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Nature 446, 623-625 (5 April 2007) | doi:10.1038/446623a; Published online 4 April 2007

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Palaeomagnetism: A more ancient shield

David J. Dunlop1

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Earth's magnetic field has protected our atmosphere from erosion by the solar wind ever since it started up. Silicate crystals from some of Earth's oldest rocks date that event to more than 3 billion years ago.

Most planetary magnetic fields originate from the movement of electrically conducting fluid in the planet's interior: Earth's own magnetic dynamo lies deep in its hot, convecting core of liquid iron. The resulting global magnetic field protects Earth's atmosphere from depletion by the solar wind, a continuous, but highly variable, stream of charged particles ejected from the Sun.

  1. David J. Dunlop is in the Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada.
    Email: dunlop@physics.utoronto.ca

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