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. Estimations vary as to the abruptness of the reversal: it may have occurred over several thousand years, or much more quickly, perhaps within a human lifetime.
The apparent duration at any particular location varied from 1,200 to 10,000 years depending on geomagnetic latitude and local effects of non-dipole components of the Earth's field during the transition.
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. 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.