This project aims to directly constrain the melting history and composition of the mantle of the Earthfor the first 750 Ma of its history. So far, our limited knowledge hinges on isolated detrital zircons fromArchean crustal rocks. They indicate crustal extraction as early as 4.4 Ga with peaks at 4.0 and 4.3 Ga butreveal conflicting models for the composition of the Hadean mantle. Both the timing and extent of theseearly crust formation events and the composition of the Hadean mantle have crucial implications for ourunderstanding of the Early Earth’s chemical evolution and dynamics as well as crustal growth and thermalcooling models. Sulfides (BMS) and platinum group minerals (PGM) may hold the key to these fundamentalissues, as they are robust time capsules able to preserve the melting record of their mantle source overseveral billion years.I propose to perform state-of-the-art in-situ Pt-Re-Os isotopic measurements on an extensivecollection of micrometric BMS and PGM from Archean cratonic peridotites and chromite deposits, andpaleoplacers in Archean sedimentary basins. For the first time, < 20 μm minerals will be investigated for Pt-Re-Os. The challenging but high-resolution micro-drilling technique will be developed for in-situ samplingof the PGM and BMS with subsequent high-precision 187Os-186Os isotopic measurements by NTIMS. Thishighly innovative project will be the first to constrain Hadean Earth history from the perspective of theEarth’s mantle. By opening a new window towards high-precision geochemical exploration for micrometricminerals, this project will have long-term implications for the understanding of the micro to nano-scaleheterogeneity of isotopic signatures in the Earth’s mantle and in extra-terrestrial materials.