Earth Science: The Magnetic Field of The Earth
What do a compass needle pointing north, the glowing veils of polar lights and the sense of direction of carrier pigeons have in common? All three are influenced by the invisible force of the Earth’s magnetic field.
The Earth’s magnetic field is like a gigantic bar magnet tilted at 11° to the rotational axis of the Earth. Therefore the position of the magnetic poles deviates from the geographical North and South Poles. The magnetic poles are constantly moving. The magnetic north pole was on the Canadian Boothia Peninsula when it was discovered in 1831, but since then it has moved about 685 miles (1,100 km), heading with increasing speed in the direction of Siberia.
The origin of the magnetic field lies in the interior of the Earth and is produced by enormous convection cur- rents within the liquid outer core of the Earth. At depths between 1,800 to 3,200 miles (2,900 to 5,150 km), liquid iron churns around the solid iron inner core of the Earth. This movement creates an electric field, and thus the accompanying magnetic field-a phenomenon also referred to as a geodynamo.
Invisible protective shield
The magnetic field of the Earth extends into space, where it is called the magnetosphere. It protects the planet against cosmic radiation—especially the lethal rays of the solar wind, which are directed around the field. The magnetic field lines are compressed on the side facing the sun and extend, tail-like, on the other side.
North becomes south
Magnetized rocks from the early history of the Earth date the magnetic field to at least 3.5 billion years. These rocks also indicate that the magnetic field has repeatedly collapsed and reversed its polarity. On average, such a repolarization occurs every 500,000 years.
During the actual reversal of polarity, the protection of the magneto- sphere is temporarily lost. The last time the magnetic north and south poles changed their position was about 780,000 years ago. Therefore, another reversal is already overdue.
BASICS
VAN ALLEN BELT Zones with a high density of electrically charged particles that surround the Earth at altitudes of 620-3.100 or 9,320-15,530 miles (1,000-5,000 or 15.000-25.000 km).
MAGNETOPAUSE The boundary of the magnetosphere. which extends about 37.300 miles (60.000 km) on the side directed toward the sun; on the other side it ends about 3.1 million miles (5 million km) from the Earth