phase transitions in the mantle

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phase transitions in the mantle Measurement of the velocity of seismic waves and determination of the Earth's moment of inertia indicate that at depths of 80–100 km there appears to be a low-velocity zone and from 400–900 km velocities increase more rapidly than had been expected. These variations in the mantle may be due to changes in composition or to phase change, e.g. a transition to a cubic form of olivine.