Biology
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmep21a0739w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #EP21A-0739
Biology
[5200] Planetary Sciences: Astrobiology, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The surface of modern Mars is rich in S and Fe minerals. Variations in water activity and the weathering reactions of these minerals have been integral to developing Martian surface conditions during the last 2 Ga. Terrestrial gossans, especially those formed from acid-saline solutions at low water-rock ratio, provide an important analog for understanding how S and Fe minerals may have weathered on Mars. Acidophiles and chemolithotrophs have been identified in these environments on Earth, so they also comprise a model system for putative biosignature formation and preservation that is relevant to conditions on early Mars. The Iron Mountain massive sulfide deposit is capped by a gossan, parts of which were exposed at the surface prior to mining, and parts of which have been exposed for several decades. The deposit is located in seasonally dry northern CA with high late spring to early fall evaporation rates. Samples of pyrite, iron-oxide-rich, and sulfate-rich gossan were collected during the dry season in late spring 2010. Mineral species identified with SEM-EDS, XRD, and optical microscopy include: pyrite, goethite, lepitocrocite, hematite, schwartmanite, gypsum, quartz, and acanthite. As yet unidentified soluble sulfate minerals formed by evaporative concentration are also present. Distilled water added to a pyrite-sulfate sample yielded a pH of ~2.5 once the evaporites dissolved. The spatial variability of minerals and the extent of alteration provide the opportunity to study weathering gradients and solution/reprecipitation in this system. Putative microbial communities containing filaments have been observed in small patches on sample surfaces and in fractures with FEG-SEM and optical microscopy. Although present, textural features interpreted to have formed microbially are sparse. The relative paucity of microbial morphologies in this analog acid-saline system combined with their heterogeneous spatial distribution presents a challenge for remote detection by a rover. In addition, long-term preservation of organics in the oxidizing environments indicated by the presence of iron oxides is difficult. Thus, poor preservation of organic biomarkers might be expected even if microbial colonization of the Fe-rich substrate was present on Mars. However, if microbial activity influences local mineralogy or mineral morphology, this may provide evidence for microbial activity even in the absence of chemical biosignatures.
Sumner Dawn Y.
Williams Albert J.
Zierenberg Robert A.
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