The reason why the compass is called a compass is because, except for the North and South Poles, no matter where it is, its two ends always point in the north and south directions respectively. However, the direction of the Earth's magnetic field is not constant. Its north and south magnetic poles have once reversed positions, and the compass has become a compass. This is "magnetic pole reversal." In the billions of years of earth's history, magnetic pole reversal events have occurred many times. In the last 4.5 million years alone, there have been four periods of different magnetic field polarities. There were two times that were basically the same as now, they were "positive periods", that is, the magnetic north pole was near the geographical south pole, and the magnetic south pole was near the geographical north pole. There are two other "reverse periods" that are exactly the opposite of the present. During each magnetic period, brief magnetic pole reversals sometimes occur.
Why do magnetic poles change? Are there any rules for repeated changes in the earth's magnetic field? Scientists have not reached a unified view on this. Most scientists believe that when the flow of liquid iron inside the earth flows around the center of the earth's core, if it suddenly changes and its flow direction reverses, it will cause the magnetic pole reversal phenomenon. The issue of geomagnetic inversion has attracted many geologists and geophysicists, and there are currently two mainstream views. One believes that this magnetic pole reversal is an accidental event and may be caused by convection. If the magnetism of one place inside the earth is suddenly stronger than that of another place, it will push the magnetic force out of the surface, and the magnetic force that pushes it to the surface forms a small magnetic field that will react against the point where the original magnetic force escapes. In this case, a magnetic pole reversal occurs. However, some people believe that the reversal of the Earth's magnetic field is not a random event, but has certain rules to follow and can be predicted. It's just that because the changes in the earth's center are too complex, people have not yet been able to summarize laws similar to fluid movement.