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Project Progress

Further research was performed on Archean hydrocarbon biomarker geochemistry, sulfur isotopic fractionation, and Paleoproterozoic hydrocarbon preservation in fluid inclusions. New research was initiated in the areas of metamorphism of Archean biosignatures, Archean paleobarometry, and on the age and origin of controversial “microfossils” putatively of Archean age from the Pilbara Craton, Australia. Field-work was conducted on Hadean supracrustal rocks from Isua, Greenland, the early Archean Apex Basalt near Marble Bar, Australia, and the late Archean Fortescue Group near Tom Price, Australia.

Principal outcomes were:

1. Microthermometric analysis of Paleoproterozoic oil-methane-carbon dioxide-water fluid inclusions from ~2.4 billion year old rocks from Elliott Lake, Canada, showed that the hydrocarbons were trapped early at high temperatures and demonstrated the survival of complex hydrocarbon molecules for billions of years under closed-system and high-pressure conditions, thus establishing a base-line for preservation of such biosignatures on other planets.
2. A major study of hydrocarbon biomarker molecules in late Archean sediments from the Hamersley Basin showed that cyanobacterial and eukaryotic lipids are 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 thermal regimes than previously expected.
3. A thorough review of the Archean sulfur cycle and constraints upon sulfur isotopic fractionation confirmed the existence of microbial sulfate reduction in ~3.5 billion year old oceans and showed that peripherally branching bacterial phyla had already evolved.
4. Mapping of a newly discovered outcrop of clastic metasediments ~3.8 billion years old confirmed the existence of turbidites in the Isua greenstone belt and demonstrated the occurrence of large low-strain domains within the world’s oldest supracrustal succession.
5. Mapping of the ~3.5 billion year old Apex Basalt indicated that the “microfossils” previously reported from this unit are not as old as the surrounding rocks.