Earth Magnetic Reversal Frequency

Studies of magnetization orientations in magnetic minerals in the earth have revealed that earth's magnetic field has reversed polarity hundreds of times over the past 150 million years and that the frequency of reversals, although somewhat random, has been generally increasing over the past 90 million years. The reason for the frequency increase is not known. However, one theory is that the frequency is increasing as the inner core of the earth gradually cools which reduces the energy driving turbulent vortices in the outer core which produce earth's magnetic dipole. The dipole polarity has been in its present state for a considerably longer time than an average taken over recent cycles, adding to other evidence that the next reversal either has already started or will start soon. ©2005 Tigertek, Inc. All rights reserved.

• April Fact-of-the-Day Index