|MadSci Network: Earth Sciences|
No, the earth did not flip over, only the polarity of its magnetic field changed. The earth's magnetic field is internally generated, by circulation patterns in the liquid iron outer core. The earth's magnetic field behaves as if the earth were a big bar magnet, but unlike bar magnets, the earth is not permanently magnetized. The vast majority of the earth, including all of the metallic iron parts, are much too hot to be permanently magnetized (Metal magnets loose their permanent magnetism above a temperature called the Curie point - for Fe-oxides this is about 500-600 degrees C). The polarity reversals on earth have something to do with changes in the core circulation, but to my knowledge, the details of the mechanisms are still unknown and are the subject of continuing research. For example, see the recent paper: Narteau, C. ; Blanter, E. ; Le Mouel, J. L. ; Shirnman, M. ; Allegre, C. J. , 2000, Reversal sequence in a multiple scale dynamo mechanism. Physics of the Earth and Planetary Interiors, v. 120, no. 4 p. 271-287. Someone at the University of Richmond might be able to help you find this paper and others on the same topic. This paper is written for professionals in the field to read and you may have a very hard time following the details, but you might be able to find useful information in the introduction and conclusion sections. In this paper, the authors use a dynamo model (electro-magnetic fields generated by circulating fluids) to successfully reproduce many of the features of earth's field, including reversals, which appear to be generated by feedbacks between the field and the motions of the fluids generating the field. For a scientifically rigorous explanation that is a little more accessible, see this web site: http://ees5-www.lanl.gov/IGPP/Geodynamo.html What happens when the field reverses is well known from detailed studies of rock sequences at the times of reversals. The strength of the magnetic field decreases to zero and then increases again with the opposite polarity (compasses would point in the opposite direction). Other than the malfunctioning of compasses, everything else would be perfectly normal and the effects on life would be negligible. Dave Smith La Salle University, Philadelphia, PA
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