In the early 20th century, geologists first noticed that some volcanic rocks were magnetized opposite to the direction of the local Earth's field.41,000 years ago, a complete and rapid reversal of the geomagnetic field occured.That reversal lasted only about 440 years with the actual change of polarity lasting around 250 years.During this change the strength of the magnetic field weakened to 5% of its present strength.
In fact, at the rate we’re moving right now, we won’t cross into the center of the galactic plane for another few hundred thousand years, much less by December of 2012.
The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago; and may have happened very quickly, within a human lifetime.
A brief complete reversal, known as the Laschamp event, occurred only 41,000 years ago during the last glacial period.
Most reversals are estimated to take between 1,000 and 10,000 years.
The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago.
A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged.