The huge magnetic field which surrounds the Earth, protecting it from radiation and charged particles from space—and which many animals even use for orientation purposes—is changing constantly, which is why geoscientists keep it constantly under surveillance. The old well-known sources of the Earth’s magnetic field are the Earth’s core—down to 6,000 kilometres deep down inside the Earth—and the Earth’s crust: in other words, the ground we stand on. The Earth’s mantle, on the other hand, stretching from 35 to 2,900 kilometres below the Earth’s surface, has so far largely been regarded as “magnetically dead.” An international team of researchers from Germany, France, Denmark and the U.S. has now demonstrated that a form of iron oxide, hematite, can retain its magnetic properties even deep down in the Earth’s mantle. This occurs in relatively cold tectonic plates, called slabs, which are found especially beneath the western Pacific Ocean.
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Source: Phys.org