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The Earth's Magnetic Field


Our planet Earth is surrounded by an immense magnetic field that extends from the Earth’s interior into the space. The origin of the Earth’s magnetic field is still not fully understood, but it is thought to be a result of the molten iron and nickel in the Earth’s outer core. Heat escapes from the Earth's core and causes natural convection in the outer core. These rotating, convecting, and electrically conducting currents generates the Earth's magnetic field. This effect is known as the dynamo effect or the geodynamo. It provides a theory of how the Earth’s magnetic field is sustained.











The Earth’s magnetic field at its surface can be approximated as a magnetic dipole placed in the centre of the planet, forming two poles: the North and the South. These poles have opposite positive and negative polarities, like a bar magnet. However, this bar magnet is slightly tilted with respect to the Earth’s rotation axis, which means the geographic and magnetic poles are not located in the same place. Additionally, the North and South magnetic poles slowly and continuously move over. 

Interestingly, what we know as ‘Magnetic North’ or ‘Magnetic North Pole’ that is situated in the geographic north represents the South pole of the Earth’s magnetic field. Contrarily, the ‘Magnetic South’ or ‘Magnetic South Pole’ situated in the geographic south pole corresponds to the North pole of Earth’s magnetic field. As opposite magnetic poles attract, the north end of a magnet will point towards the south pole: A compass needle (north pole) will always point to the Earth’s South magnetic field, which is the Magnetic North situated close to the geographic Earth’s North Pole.

The Earth’s magnetic field is dynamic and can change for short or long periods. During magnetic storms, for example, it can change quickly. The magnetic field acts as a shield from the charged particles emitted by the Sun, known as the solar wind. When the charged particles collide with the Earth’s atmosphere, they excite the oxygen, nitrogen and hydrogen atoms, creating the beautiful aurora. Depending on the pole, they are known as aurora borealis (north) and aurora australis (south). Long-term changes occur when the Earth’s magnetic field reverses: magnetic north and south poles swap locations. Pole reversals are common in Earth’s geologic history. This event happened 183 times in the last 83 million years, every 300,000 years or so, with the last one taking place about 780,000 years ago.

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