THE INTEGRAL ENSTATITE CHONDRITE MODEL OF THE EARTH

The only primitive meteorites that match satisfactorily both the stable isotope and redox characteristics of the Earth are the Enstatite chondrites. I present an integral Enstatite chondrite model in which the Earth is built from essentially pure EH material, which is justified by the above similarities and by the fact that most elements in these meteorites exist in very refractory phases, more so than in most other types of meteorites. This results in a rather strong chemical heterogeneity at the upper-lower mantle boundary, which favours a two-level mantle convection model and puts limitations on the chemical relationships between lower and upper mantle. The upper mantle differentiation from EH material calls for a more complex mechanism than simple liquid metal sinking, involving a two-step redox mechanism, governed by pressure and temperature variations, during which the Enstatite-Perovskite transition plays a major role. A very late accretion of 0.8% of CI type material takes into account the stable isotope differentiation of the Upper Earth (upper mantle plus outer envelopes).