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  • BBC Science Focus Magazine

    THE EXPLAINER

    Oct 06, 2021 3 minutes
    by MARCUS CHOWN

    WHAT CAUSES EARTH’S MAGNETIC FIELD?

    Magnetic fields are generated by electric charges in motion. In a bar magnet, the moving charges are electrons orbiting in atoms. In the Earth, they are electrons ferried around by circulating currents of molten iron.

    The details are not well understood. But, basically, hot material in Earth’s outer liquid iron core expands, becoming less dense than its surroundings, and therefore rises. Cooling and becoming less dense, it should sink back down again.

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