Xenon Isotopes in Mid Ocean Ridge and Ocean Island Basalts: Implications for the Volatile Evolution of the Earth

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"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."The Iodine-Xenon and Plutonium-Uranium-Xenon radioactive decay systems are the only ones that can provide constraints on the timing and rates of degassing from the Earth's mantle during the first couple hundred million years of the Earth's history. Dissecting the timescale of mantle degassing is important for understanding the compositions of the major gases that were present in the Earth's early atmosphere. For example, if most of the degassing of the Earth's mantle is accomplished before the mantle gets oxidized, particularly prior to the formation of the Earth's core, the early atmosphere would have a reducing composition (Hydrogen, Carbon Monoxide, Methane). On the other hand, a more delayed degassing would have led to a neutral or slightly oxidizing atmosphere (Carbon Dioxide, Water, Nitrogen). Understanding which of these two scenarios is most probable would have great implications for the state of the pre-biotic chemistry on the Earth's surface.Recent technical advances in the Noble Gas Laboratory at Harvard now make it possible to detect small isotopic anomalies in Xenon in mantle derived basalts. Therefore, a suite of heavy noble gas measurements (Neon, Argon, Krypton, Xenon) in basalts from mid-ocean ridges in the Atlantic, Pacific, and Indian Ocean, along with basalt samples from hotspots such as Hawaii and Iceland is proposed. In particular, the research will address whether there are variations in Plutonium/Iodine ratios within the mantle and whether the Xenon and Argon compositions of the upper mantle resembles the Sun, chondritic meteorites, or air. The results obtained from the proposed research would provide new information on sources of volatiles to planet Earth, the timing of degassing of the Earth's mantle, and the volatile evolution of planet Earth.