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Project Progress

Research continued in the following six areas: late Archean — early Paleoproterozoic hydrocarbon biomarker molecules, early Archean sulfur isotopes, metamorphism of early Archean biosignatures, nutrient availability (N, P) in Archean oceans, geochronology of a late Archean flood basalt province, and diamond drilling of astrobiologically significant Archean and early Proterozoic sedimentary horizons in the Pilbara Craton of Australia. Field-work was conducted on early Archean supracrustal rocks of the Warrawoona and Coonterunah Groups in the Pilbara Craton, Australia . Principal outcomes were:

• Publication of complete results on hydrocarbon biomarker molecules in late Archean and early Paleoproterozoic sediments, showing that cyanobacterial and eukaryotic geolipids were present in rocks half a billion years before other fossils of these groups appear in the geologic record, and that molecular fossils can survive for much longer under high-temperature regimes than previously expected.
• A thorough review of the Archean sulfur cycle and constraints upon sulfur isotopic fractionation confirmed the existence of microbial dissimilatory sulfate reduction in ~3.5-billion-year-old oceans, establishing that complex metabolic pathways and peripherally branching bacterial phyla had already evolved.
• Analysis of carbon isotopes in 3.52-billion-year-old sedimentary rocks show that, despite low-grade metamorphism (greenschist facies), isotopic fractionations resembling those imparted by Calvin-Benson cycle Rubisco autotrophy and by methanogenesis, survive in carbonates and cherts.
• U-Pb dating of zircons in felsic tuffs and volcanics interbedded with late Archean flood basalts constrained the age of the oldest-known reversal of the Earth’s magnetic field and allowed calculation of continental drift rates, implying very rapid horizontal tectonic processes on the early Earth.
• Planned deep diamond drill coring of three well-preserved sedimentary intervals (Hamersley-Fortescue, Warrawoona-Coonterunah, and Tumbiana) in the Archean Pilbara Craton will test syngenicity of hydrocarbon biomarkers and provide unweathered geochemical samples for redox-sensitive environmental indicators.

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