Two recent forms of velocity-density relations have been inverted using Earth models derived from free-oscillation data to infer mean atomic weight profiles for the mantle. Within present uncertainty there is no evidence for discontinuities in mean atomic weight ; from below the crust to just above the core-mantle boundary. The best value for a constant is 21.1 ± 0.4 g/mole. Uniform is consistent with whole-mantle convection and with diminished total iron content of the Earth. Because the mean atomic weight profiles are sensitive to small differences among the normal-mode Earth models, further refinement of these models is of great interest.

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