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Project Progress

Coupled model of the anaerobic, early Archean biosphere, prior to the origin of oxygenic photosynthesis (Kharecha, Kasting, and Siefert). This model includes organisms that metabolize using H₂, H₂S, and Fe⁺⁺ as reductants. A primary goal was to estimate the production rate of methane. For reasonable assumptions about hydrogen outgassing and escape rates, CH₄ production should have been within a factor of 3 of the modern value, ~500 Tg CH₄/yr. In the low-O₂ Archean atmosphere, this would have been enough to produce CH₄ concentrations of 1000 ppmv, or higher. Such CH₄ concentrations could have helped to keep the climate warm despite reduced solar luminosity at that time.

Horizontal gene transfer (HGT) and its effect on genome coalescence (Siefert). The effect of HGT on cyanobacterial genomes and the Bacilliaceae lineage has been examined using a bioinformatics approach. It is found that genes can be defined that are both unique and less likely to be transferred in each lineage of bacteria.

Analysis of life in aquifers and hyperalkaline (pH > 11) dilute (<100 ppm total dissolved solids) springs associated with terrestrial serpentinizing bodies ( Rye, Johnson). We are characterizing the microbial community structure at the Cedars site, California. Analysis of data from DGGE experiments has yielded a preliminary tree of roughly 20 novel organisms. Media development has now allowed us to isolate a number of pure cultures, all of which map within the Betaproteobacteria. This site continues to serve as a model system for the simulation of life at the surface of young terrestrial bodies.

Photosynthetically active radiation and light-harvesting photosynthetic pigments on Earth-like planets around F, K, and M stars (Kiang, Segura, Siefert, Tinetti, Cohen, Meadows). A paper is soon to be submitted on our extensive survey of Earth’s photosynthetic organisms, comparing their metabolisms, pigments, reflectance spectra, and environmental niches. We have identified strong candidate wavelengths of photosynthetic pigment light absorption for organisms evolved on Earth-like planets orbiting F, K, and M stars with different atmospheric compositions (Figure 1), thus defining potential alternative biosignatures for remote detection.

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