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Periodicity of the Earth's magnetic reversals


Reversals of the Earth's magnetic field may occur with a certain regularity. Using observed percentages of normal and reversed polarity during different time intervals, Negi and Tiwari1 detected several significant periodicities, notably one of 32–34 Myr. Raup2 used the dates of individual reversals to propose a 30-Myr period in the frequency of reversals, although Mazaud et al.3 obtained a periodicity of only 15 Myr. Like Negi and Tiwari's1 other detected short periods, the 15-Myr period may be harmonically related to a basic 30-Myr period4. It has also been suggested that these are accidental periodicities arising in a short record5,6, or are harmonics of the record length itself7. In fact, all of the cited studies have used different data, different record lengths and different methods of time-series analysis. Raup8 has consequently retracted his original claim. Here I present a much fuller analyis of the reversal record and show that a statistically significant period of 30 Myr does formally exist, in spite of the cited differences.

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Stothers, R. Periodicity of the Earth's magnetic reversals. Nature 322, 444–446 (1986).

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