Determination of Geochemical Bio-Signatures in Mars-Like Basaltic Environments

Abstract

Bio-signatures play a central role in determining whether life existed on early Mars. Using a terrestrial basalt as a compositional analog for the martian surface, we applied a combination of experimental microbiology and thermochemical modeling techniques to identify potential geochemical bio-signatures for life on early Mars. Laboratory experiments were used to determine the short-term effects of biota on the dissolution of terrestrial basalt, and the formation of secondary alteration minerals. The chemoorganoheterotrophic bacterium, Burkholderia sp. strain B_33, was grown in a minimal growth medium with and without terrestrial basalt as the sole nutrient source. No growth was detected in the absence of the basalt. In the presence of basalt, during exponential growth, the pH decreased rapidly from pH 7.0 to 3.6 and then gradually increased to a steady-state of equilibrium of between 6.8 and 7.1. Microbial growth coincided with an increase in key elements in the growth medium (Si, K, Ca, Mg, and Fe). Experimental results were compared with theoretical thermochemical modeling to predict growth of secondary alteration minerals, which can be used as bio-signatures, over a geological timescale. We thermochemically modeled the dissolution of the basalt (in the absence of biota) in very dilute brine at 25°C, 1 bar; the pH was buffered by the mineral dissolution and precipitation reactions. Preliminary results suggested that at the water to rock ratio of 1 × 107, zeolite, hematite, chlorite, kaolinite, and apatite formed abiotically. The biotic weathering processes were modeled by varying the pH conditions within the model to adjust for biologic influence. The results suggested that, for a basaltic system, the microbially-mediated dissolution of basalt would result in “simpler” secondary alteration, consisting of Fe-hydroxide and kaolinite, under conditions where the abiotic system would also form chlorite. The results from this study demonstrate that, by using laboratory-based experiments and thermochemical modeling, it is possible to identify secondary alteration minerals that could potentially be used to distinguish between abiotic and biotic weathering processes on early Mars. This work will contribute to the interpretation of data from past, present, and future life detection missions to Mars.

Early diagenesis at and below Vera Rubin ridge, Gale crater, Mars

“…For an in‐depth discussion, how model and experimental W/R ratios compare, see Olsson‐Francis et al. (2017). CHIM‐XPT calculates the equilibrium reaction of the fluid with the precipitating phases at an overall chemistry of the system.…”

Insights into the Geomicrobiology of Biovermiculations from Rock Billet Incubation Experiments

“…If we can detect small and large-scale biopatterns at lower cost with robotic first-line reconnaissance missions, biopatterns—these hopefully unique or at least characteristic morphological biosignatures—should indicate areas suitable for deeper investigation to search for bioassemblages and other biomarkers indicating extinct or extant microbial life. Attention must be paid to the potential for false positives to distinguish potential biotic from abiotic processes (e.g., [ 22 , 72 ]). Thus, future work must rigorously continue to attempt to distinguish between patterns produced with the mediation of biological processes versus any similar patterns that can be demonstrably attributed to abiotic processes.…”

Biogenic Metal Nanoparticles: A New Approach to Detect Life on Mars?

“…If life ever existed or still exists on Mars, it was or is probably microbial, free-living in fluids or as biofilms in sediments, and probably with carbon-based origins developed in the presence of water, similar to the first life forms on Earth [52]. Such microbial biomass, regardless of their physiological characteristics, might still be preserved in Martian sedimentary rocks or fluids [46,53], or any biological molecules might be trapped in mineralized cells [47]. It is known that the subsurface of Mars has mostly acted as a giant freezer, potentially preserving any remains of Martian life [54].…”

“…The current surface of Mars is exposed to multiple extremes and seen as inhospitable and uninhabitable [45]. These include low temperatures, low pressure, very dry and oxidized conditions, and high levels of ultraviolet (UV) and ionizing radiation exposure, all of which are due to the very sparse Martian atmosphere [45,46].…”

“…When searching for extraterrestrial life on Mars and elsewhere, it is of uttermost importance to define what constitutes a biosignature (evidence of biological processes), and how it relates and differs from "abiosignatures"/abiotic features (derived from non-living ones), particularly to avoid misidentification or wrongful detection [46,47]. One should note that life evades definition and is remarkably complex from a conceptual perspective, which might hamper a clear-cut separation between biotic and abiotic.…”