A phase transition of MgSiO3 perovskite, the most abundant component of the lower mantle, to a higher-pressure form called post-perovskite was recently discovered for pressure and temperature conditions in the vicinity of the Earth's core-mantle boundary. This discovery has profound implications for the chemical, thermal, and dynamical structure of the lowermost mantle called the D” region. Several major seismological characteristics of the D” region can now be explained by the presence of post-perovskite, and the specific properties of the phase transition provide the first direct constraints on absolute temperature and temperature gradients in the lowermost mantle. Here we discuss the current understanding of the core-mantle boundary region.

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