Biosignature Preservation in Subsurface Serpentinizing Systems

Abstract:

With the launch of NASA’s Perseverance Rover, interest has grown toward understanding how evidence of ancient microbial life might be detected on Mars. Among its goals, the rover will "[a]ssess the biosignature preservation potential within the selected geological environment and search for potential biosignatures"[1]. Attention has thus been drawn toward novel Mars-analog microbial habitats on Earth and taphonomic processes that can lead to the capture and preservation of evidence of life over geological timescales.

One such novel environment is among active serpentinizing and serpentine-bearing systems, the latter of which has been identified throughout Mars’ surface [2, 3] and potentially within the Perseverance rover landing site [4]. Serpentinization is a geological process involving the interaction of water and ultramafic rock, the chemical byproducts of which may serve as an energy source for chemolithotrophic microbial communities.

In the presence of dissolved CO₂, serpentinization results in the precipitation of carbonate minerals such as magnesite, calcite, and dolomite. Notably, this process can cause an increase of the solid rock volume and associated pressurization conditions that may lead to fracturing of the host rock [5, 6]. Fractures formed by this process, in addition to those created by tectonic processes, can function as conduits for water transport and may serve as habitable niche environments. As serpentinization proceeds along these fractures, so can the precipitation of carbonates, which eventually results in fractures becoming completely sealed by carbonate minerals.

In the present study, we explore whether the precipitation of carbonate minerals within such fractures can serve as unique taphonomic windows to preserve evidence of subsurface microbial communities for geologic timescales. Here we report the detection of fossilized communities within drill core samples of serpentine-hosted carbonate veins from the Samail Ophiolite in Oman.

[1] Mustard et al. (2013) MEPAG 150 (2013): 1-154 [2] Ehlmann et al. (2010) JGR 37 L06201; [3] Amador et al. (2018) Icarus 311 113-134 [4] Dobrea and Clark (2019) LPSC 2019 id.1249 [5] Iyer et al. (2008) Earth and Planetary Sci. Let.267 503-516 [6] Kelemen and Matter (2008) PNAS 45 17295-17300