Program > Browse abstracts by speaker > Siebert Julien

Volatile elements, defined by their condensation temperature (Lodders, 2003), have an uncertain accretion history on Earth. Were they accreted synchronously (Rubie et al., 2015) or after core formation (a.k.a. dry accretion hypothesis) (Albarede, 2009)? Was their delivery continuous throughout Earth's accretion process (Righter and Drake, 1997) or restricted to the later stages (Schönbächler et al., 2010)? Understanding their timing and mechanisms of accretion on Earth may help for understanding planetary habitability.

To address these questions, we consider three moderately siderophile and volatile elements (MSVE): sulfur, selenium and tellurium (S, Se, Te). Planetary processes, like core segregation from an early Earth's magma ocean may explain their similar depletion in the bulk silicate Earth (BSE) with respect to lithophile elements of similar volatility (e.g. zinc) (Wood et al., 2006). While previous studies suggest MSVE were delivered post-core formation (Rose-Weston et al., 2009, Wang and Becker, 2013), their experimental conditions differ significantly from those expected for early Earth's metal-silicate equilibration (Rose-Weston et al., 2009, Siebert et al., 2012), leaving the debate unresolved. Here, we present new experimental results on metal-silicate partitioning of these MSVE under core-mantle equilibration conditions (Siebert et al., 2012), showing similar light elements composition to those expected for Earth's core (Hirose et al., 2021). Thestriking differences with lower pressures and temperatures experiments (Rose-Weston et al., 2009) highlight that BSE compositions can be reproduced without evoking post-core formation volatile delivery. Consequently, if a late veneer existed, its mass must have been minimal and/or composed of largely volatile-depleted material, reshaping our view of Earth's late accretion.