Modern high-pressure experimental techniques have enabled us to achieve the pressure and temperature at the center of Earth (about 360 GPa and 6000 K) in laboratories. However, studies of rheological properties of minerals under controlled strain rate (creep experiments) have been limited to the pressure equivalent to that in Earth's transition zone, a depth only about one-tenth of Earth's radius. Determinations of rheological laws that govern the flows and viscosities of minerals in Earth's deep mantle have been far beyond our reach. In the absence of such critical data, the nature of mantle dynamics—such as whether the convection involves the entire lower mantle, yielding a chemically homogeneous deep mantle—remains controversial.
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