Magnesium bulk Earth composition

As regards the rock-forming elements, the bulk composition of the Earth is basically chondritic (i.e., solar) with approximately equal abundances of magnesium, sihcon, and iron atoms. In detail, however, there are some variations in chemistry among chondritic meteorites, and from a detailed comparison with meteorites it is concluded that the bulk Earth composition has similarities with the chemical composition group of carbonaceous chondrites. 

For this review the Earth s composition will be considered to be more similar to carbonaceous chondrites and somewhat less like the high-iron end-members of the ordinary or enstatite chondrites, especially with regard to the most abundant elements (iron, oxygen, silicon, and magnesium) and their ratios. However, before reaching any firm conclusions about this assumption, we need to develop a compositional model for the Earth that can be compared with different chondritic compositions. To do this we need to (i) classify the elements in terms of their properties in the nebula and the Earth and (2) establish the absolute abundances of the refractory and volatile elements in the mantle and bulk Earth. 

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