WHERE SHOULD WE LOOK FOR EVIDENCE OF PAST LIFE ON MARS? CLUES FROM GLEN TORRIDON AND VERA RUBIN RIDGE, GALE CRATER, MARS

Organic matter represents an important biosignature which has been shown to record ancient life up to 3.8 billion years old on Earth [1]. This time period also corresponds to a period of potential habitability on Mars [2]. Organic matter has been previously detected in Gale crater, Mars by the MSL Curiosity in both variable concentrations and compositions [3]. The purpose of this project is to test the hypothesis that these variable detections of organic matter can be explained, at least in part, by differences in diagenetic environments.

We are therefore analyzing the geochemical, mineralogical, and optical data of samples from the altered Vera Rubin Ridge (VRR) and Glen Torridon (GT) sites. We chose these locations because GT and VRR are believed to be stratigraphically equivalent, but VRR has likely encountered multiple fluids with different pH, salinity and temperatures during late diagenesis [4], whereas GT has significant detections of organic compounds [5]. The comparison between these two locations therefore allows an examination of the impacts of diagenetic conditions on the preservation of organic matter.

VRR’s mineralogy consists of increased hematite and decreased clay minerals and sulfate relative to GT, and GT consists of an abundance of clay minerals, hematite and minor amounts of magnetite and siderite [4]. Elemental concentrations show a higher Fe/Mn ratio in VRR relative to GT, and higher concentrations of Mn in GT relative to VRR, both of which are consistent with reducing conditions [6]. Analyses of Evolved Gas Analysis data indicate that the three samples Glen Etive, Rockhall, and Marimba have substantially higher H₂ concentrations along with a lower Fe/Mn ratio than other samples. Glen Etive also shows the highest concentration of S-bearing organics detected so far on at Gale crater [5]. This suggests that H₂ and Mn may be good indicators of reduced conditions that may preserve organic matter, with important implications for the search for potential past biosignatures on Mars.

References

[1]Suess, E. (1979) Geochimica Cosmochemica Acta 43, 339-352.

[2]Biemannet al. (1979) JGR, 82, 4641-4658.

[3]Eigenbrode et al. (2018) Science 360, 1096-1101.

[4]Rampe et al. (2020b) JGR, 125, e2019JE006306.

[5]Millan et al. (2021) LPSC, 52, #2548.

[6]Yen et al. (2010) LPSC, 41, #2546.