  Currently popular ideas about the Earth's interior have developed almost
entirely on the basis of physics. In the spirit of the United Nations'
designation of 2011 as the International Year of Chemistry, I unify chemical
and physical inferences for Earth-matter below the depth of 660 km. I relate by
fundamental mass ratio relationships the internal parts of that region with
corresponding enstatite chondrite parts, providing a quantitative basis for
understanding the "seismically rough" matter at the core mantle boundary, D'',
as arising from Earth-core precipitates, the "core-floaters", CaS and MgS. I
suggest that the ultra-low velocity zone consists of CaS.
