Biosignatures in fossil sinters: implications for astrobiology strategies

The search for life on Mars has been guided by the search for biosignatures in the geologic record of Mars and of Martian analogues on Earth. Siliceous hot springs are key astrobiological targets as they provide ideal conditions for biogenesis and may have fossil counterparts, termed silica sinters, on Mars. This study aims to (i) qualitatively assess the biogenicity of Holocene to Miocene sinters from New Zealand based on morphological biosignatures, organic biomolecules, and trace element fractionation patters, and (ii) provide insights into quantitative frameworks for biogenic assessments using Bayesian statistics. Results show that bacterial biomarkers have been detected in all samples, even of Miocene age, and that Post-Archean average Australian Shale-normalised rare earth elements patterns may help discriminate between biotic and abiotically precipitated sinters. The sensitivity analysis of a Bayesian framework shows that detecting more than seven biosignatures does not increase the reliability of biogenic assessments, unless their probability of being false positives is well constrained. This study provides a starting point for systematic biogenic assessments of fossil silica sinters, and emphasizes the need for quantitative support of these assessments and of astrobiology strategies in general.