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BookmarkScienceDaily (Nov. 7, 2006) — The average rate of Earth's geomagnetic reversals has varied enormously, from five reversals per million years during the last 10 to 20 million years to as low as 0.05 reversals every million years between 125 and 84 million years ago.
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Why such a large variation over this time?
In an article published recently in the journal Geophysical Research Letters, R. S. Coe and G. A. Glatzmaier, of the Department of Earth and Planetary Sciences and Institute of Geophysics and Planetary Physics, University of California, Santa Cruz, analyzed computer simulations of the geodynamo, the process by which magnetic field is produced by the Earth's convecting core.
They found that geodynamos that produced highly equatorially symmetric fields were much less stable than those that produced highly asymmetric fields, consistent with earlier studies based on the paleomagnetism recorded by volcanic rocks.
Further, a simulation with a solid inner core much smaller than today's produced a very asymmetric field, suggesting that reversals were much less common in the distant geologic past than in the more recent past. Though not definitive, because of the paucity of suitable continuous sections, the authors' review of paleomagnetic results from ancient rocks offers independent support for this conjecture.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027903, 2006
