Copper isotopes and the role of sulphides during Earth’s differentiation

Comparison of the chemical composition of primitive meteorites, thought to represent Earth’s building blocks, to that of Earth’s mantle can constrain the processes that took place during the differentiation of our planet. Major events such as volatile depletion and core formation affect the mantle abundances of elements such as copper. High precision copper isotope analysis of meteorite and terrestrial samples, coupled with experimental data, indicates that neither volatile loss nor metal-silicate equilibration can explain the isotopically heavy copper composition of Earth’s mantle. Instead, a sulfide-rich phase which segregated from the silicate Earth explains this signature; we propose that a Fe-O-S liquid formed during the final stage of magma ocean crystallization and ponded to the base of the mantle, and may have subsequently entered the core.