"Magnetic reversal" redirects here. For switching of a magnet, see Magnetization reversal.
"Polarity reversal" redirects here. For a seismic anomaly, see Polarity reversal (seismology).
A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons.
Reversal occurrences are statistically random. There have been at least 183 reversals over the last 83 million years (on average once every ~450,000 years). The latest, the Brunhes–Matuyama reversal, occurred 780,000 years ago[1] with widely varying estimates of how quickly it happened. Other sources estimate that the time that it takes for a reversal to complete is on average around 7,000 years for the four most recent reversals.[2] Clement (2004) suggests that this duration is dependent on latitude, with shorter durations at low latitudes and longer durations at mid and high latitudes.[2] Although variable, the duration of a full reversal is typically between 2,000 and 12,000 years.[3]
Although there have been periods in which the field reversed globally (such as the Laschamp excursion) for several hundred years,[4] these events are classified as excursions rather than full geomagnetic reversals. Stable polarity chrons often show large, rapid directional excursions, which occur more often than reversals, and could be seen as failed reversals. During such an excursion, the field reverses in the liquid outer core but not in the solid inner core. Diffusion in the outer core is on timescales of 500 years or less while that of the inner core is longer, around 3,000 years.[5]
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and 25 Related for: Geomagnetic reversal information
A geomagneticreversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be...
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the polarity of the Earth's field reverses. These geomagneticreversals, analyzed within a Geomagnetic Polarity Time Scale, contain 184 polarity intervals...
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core. Phenomena associated with these include geomagnetic jerk, westward drift and geomagneticreversals. A secular trend, widely tapered off and in some...
his 1906 discovery of geomagneticreversal. The current period of normal polarity, Brunhes Chron, and the Brunhes–Matuyama reversal are named for him. Brunhes...
event List of geomagneticreversals Herrero-Bervera, Emilio, and S. Keith Runcorn. "Transition Fields during the GeomagneticReversals and Their Geodynamic...
Bradford M. (April 8, 2004). "Dependence of the duration of geomagnetic polarity reversals on site latitude". Nature. 428 (6983): 637–640. Bibcode:2004Natur...
movement of the Indian Plate is an illusion wrought by large errors in geomagneticreversal timing around the Cretaceous–Paleogene boundary, and that a recalibration...
Brunhes (French, 1867–1910) – paleomagnetism; discovered the first geomagneticreversal Walter Hermann Bucher (German-American, 1888–1965) – awarded the...
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Magnetic field reversal may refer to: Geomagneticreversal Brunhes–Matuyama reversal, approximately 780,000 years ago Gauss-Matuyama reversal, approximately...
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periodically reverse their orientation in a process called geomagneticreversal. The most recent reversal occurred 780,000 years ago. The rotating magnetic field...