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Project Progress

This project focuses on the role of water-rock reactions in mediating the chemistry of early Earth’s surface environment. We are focusing on two lines of investigation: 1) experimental and theoretical studies of organic synthesis by hot fluids reacting with olivine-rich rocks, and 2) field studies of 3.8 billion-year-old terrestrial rocks that may host chemical evidence for life.

The first sub-project involves the Ph.D. thesis of George (Codi) Lazar. Initial studies focus on characterizing the yield of dissolved, simple organic molecules from hydrothermal alteration of ultramafic rocks. A key insight has been realization that the prevalence of this rock type in the Hadean Earth suggests that, in addition to the widely recognized hot spring environments, many other metamorphic settings could additionally produce significant dissolved organics. Preliminary theoretical work revealed that silica content plays a key role in generating the conditions needed for high methane yields. Early results have been reported by Lazar and Manning (2005, 2006). Based on the preliminary theoretical studies, Lazar is conducting experimental studies in a new collaboration with T. McCollum (U Colorado) in Summer, 2006.

The second sub-project was completed in 2006 with the publication of a paper on the geology, age, and origin of a sequence of rocks notable for their great age and possible presence of chemical evidence for life, on Akilia Island, Greenland (Manning et al., 2006). Our new mapping, geochronology, and geochemistry support a ≥3825±6 Ma age for the sequence and a chemical sedimentary origin for Fe-rich quartz-pyroxene gneisses. Quartz-pyroxene rocks on Akilia have been interpreted as metamorphosed chemical sediments that may preserve carbon-isotope evidence for life at the time of their formation. An alternative proposal is an origin by metasomatic alteration. Our results indicate that these rocks experienced a history of deformation and zircon growth identical to other lithologies of the supracrustal body. Metamorphic zircons give a minimum ²⁰⁷Pb/²⁰⁶Pb age of 3589±13 Ma regardless of origin. The two models of formation of quartz-pyroxene rocks were evaluated using field, petrologic and geochemical tests. The distribution of the units, the absence of field or petrologic indicators of metasomatism, and geochemistry (O and Fe stable isotopes, immobile elements and REE) together support a sedimentary, but not a metasomatic, origin. Because their protolith was sedimentary, the quartz-pyroxene rocks are a primary part of the supracrustal sequence and have the same minimum age. Despite strong deformation and polymetamorphism, the Akilia supracrustal enclave contains information about terrestrial surficial processes at ≥3819 Ma.