CHEMICAL COMPOSITION OF THE EARTH AND THE VOLATILITY CONTROL ON PLANETARY GENETICS

Abstract

Using trace element ratios with a common reference to a refractory element, we have shown that carbonaceous chondrites define a straight line in every diagram including the semi-volatile and volatile elements with the relative position of CI, CM, CO and CV always following the same order. We show that bulk Earth values estimated only by terrestrial consideration, using Mg/Al for the refractories or K/U, Rb/Sr for the volatiles, plot on the carbonaceous chondrite line but not within the group of ordinary chondrites. The position on the carbonaceous chondrite line varies according to volatility. Highly refractory elements are close to CI, moderate refractories close to CM and volatiles away from CV. Such systematics permit the calculation of the bulk composition of the Earth for every element. Those observations are in agreement with a condensation temperature of the Earth ranging from 11 to 1200°K.