3.6 Earth’s Magnetic Field


How can you find your way?

You can use Earth’s magnetic field to tell you where you want to go. A compass needle aligns with Earth’s magnetic field. People can navigate by finding magnetic north. If you know where north is, you can figure out how to get anywhere. A compass is great for finding your way when you’re out in the field!

Earth’s Magnetism

Earth has a magnetic field (Figure below). The magnetic field behaves like a giant bar magnet inside Earth. If you have a large bar magnet, you can hang it from a string. Then watch as it aligns itself in a north-south direction. It does this to line up with Earth’s magnetic field.

Earth’s magnetic field is like a bar magnet that resides in the center of the planet.

The magnetic field has north and south poles. The magnetic poles do not exactly match the geographic poles. So the magnetic north pole is not the same as the geographic North Pole. The same is true of the South Pole. The magnetic field is created by the movement of molten metal in the outer core.

Earth’s magnetic field extends several thousand kilometers into space. It shields us from harmful radiation from the sun (Figure below).

Earth’s magnetic field protects the planet from harmful radiation.

Magnetic Reversals

Something very strange has happened many times during Earth’s history. The planet’s magnetic field flipped! The North Pole became the South Pole. The South Pole became the North Pole. Scientists are not sure why this happens. The fact that it does happen is useful to scientists. In the concept, “Plate Tectonics,” you’ll learn how.


  • magnetic field: Field produced by a magnetic object. The object exerts a force on other magnetic materials or moving electrical charges.


  • Earth’s magnetic field is like a bar magnet through the planet.
  • The magnetic field is generated by convection in the liquid outer core.
  • Occasionally the magnetic field flips. The North Pole becomes the South Pole and the South Pole becomes the North Pole.

Interactive Practice

Use the resource below to answer the questions that follow.

  1. What aligns itself with the magnetic field in molten rocks as they cool?
  2. What did Brunhes discover about some of the rocks?
  3. What did Brunhes’ discovery mean?
  4. What has happened to the magnetic field in the last century?
  5. What planet is being studied to discover the future of Earth without a magnetic field?


  1. Why does Earth have a magnetic field?
  2. Why is it important for Earth to have a magnetic field?
  3. What is a magnetic reversal?

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