Determination of the 176-lutetium Decay Constant in Planetary Materials and Implications for the Lu-Hf Evolution of the Interior of the Earth

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How did the Earth form and what was its initial composition for the lutetium-hafnium radiogenic isotopic system? The 176Lu-176Hf system is widely used in geochemistry as a chronometer and tracer of planetary evolution but the initial conditions for the formation of the Earth remain unclear. Some meteorites are the only witnesses left of the earliest stages of planetary formation (~4.57 billion years ago). The objective of the proposed research is to measure the Lu-Hf isotopic composition of some of the most pristine meteoritic objects of known ages. The proposed work will place tight constraints on the 176Lu decay constant and initial Hf isotopic composition of the building materials of rocky planets. These parameters are extremely important to the geochemical community in the interpretation of the hafnium but also the neodymium isotopic records of Hadean (more than 3.8 billion years old) and Archean (2.5 to 3.8 billion years old) rocks. It is important to understand the processes responsible for how Earth formed and evolved through its history as it influenced how and when the Earth became an active planet in the Solar System. This study will be performed using state-of-the-art mass spectrometric techniques for measuring the Lu-Hf isotopic composition and also the isotopic compositions of other elements of interest for planetary evolution in collaboration with Dr. Maud Boyet's group at the University of Clermont-Ferrand (France). This project will have major implications for the Lu-Hf, and also Sm-Nd, isotopic geochemical studies and understanding the processes and timing for mantle and crust formation on the Earth and other terrestrial planets. It also will make contributions to other fields of research such as mineral physics, geophysics, planetary sciences, and astrophysics.