After having done numerous analyses of lunar samples and after having attempted to estimate the bulk composition of the Moon, we wanted to apply our analytical procedures to terrestrial rocks and estimate the bulk composition of the Earth in a similar way as for the Moon. People had complained that high quality chemical and isotopic data of lunar rocks were not available for terrestrial rocks, in particular the concentrations of rare trace elements that were reasonably well known for many lunar rocks were uncertain for samples from the Earth. For example, we had at the time a pretty good idea...

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