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3.3: Earth's Magnetic Field

  • Page ID
    5341
  • 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

    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 North Magnetic 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).

    Drawing of the Earth's magnetic field deflecting the solar wind

    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 Magnetic Pole became the South Magnetic Pole. The South Magnetic Pole became the North Magnetic Pole. Scientists are not sure why this happens. The fact that it does happen is useful to scientists. In the chapter Plate Tectonics, you'll learn how.

    Summary

    • 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 Magnetic Pole becomes the South Magnetic Pole and the South Magnetic Pole becomes the North Magnetic Pole.

    Review

    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 field reversal?

    Explore More

    Use this resource to answer the questions that follow.

    1. What generates Earth’s magnetic field? Why is the magnetic field important?
    2. What is a magnetic field flip? Roughly how often does it happen?
    3. Why do scientists interested in Earth’s magnetic field collect cores from rocks at the Mid-Atlantic Ridge?
    4. When was the last major magnetic field flip?
    5. How do ancient pottery give scientists clues about Earth’s magnetic field? Why is it more precise than rocks?
    6. When was Earth’s magnetic field strength high and when was it lower (note that BCE means before current era and years correlate with the BC and AD system)?
    7. What has happened to magnetic north since it was first located in the early 19th century? How has the field changed in the past two centuries?
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