The realm of geomagnetism is a new field that has emerged to understand the geological processes along with the Earth’s inner layers. William Gilbert is known as the pioneer of the field of geomorphology. The Earth acts like an enormous magnet that embodies a magnetic north and magnetic south poles. These magnetic poles are situated at the geographic poles. Geomagnetic reversal is a phenomenon of switching positions of the planet’s magnetic dipoles (north and south). The magnetic field of Earth spreads up to 3,200 km. The zone in which the effect of a magnet is felt is called the magnetosphere. This effect is spread over 60,000 kilometres on the Earth’s surface. We can observe the evidence of the switching of the poles in solidified lava or sediments. They preserve a part of the magnetic field at deposition time.

The geomagnetic poles

• As we know that magnets attract opposite sides, the magnetic north pole of the Earth is the south pole of the magnetic field. 
• The magnetic dipole field is normally positioned very close to the rotational axis of the Earth. This means that the magnetic poles are very close to the actual geographic poles of the Earth. 
• The magnetic dipoles of the Earth are nothing but hypothetical intersections of the surface of the Earth and its axis of a bar magnet that is kept at the centre of the Earth.
• It is estimated that the geomagnetic poles are tilted approximately 11 degrees to the rotational axis of the Earth.
• The reason there is a variation between the positions of the geomagnetic and magnetic poles is because of the irregular and compound magnetic field distribution of the Earth.
• The magnetic north pole of the Earth is moving quickly from the Canadian Arctic towards the country of Russia.

Variations of the magnetic field of Earth

• Secular variation: There is a change that happens on the magnetic axis of the Earth once every 960 years. This happens because the Earth spins around on its axis.
• An eleven-year sunspot cycle: There is a particular region on the sun where a very strong magnetic field exists. The Earth faces this region of the sun once every eleven years. 
• Lunar variations: Not only the sun but also the moon effect on the Earth’s magnetic variation.
• Daily and annual variation: The ultraviolet rays ionise the atmosphere of the Earth. As an outcome, a series of currents is generated that produces a variation on a daily and annual basis. 

How often does geomagnetic reversal occur?

The geomagnetic reversals have irregular intervals. These reversals are not spontaneous and occur at random times. They occur for hundreds, thousands, or even millions of years. Hence, it is quite difficult to predict when the next geomagnetic reversal might happen. However, we can observe the reversal in volcanic rocks, especially the rocks that have been retrieved from the ocean floor. From research, it is said that there have been about four to five geomagnetic reversals every one million years. But some eras like the Cretaceous era have not had any no reversals. The time range on how often geomagnetic reversal occurs can be between 10,000 to millions of years. From a paper in the year 2019, it is said that the last reversal was approximately 789,000 years ago and this reversal persisted for 22,000 years.

What causes geomagnetic reversal? 

The reversal of poles on Earth occurs due to the presence of iron molecules in the outer core of the Earth. This happens when the iron molecules that are located in the outer core start going opposite the molecules of iron around them. 

As more and more molecules start going in the opposite direction, this will cause the Earth to experience a geomagnetic reversal. 

The causes for this phenomenon are:

• The magnetic field of Earth and every other planet is created due to the dynamo effect. The dynamo effect occurs due to the molten iron present in the core of the planet that creates currents of electricity. These currents of electricity produce magnetic fields. 
• In the planetary dynamo simulations, the magnetic reversal appears instantaneously from underlying dynamics. 
• Some researchers like Richard A. Muller say that reveals are not instantaneous. It is triggered by the events that occur externally. These events will directly interrupt the flow of molten iron in the core of the Earth. 
• Other researchers have proposed that the events that happen internally like the arrival of slabs of continents that are brought down to the mantle because of plate tectonics.
• The supporters of this hypothesis say that this phenomenon can lead to disrupting the dynamo which can turn off the geomagnetic field. 

Conclusion

This article has answered questions about geomagnetic reversals such as How often does geomagnetic reversal occur and What are the causes of it? The magnetic field of Earth spreads up to 3,200 km. The zone in which the effect of a magnet is felt is called the magnetosphere. We can observe the evidence of the switching of the poles in solidified lava or sediments. They preserve a part of the magnetic field at deposition time. There are variations of magnetic fields such as secular variation, an eleven-year sunspot variation, lunar variation, and daily and annual variation. These reversals are not spontaneous and occur at random times. They occur for hundreds, thousands, or even millions of years. It is said that the last reversal was approximately 789,000 years ago and this reversal persisted for 22,000 years. The reversal of poles on Earth occurs due to the presence of iron molecules in the outer core of the Earth.