Brunhes–Matuyama reversal

The Brunhes–Matuyama reversal, named after Bernard Brunhes and Motonori Matuyama, was a geologic event, approximately 781,000 years ago, when the Earth's magnetic field last underwent reversal.[1][2] Estimations vary as to the abruptness of the reversal. A 2004 paper estimated that it took over several thousand years;[3] a 2010 paper estimated that it occurred more quickly,[4][5][6] perhaps within a human lifetime;[7] a 2019 paper estimated that the reversal lasted 22,000 years.[8][9]

The apparent duration at any particular location can vary by an order of magnitude, depending on geomagnetic latitude and local effects of non-dipole components of the Earth's field during the transition.[3]

The Brunhes–Matuyama reversal is a Global Boundary Stratotype Section and Point (GSSP), selected by the International Commission on Stratigraphy as a marker for the beginning of the Middle Pleistocene, also known as the Ionian Stage.[10] It is useful in dating ocean sediment cores and subaerially erupted volcanics. There is a highly speculative theory that connects this event to the large Australasian strewnfield (c. 790,000 years ago),[11] although the causes of the two are almost certainly unconnected and only coincidentally happened at the same time.