Magnetic reversal, also known as geomagnetic reversal, is a phenomenon where the Earth's magnetic field changes direction. This means that the magnetic north and south poles switch places. These reversals occur over thousands to millions of years and are recorded in the geological layers of rocks, particularly in volcanic and sedimentary formations. The last major magnetic reversal, called the Brunhes-Matuyama reversal, happened about 780,000 years ago. While the exact cause of these reversals is not fully understood, they are believed to be linked to movements in the Earth's outer core, where molten iron generates the magnetic field.