The Earth´s magnetic field, also known as the geomagnetic field, is an immense invisible shield of magnetic field lines encircling the Earth. The magnetic field protects the Earth from highly charged particles leaving the Sun. The Earth´s magnetic field surrounds planet Earth, extending from the Earth´s outer core to the region where the magnetosphere interacts with the solar wind. The magnetic field is created by electrical currents produced by the convective motion of the iron and nickel at the Earth´s interior. The magnetic north pole is not coincident with the Earth´s axis of rotation, but differs from it by 11º. The magnetic field reverses every few thousands of years, changing its north magnetic pole to south and the south magnetic pole to north.
Origin of Earth´s magnetic field
The Earth´s magnetic field is generated in the core of planet Earth. The field is similar to that of a bar magnet with a north and south poles. The magnetic field lines in the Earth emerge at the South Pole, follow a semicircular path and re-enter at the North Pole. The Earth´s magnetic field is generated by the dynamo effect. The dynamo effect converts mechanical motion produced at the Earth´s liquid outer core, which functions as an electrical generator, into electromagnetic energy. The convective motion of the liquid outer core, driven by the gravitational and thermal forces, is what originates the Earth´s magnetic field.
Scientists think that at various times in the geologic past, the Earth´s magnetic field has totally reversed. In other words, the north magnetic pole has switched to the south and the south magnetic pole has changed to the north. During the time between reversals, the magnetic field loses intensity until it completely disappears, regaining its strength when the positions at the poles are regained. Geologists discovered the existence of the magnetic field reversals by calculating the orientation of the magnetism present in ancient rocks. The magnetic minerals in rocks record whether the magnetic field reverses or remains normal at that time. The last reversal is believed to have occurred 780,000 years ago.
Importance of Earth´s magnetic field
The Earth´s magnetic field is important for all forms of life on the planet. Life on Earth is significantly protected by the natural shield created by the magnetic field. The magnetic field protects the Earth from highly charged particles (solar wind) from the sun. Without the magnetic field, most of the ozone gas, which protects the earth from harmful UV radiation, would be depleted away from the atmosphere. The magnetosphere extends for approximately 10 times the radius of the Earth. The magnetosphere interacts with the solar wind, deflecting it from the path of the Earth. Intense solar wind particles can affect geosynchronous satellites. During severe solar storms, bright displays of light, known as auroras, can be seen at the poles.
The rotation of the Earth on its own axis contributes to the formation of the magnetic field. The Earth´s magnetic field provides the Earth not only protection from the cosmic rays, but it also helps many life forms as a navigation aid. Some birds rely on the magnetic field for travelling long distances while migrating. The Earth´s magnetic field has been used as navigation by humans since ancient times. Planet Venus, which has a core similar to Earth, lacks a magnetic field, supposedly due to its slow period of rotation (243 days). According to NASA, in 2007, scientists found a rupture four times bigger than the Earth in the magnetosphere through which charged solar particles could filter into the magnetosphere. The magnetosphere is a bubble of magnetic field lines that surrounds the earth and protects humans from the solar wind.