Recent observations from Mars orbiter and rover missions provide unambiguous evidence for opaline silica (SiO2*H2O) in various settings on the Martian surface. In the case of opaline silica outcrops and soil identified by the Spirit rover in the Columbia Hills of Gusev crater, a suite of geologic features demonstrates that these materials are the products of a volcanic hydrothermal system. But the nodular expression of many of the outcrops and sub-cm-scale “digitate protrusions” they contain remained enigmatic. Now, remarkably similar features have been observed in small discharge channels emanating from hot springs and geysers in a high elevation geothermal field known as El Tatio in the Atacama Desert of northern Chile. The micro-digitate silica structures at El Tatio are possible microstromatolites, features that arise through microbial mediation of silica precipitation. By analogy, the comparable features on Mars are potential biosignatures.
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