Of a perovskite may solve some mysteries near the core-mantle boundary halfway to Earth’s center. Just above that boundary, the so-called D″ layer exhibits a puzzling seismic discontinuity in which an elastic wave’s speed varies significantly with direction. When scientists from the Tokyo Institute of Technology placed the perovskite form of MgSiO3 in a diamond anvil cell and subjected it to temperatures and pressures similar to those of the D″ layer, the mineral changed to a new crystalline form. By running molecular-dynamics simulations, the researchers found that only a slightly denser and highly anisotropic crystalline structure, dubbed post-perovskite, could fit their x-ray data. Because perovskite is plentiful in the deep mantle, the researchers say that the newfound form can explain some of the seismic irregularities. Using the Tokyo x-ray data, a University of Minnesota group led by Renata Wentzcovitch ran independent simulations and presented similar conclusions at the March...

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