A geomagnetic reversal is a phenomenon where the Earth's magnetic field changes direction, causing the magnetic north and south poles to switch places. This process occurs over thousands of years and is recorded in geological formations, such as volcanic rocks and ocean floor sediments. Scientists study these reversals to understand the history of the Earth's magnetic field and its impact on the planet. During a geomagnetic reversal, the strength of the magnetic field may weaken, which can expose the Earth to increased solar and cosmic radiation. While these events have occurred many times throughout Earth's history, they do not happen on a predictable schedule. The last major reversal, known as the Brunhes-Matuyama reversal, occurred approximately 780,000 years ago.