The Earth’s interior remains unexplored to a great extent. Only a small number of constituents from different levels can be extracted and analyzed at ambient conditions. Therefore, our understanding of the composition of the Earth by direct observation is quite limited and subject to other indirect methods leading to a changing knowledge, which needs to be constantly updated in view of new evidence. There are three fundamental approaches providing information to be compared and complemented to establish our view of the
materials and processes inside the Earth. The first one arises from the seismic data which reveal the pressure distribution, density and elasticity moduli as a function of depth. There are also thermal models, influenced by different thermodynamic parameters, which play a fundamental role in establishing correlations between temperature and pressure of minerals at different depths. Finally, compositional models give us information about the distribution of constituents in minerals for particular pressure and temperature conditions. These depend on thermal and seismological models .