Earth’s most recent geomagnetic reversal — a phenomenon where the planet's overall magnetic field flips — took at least 22,000 years to complete. This is more than twice than previously thought, according to a recent study.

The magnetic field, which protects the Earth from potentially dangerous solar radiation, last flipped some 770,000 years ago and is named Matuyama-Brunhes after the scientists who discovered it, according to the journal Science Advances.

While the final event lasted 4,000 years, it was, however, preceded by another 18,000 years due to an extended period of instability, which included temporary, partial reversals. 

The Matuyama-Brunhes took more than twice as long to flip, while all reversals generally wrap up within 9,000 years, showed the new analysis based on advances in measurement capabilities and a global survey of lava flows, ocean sediments and Antarctic ice cores.

The liquid layer of the Earth called the outer core is responsible for its magnetic field. As Earth spins on its axis, the iron inside the liquid outer core moves around and creates a field.

Reversals of the magnetic field are recorded in the rocks in a phenomenon called rock magnetism. Many rocks contain iron-bearing minerals that act as tiny magnets. As magma or lava cool, these minerals align with the magnetic field preserving its position and form rocks.