Our paper describing how highly siderophile elements such as platinum, palladium, rubidium and iridium were removed from Earth's mantle and segregated into the core was published online and will be in the September 9, 2016 issue of Science. Here is a link to the publication in Science.
A one-paragraph summary:
It shows evidence that heavy elements called highly siderophile elements like platinum left the rocky part of Earth into the core as the rocky part of the Earth crystallized from molten magma into solid rock. This is very different than what most experts thought before. The previous hypothesis was that these elements sank to the core with iron during core formation itself, but when we tested this idea with laboratory and numerical experiments, it didn't work. Instead, we had to revive a poorly promoted hypothesis from 1991 called the Hadean Matte. During the Hadean Matte, as the rocks crystallize, there are too many sulfur atoms to fit in the silicate crystal lattices. This sulfur grabs iron atoms to make iron-sulfide and then sink to the core, but as they do so they also grab highly siderophile elements such as platinum, palladium, rubidium, iridium etc. This hypothesis passed all of our tests that the previous model failed.
We tested both hypotheses via a numerical model that simulates the growth and differentiation of Earth. During core formation events, we determined what quantity of HSEs would be segregated into the core according to partitioning models created from laboratory experiments done at high pressures and temperatures. Similarly, for the iron sulfide segregation model, we conducted appropriate experiments to determine how much HSE segregation occured during those events.