| To understand the potential for recovering biosignatures in ancient Mn deposits, the modern microorganisms, Bacillus subtilis and Escherichia coli, were exposed to different concentrations of Mn(II), and the longevity of their DNA and lipids was monitored over time. Over the 180 days of the experiment, DNA was observed to degrade, and was estimated to have a longevity of only about a year. B. subtilis and E. coli were exposed to different concentrations of SiO2 as a comparison to Mn(II) for the DNA studies. Exposure to SiO2 provided conditions in which the DNA had a greater longevity when compared with exposure to Mn(II), but was estimated to degrade within only a few years. Results of the degradation of phospholipids (analyzed as FAMEs), free fatty acids, and hydrocarbons was variable over time. Variability was observed at the start of the experiments, and between replicates. In general, although some degradation of these biosignatures was observed, the longevity greatly exceeded that of DNA.;Investigations of potential biosignatures in ancient Mn deposits was conducted on samples collected from the ∼2.0 Ga Kalahari Manganese Field, South Africa. Carbon isotopes, mineralogy, and potential morphological biosignatures were analyzed with the hopes of identifying a biological component to the ores. Analysis of inorganic carbon isotopes revealed a trend in mineralization from the bottom (oldest) to the top (youngest) of the core. Inorganic carbon isotopes ranged from delta13C -15‰ to -3‰ in the Mn and banded iron formation (BIF) ores. Depleted inorganic carbon isotope signatures were observed at the initiation of Mn metallogenesis. Organic carbon isotopes generally ranged from delta13C -23‰ to -28‰, but some BIF samples showed organic carbon isotopes that ranged from delta 13C -24‰ to -34‰. Mineralized microfossils were seen embedded in the background matrix material. These structures, which contained increased carbon when compared with the background, were later confirmed to be contaminants originating in the tap water used to cool the saw. |
