Investigating the syngeneity and paleobiology of hydrocarbon biomarkers in the Fortescue Group at 2.7-2.8 Ga

The oxygenation of the Earth's atmosphere was of great importance because it dramatically altered the evolutionary paths of organisms. It is widely accepted that the oxygenation of the previously anaerobic Earth was initiated by the oxygenic photosynthesis of cyanobacteria. However, our understanding of the key steps and timing of oxygenation is still limited. The presence of cyanobacteria at least as early as 2.7 Ga has been suggested by the presence of 2-methylhopanes, diagnostic biomarkers for cyanobacteria. This is well before the Great Oxidation Event at 2.4 Ga, when atmospheric free oxygen first appeared in appreciable quantities on the Earth. However, some researchers have rebutted this evidence, by demonstrating that some of the biomarkers are contaminants. The purpose of our research is to critically assess the evidence for cyanobacteria at 2.7-2.8 Ga by focusing on the record preserved in the Fortescue Group of the Pilbara region in Western Australia. The Fortescue Group crops out over a large area and drill core of the group is also available. The rocks are of a very low metamorphic grade (prehnite-pumpellyite facies), and they contain microfossils, abundant stromatolites, and hydrocarbon biomarkers. Extraction of hydrocarbons is being performed on carbonates and cher ts containing stromatolites, and early results will be reported.1 page(s