This proposal aims to constrain the late accretion history of the Earth and the differentiation of the earliest silicate reservoirs in planets. Highly siderophile elements (HSE) constrain the late accretion of material onto the Earth; a process that potentially delivered water to Earth. During core formation, HSE strongly partition into metal. Once core formation ceases, newly accreted HSE-rich material will significantly contribute to the HSE budget of the Earth’s mantle. The HSE are more abundant in the Earth’s mantle than predicted from low temperature partitioning experiments and feature nearly chondritic relative abundances. This implies a significant late accretion of chondritic material (“the late veneer”). This idea is challenged by high pressure/temperature experiments indicating that the HSE were left in the behind in the mantle during core formation, thereby calling into question the late veneer. To address this issue, I propose the setup of new isotopic tracers and utilize (i) nucleosynthetic anomalies and (ii) stable isotope systematics of the HSE to determine the origin of HSE in the Earth’s mantle. Unravelling this issue is a major advance in understanding planetary accretion. Formation of the earliest silicate reservoirs probably occurred contemporary to late accretion. Global differentiation in terrestrial silicate reservoirs may have taken place within the first 30 million years of the Earth’s formation based on Sm-Nd isotope data. This timing has been debated on various grounds. The 92Nb-92Zr decay system is a potentially powerful chronometer to further constrain this issue. Its usefulness, however, has been hindered by uncertainties of the initial 92Nb abundance in the solar system. I propose to obtain unequivocal evidence from old differentiated meteorites to settle this debate. The results will have implications for understanding early silicate differentiation on asteroids and - depending on the initial 92Nb abundance - the Earth and Mars.
Field of science
- /natural sciences/physical sciences/astronomy/planetary science/planets
- /natural sciences/physical sciences/astronomy/planetary science/asteroids
- /natural sciences/physical sciences/astronomy/planetary science/meteorites
Call for proposal
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