The recent progress of the studies on high pressure and high temperature phase transformation of earth materials are reviewed. A brief introduction on the basis on the chemistry and mineralogy of materials composing crust and mantle is also included. Several new high pressure minerals including the post-perovskite phase of MgSiO3, post-stishovite phases of SiO2 such as CaCl2 type, a-PbO2 type phases, which are likely to exist at the core-mantle boundary has been reported. Magma is highly compressible and compatible with iron relative to coexisting minerals, indicating existence of a melt-crystal density crossover at high pressure. The dense melt may play important roles at the core-mantle boundary together with in the early magma ocean stage of the earth's evolution. We can expect existence of gravitationally stable melts in the ultra low velocity layer at the core-mantle boundary. The study of the lower mantle and core is one of the most important target in the material science of the earth.
