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Crustal and meteoritic abundances of twenty-two elements plus H2O are compared. Absolute terrestrial abundances of twelve elements (Ba, Ca, Cs, K, La, Na, Rb, Sc, Sr, Th, U, and Y) are inferred from a knowledge of their crustal abundances by extending the recent studies by (1968a) and (1968a, b). Eucritic abundances are consistently higher than the estimated terrestrial ones. Chondritic abundances fall within the limits in all cases except Na, K, and Rb which appear to be depleted in the earth relative to ordinary chondrites by a factor of 0.15 +/- 0.05. This cannot be considered a compelling argument against an earth model with chondritic trace element content, however, because these elements are fractionated in chondritic material to almost the same extent. The possibility that the earth is enriched in refractory elements can neither be confirmed nor ruled out. But the extent of enrichment can be limited; relative to ordinary chondrites it is unlikely to exceed 50 per cent. Carbonaceous chondrite material, stripped of its volatiles, is similarly enriched, by 40-45 per cent; therefore, even if it could be proved that the earth is enriched in refractory elements the chondritic model would still be acceptable.A comparison of eleven volatile elements (Ar, Bi, C, Cs, Hg, In, Kr, N, Pb, Tl, and Xe) in the earth and meteorites indicates that eucrites may not contain enough Ar, Bi, Kr, Tl, and Xe to account for even their crustal abundance. The volatile-element inventory of the earth is remarkably similar to that observed in most chondrites. The data may be interpreted according to either a homogeneous or inhomogeneous accumulation model. If the earth was initially homogeneous, a mean accretion temperature of about 500[deg]K is indicated. Alternatively a thin veneer of carbonaceous chondrite-like material comprising 1-3 per cent of the earth's mass may have been added toward the end of its accretion history. |
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