, which typically last a few hundred to a few thousands years, often involve an extended decline in field strength followed by a rapid recovery after the new orientation has been established.

Over very long periods, geomagnetic reversals seems to have occurred with a frequency of 1 to 5 events per million years; however, this duration is highly variable. During some periods of geologic time (e.g. Cretaceous long normal), the Earth's magnetic field is observed to maintain a single orientation for tens of millions of years. Other events seem to have occurred very rapidly, with more than one reversal in 50,000 years. The last reversal was the Brunhes-Matuyama reversal approximately 780,000 years ago.

en.wikipedia.org
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