As noted in Chapter 3, chemistries that may have led to life (prebiotic chemistry) include Miller-Urey type atmospheric electric discharges, serpentinization reactions of Fe-Mg minerals (e.g., olivine), Strecker synthesis, Fischer-Tropsch synthesis, and FeS-driven synthesis. The fundamental step in prebiotic chemistry is the formation of compounds with C-C bonds from single carbon molecules (e.g., CO, CO2, CH4). Therefore, the best sites to search for clues about prebiotic chemistry would be those where organic carbon is most likely to be preserved. However, as discussed below, no rich deposits of inorganic carbon have been identified on Mars.
The next section describes those sites that may be the best targets to search for biosignatures of past life, including organic carbon. The proposed target mineralogies and lithologies, which include putative hydrothermal systems, evaporites, sediments, iron oxides, and clay minerals, are the best targets to find possible evidence of
FIGURE 4.1 This delicate fan shape is the product of the long-term distribution of sediments by flowing liquid water. Image from the Mars Orbiter Camera on the Mars Global Surveyor spacecraft courtesy of NASA/JPL/Malin Space Science Systems. The image covers an area of approximately 8 by 22 km.
prebiotic chemistries. Of these potential sites to preserve biosignatures, the most likely sites are sediments, evapo-rites, and hydrothermal systems based upon observations of terrestrial rock systems.
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