Biogenicity of silicified microbes from a hydrothermal system: relevance to the search for evidence of life on earth and other planets

Scanning electron microscopy and microprobe analysis have been used to examine microstructures recovered from a hydrothermal mound at the Trans-Atlantic Geotraverse. Our analyses of hydrothermally precipitated Fe-rich cherts shows strong evidence for silicified microorganisms at depths of less than 1 m. The criteria for biogenicity are morphological similarities to living bacteria and an elevated carbon and nitrogen content with an N/C ratio consistent with marine microbes. The absence of calcium means they can not be confused with abiological carbonate or sulfate artifacts. As a modern analog of Archean hydrothermal sites, our results are informative about the mode of microbial preservation, and because of the shallow extraction and proximity to distinctive topographical features, investigation of hydrothermal sites should optimize future explorations for detecting past or present life on the surface of Earth and other planets.