CHONDRITE MODELS FOR THE COMPOSITION OF THE EARTHS MANTLE AND CORE

The terrestrial planets of the inner Solar System are believed to be b roadly chondritic in composition. Here I suggest that the lithophile e lement composition of the terrestrial mantle, as approximated by primi tive lherzolites having high Al/Si ratios and low Mg/Si ratios, was es tablished by nebular rather than indigenous processes. The implication s of this model include: (i) the Mg/Si ratio of the upper mantle is an intrinsic property of the bulk Earth and does not reflect differentia tion of a terrestrial magma ocean; (ii) the Moon probably did not form by a giant impact on to the Earth; (iii) refractory lithophile elemen ts should be 2.5-3.0 chondrites in the bulk silicate Earth; and (iv) s ilicon is not a major constituent of the Earth's core.