The Earth´s magnetic field (geomagnetic field) is an enormous invisible shield of magnetic field lines surrounding the Earth. The magnetic field protects the Earth from the charged particles (solar wind) coming from the Sun. The magnetic field extends from the Earth´s liquid outer core to the outer limits of the magnetosphere. The field is generated by electrical currents stemming from the convective motion of the Earth´s interior liquid outer core of iron and nickel (dynamo effect). The magnetic north pole diverges from the Earth´s rotational axis by 11º. At time intervals of thousands of years, the Earth´s magnetic field reverses its poles. The north pole becomes south and the south pole becomes north.
The magnetic field originates in the liquid outer core of the planet. It is believed that this field is the result of electrical currents produced by convective motions of iron and nickel of which the outer core is composed. The generation of the magnetic field by convective motions is known as the dynamo effect. The dynamo effect converts convective motions of iron and nickel, occurring in the Earth´s outer liquid core, into electromagnetic energy. It is thought that the Earth´s rotation contributes to the generation of the Earth´s magnetic field, as planet Venus, whose core is composed of iron and nickel, does not have a magnetic field due to its slower rotation (243 days).
Earth´s magnetic field varies and the location of the magnetic poles reverse over time. Every few thousands of years, the Earth´s magnetic field changes intensity and flips over. The Earth´s magnetic field has alternating periods of normal polarity and reverse polarity. The periods of normal and reverse polarity are called ¨chrons.¨ Chrons have a time span of between 0.1 and 1 million years, and an average time span of 450,000 years. Magnetic field reversals are estimated to occur from 1,000-10,000 years. The most recent reversal occurred 780,000 years ago; however, a recent study revealed that a reversal may have occurred 41,000 years ago during the last glacial period.
The reversals of the magnetic poles allow paleomagnetists to calculate the motion of the continents on the past. Studies made on young rocks have revealed that the Earth´s magnetic poles flip over periods of hundreds of thousands of years. Normally, the magnetic poles are coincident with the Earth's south and north poles. This coincidence is used to estimate the direction of remnant magnetism in ancient rocks at the time of the rock´s formation with respect to the north and south poles. The study of the remnant magnetism in ancient rocks can reveal the magnetic inclination and declination, which estimate the direction and distance of the rock with respect to the pole at the time when the rock was magnetized.
The Earth´s magnetosphere is created due to the interaction between the Earth´s magnetic field and the solar wind. The Earth´s magnetosphere extends out into space to about 10 times the Earth´s radius 63,731 km (39,123 miles). The Earth´s magnetosphere protects the planet from the sun´s solar wind (very high charged particles). The Earth´s magnetic field is compressed by the solar wind on its daylit side to a distance of about 65,000 km (40,000 miles). On the night side of the Earth´s magnetic field, the flow of charged particles produces a magnetotail that extends for more than 6 million km (7,20,000 miles).
The Earth´s magnetic field helps life forms on Earth in varied ways. The magnetic field protects the Earth from harmful charged particles coming from the Sun and it also aids the migration pattern of some animals. Birds are known to use the Earth´s magnetic field to navigate great distances during migration. Turtles are believed to use both direction and intensity of the magnetic field in navigation. According to NASA, the Earth´s magnetic field is moving at an average of 10 km (6.2 miles) per year; moreover, the magnetic field has weakened by 10% since the 19th century.