Volatile elements (e.g. H, C, S) have a fundamental role in planetary evolution. But how and when budgets of volatiles were set in planets and the mechanism of volatile depletion in planetary bodies remains poorly understood and represents a fundamental obstacle in understanding the chemical processing of terrestrial planets. Two main theories exist. Either Earth accreted ‘dry’, with Earth’s building blocks completely devoid of volatile elements. Then, the Earth’s complement of volatile elements was only established later, once the Earth was differentiated into a core and mantle, by the addition of a late veneer. Or, the Earth accreted ‘wet’ where volatiles where present during the main stages of accretion and differentiation of the Earth. The imprint of core formation on the geochemistry of siderophile and volatile elements of the present mantle can discriminate between these two competing scenarios. We will use core formation experiments and the geochemical signatures from metal-silicate equilibration of three siderophile and volatile elements sulfur, selenium, and tellurium. An original and complementary multi-techniques approach combining experiments at high pressure and high temperature, and high-resolution analyses on quenched samples will be developed to obtain new constraints on the origin of volatiles elements on Earth. The objectives of our research program will be divided into three main targets: (1) Determining the S, Se, and Te metal-silicate partitioning at the direct pressure and temperature conditions of a deep magma ocean. These results will be used to test whether the abundances of these elements can be predicted by current models of Earth differentiation involving metal- silicate equilibrium. We will consequently evaluate if the addition of a given type of meteorite component following initial core formation can raise mantle abundances of S, Se, and Te to their current level. (2) Determining the sulfur isotopic fractionation between metal and silicate at high pressure and high temperature. The results will prove whether core–mantle differentiation generated the recently observed non-chondritic 34S/32S ratio of the silicate Earth. This will provide new independent constraints for the budget of sulfur in the core and the volatile accretion history of the Earth. (3) Determining the speciation of sulfur in (Fe, S) alloys at HP-HT for varying sulfur contents. The results will provide a mechanism to drive sulfur isotopic fractionation to the predicted higher 34S/32S ratio in the core than that of chondrites. Experimental methods developed will place this project at the frontier in between experimental!petrology, stable isotopes geochemistry and mineralogy, as within the new scientific objectives of the Institut de Physique du Globe de Paris (IPGP).