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The Earth's innards may steer seismic waves in stranger ways than scientists anticipated.

Jung-Fu Lin of Lawrence Livermore (Calif.) National Laboratory and his team performed a lab experiment on ferropericlase—a mixture of iron and magnesium oxides that makes up about 20 percent of Earth's mantle. They found that in the conditions that exist from 1,000 to 2,200 kilometers below Earth's surface, the material's magnetic properties steadily change.

The gradual transition is due to a tighter packing of electrons in ferropericlase, which slightly increases its density, Lin says. For reasons that are poorly understood, the rearrangement also affects the propagation speed of seismic waves.

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