The Brunhes-Matuyama Reversal was a geologic event, approximately 780,000 years ago, when the Earth's magnetic field last underwent reversal. The reversal occurred over several thousand years. 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 event is useful in dating ocean sediment cores and subaerially erupted volcanics. It is named after Bernard Brunhes and Motonori Matuyama.