The composition of Earth's early atmosphere strongly influenced chemical reactions that occurred on our planet's surface. While outgassing of the early Earth's interior, such as through a magma ocean, leads to an oxidized H2O-CO2 atmosphere, if the early atmosphere was largely derived from late accreting planetesimals, then the oxidation state of the impactor controls the composition of the atmospheric gases. The proposed noble gas measurements will be ideally suited to address whether the early atmosphere was produced through outgassing of the mantle or impact outgassing of late accreting planetesimals. In addition to the origin of the early atmosphere, the noble gas measurements will provided new constraints on what sources contributed volatiles to Earth and at what stage of Earth's accretion the volatiles currently in the solid Earth were delivered.
Specifically, Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr) and Xenon (Xe) isotopic measurements will be made on mid-ocean ridge and ocean island basalts. These noble gas measurements will help to answer the following key questions: i) are the stable isotopic compositions of Xenon and Krypton in Mid-Ocean Ridge Basalts (MORB) and plume source(s) solar, chondritic, or air-like? ii) are the elemental abundance ratios observed in Iceland basalts representative of other mantle plumes? iii) are the observations of higher Pu- to U-derived fission Xe and lower I/Pu ratio for the Iceland plume representative of other mantle plumes? iv) is the magnitude of 129Xe/130Xe isotopic anomalies in MORBs and plume source(s) constant or is there variability in the ratio associated with subduction of air/seawater? and v) what is the degree of mixing between the MORB and plume source over 4.45 Ga such that differences in Xenon isotopic compositions can be preserved in the present day mantle? Answers to these questions will address the broader goal of understanding the origin of the early atmosphere and the timing and processes controlling the acquisition of terrestrial volatiles.
