Magnetic field reversal is a phenomenon where the Earth's magnetic poles switch places. This occurs irregularly, approximately every 200,000 to 300,000 years, although the last reversal, called the Brunhes-Matuyama reversal, happened around 780,000 years ago. During a reversal, the magnetic field can weaken, leading to temporary gaps and increased radiation exposure on Earth. Understanding magnetic field reversals helps scientists learn about the Earth's interior dynamics and provides insights into the planet's geological history.