the crustal Na content and chemical buoyancy force through a linear fit of these values for only those 609 stars that were within the MELTS database and in the @Adib12 dataset (Supplemental Figure \[fig:fit\]).

We note that a separate publication is in progress (Teske et al. in prep) that will discuss the reliability of FGK dwarf star abundances produced by the APOGEE automated analysis pipeline [ASPCAP; @Garc16; Holtzmann et al. in prep, Jonsson et al, in prep]. Initial results (also discussed in Wilson et al. in prep) suggest that, for solar-type stars, the Fe, Mg, and Si abundances produced by ASPCAP are reliable at the $\sim$0.15 dex level. The ASPCAP Na abundances appear to be less reliable, upon comparison with a small sample of values derived from optical data. For consistency, we did not modify the DR13 APOGEE Na abundances to bring them into better agreement with the optical data. We note that Figure 1 shows that the @Adib12 and the APOGEE samples have similar ranges in Na abundances.

Methods Summary
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### Planet Composition Model

There is extensive debate as to the exact nature of the Earth’s composition, from one closer to a volatilized carbonaceous chondrite [@McD95; @McD03], to 