Polumkehrung

Polumkehrung, also known as magnetic pole reversal or geomagnetic reversal, is a fundamental process that occurs over geological timescales in the Earth's magnetic field. This phenomenon involves the significant weakening, and eventual disappearance, of the Earth's main dipole magnetic field, followed by its regeneration in the opposite direction. The North Magnetic Pole becomes the South Magnetic Pole, and vice versa.

The Earth's magnetic field is generated by the movement of molten iron and nickel in the planet's outer core, a process known as the geodynamo. The exact mechanisms that trigger a polumkehrung are still a subject of scientific research, but it is understood that instabilities within this geodynamo are responsible.

Evidence for past polumkehrungen comes primarily from paleomagnetism. Rocks formed at the Earth's surface, especially volcanic rocks that cool from a molten state, record the direction and intensity of the magnetic field at the time of their formation. By studying these magnetic signatures in rock layers of different ages around the world, scientists have compiled a detailed history of magnetic reversals.

The frequency of polumkehrungen is irregular. They can occur with intervals ranging from tens of thousands to millions of years. The last full reversal, known as the Brunhes–Matuyama reversal, occurred approximately 780,000 years ago. While the Earth's magnetic field is currently weakening, and some scientists believe we may be approaching a reversal, the timing and process remain uncertain. A polumkehrung itself is not instantaneous; it can take thousands of years to complete.