 Evidence for these "geomagnetic reversals" can be found in basalts, sediment cores taken from the ocean floors, and seafloor magnetic anomalies.Reversals occur nearly randomly in time, with intervals between reversals ranging from less than 0.1 million years to as much as 50 million years.The most recent geomagnetic reversal, called the Brunhes–Matuyama reversal, occurred about 780,000 years ago.