From here on I’ll focus exclusively on siderophile elements in the silicate Earth, and try to ignore elusive, imaginary friends, such as the BSE, that represent model compositions. The largest mantle domain that we have more or less direct access to is the DMM, so it is a good place to begin. The DMM comprises most of the upper mantle, and chemically may extend well into the lower mantle (e.g., Workman and Hart, 2005; Arevalo et al., 2013). We have indirect access to it in the form of MORB, and may have direct access to...

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