A University of California, Berkeley, geophysicist has made the first-ever measurement of the strength of the magnetic field inside Earth’s core, 1,800 miles underground.The magnetic field strength is 25 Gauss, or 50 times stronger than the magnetic field at the surface that makes compass needles align north-south. Though this number is in the middle of the range geophysicists predict, it puts constraints on the identity of the heat sources in the core that keep the internal dynamo running to maintain this magnetic field.

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