page_title: Geomagnetic reversal
hierarchical_section_title: Geomagnetic reversal
context_page_description: A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. 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 183 reversals over the last 83 million years. The latest, the Brunhes–Matuyama reversal, occurred 780,000 years ago, 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 7000 years for the four most recent reversals. Clement suggests that this duration is dependent on latitude, with shorter durations at low latitudes, and longer durations at mid and high latitudes. Although variable, the duration of a full reversal is typically between 2000 and 12000 years, which is one to two orders of magnitude less than the duration of magnetic chrons.
context_section_description: 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 183 reversals over the last 83 million years. The latest, the Brunhes–Matuyama reversal, occurred 780,000 years ago, 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 7000 years for the four most recent reversals. Clement (2004) suggests that this duration is dependent on latitude, with shorter durations at low latitudes, and longer durations at mid and high latitudes. Although variable, the duration of a full reversal is typically between 2000 and 12000 years, which is one to two orders of magnitude less than the duration of magnetic chrons.
  Although there have been periods in which the field reversed globally (such as the Laschamp excursion) for several hundred years, 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 liquid outer core is on timescales of 500 years or less, while that of the solid inner core is longer, around 3000 years.
caption: Geomagnetic polarity during the last 5 million years (Pliocene and Quaternary, late Cenozoic Era). Dark areas denote periods where the polarity matches today's normal polarity; light areas denote periods where that polarity is reversed.