The Earth’s magnetic field

In short: The Earth is surrounded by a magnetic field that aligns compass needles and protects us from some of the charged particles coming from space.

In more detail: The field is generated in the liquid outer core. Molten iron and nickel flow there, and this movement of electrically conducting melt produces electric currents and thus a magnetic field, much like a dynamo (the geodynamo).

In detail

• Like a bar magnet: As a rough approximation, the field resembles that of a large bar magnet inside the Earth, tilted slightly relative to the Earth’s axis.
• Swapped poles: The north pole of a compass needle points north. Physically, then, there is a magnetic south pole there, even though it is commonly called the magnetic North Pole.
• Declination: The magnetic and geographic poles are not in the same place. The difference between compass direction and true north is called declination and varies from place to place.
• Wandering poles: The magnetic poles move constantly, sometimes by many kilometres a year. Maps and navigation systems are therefore updated regularly.
• Reversals: Over Earth’s history the field has flipped many times, at irregular intervals. The last complete reversal was about 780,000 years ago.
• Traces in rock: Cooling lava records the direction of the field at the time. Striped patterns on the seabed thus helped to confirm plate tectonics.
• Protective shield: The magnetosphere deflects much of the solar wind. When particles enter the atmosphere near the poles, auroras appear.
• Animal navigation: Many migratory birds, sea turtles and other animals can sense the magnetic field and use it to find their way.
• Further reading: Compasses, auroras and magnetism are closely linked (kompass-und-himmelsrichtungen, polarlichter, magnetismus-grundlagen).