4:00 PM - 4:15 PM
[MIS02-07] The role of ferrous saponite in the formation of sulfur-bearing organic matter, carbon cycles, and climate on early Mars
Keywords:Early Mars, Organic matter
In-situ CO2 fixation is a key process governing the formation of organic matter, climate stability, and possibly the origin of life on Earth. Exploring the characteristics of organic matter resulting from these in-situ reactions in different planetary environments is essential to identify potential biomarkers for current space missions and to aid in the Astrobiology initiatives of missions in the future.
NASA’s Curiosity rover has investigated the mineralogical and geochemical compositions of lacustrine sediments deposited within Gale Crater on Mars. These analyses tell us information about the geochemistry of early Mars. The SAM (The Sample Analysis at Mars) instrument onboard Curiosity enables detection of organic matter evolved through pyrolysis of drilled samples. Based on mass spectroscopic data acquired by SAM the existence of sulfur-bearing organic matter, including thiols and thiophenes was reported from drilled lacustrine mudstones (Eigenbrode et al., 2018). Terrestrial sulfur-bearing organic matter is known to originate biogenically from metabolism or abiotically through the sulfurization of organic matter in sediments during diagenesis (e.g., Canfield, 2001; Werne et al., 2008). However, few studies, e.g., Heinen & Lauwers, 1996, have investigated the formation of such sulfur-bearing organic matter through CO2 fixation in sulfur-rich surface environments similar to the surface of early Mars. A main reservoir of inorganic carbon on early Mars would be the carbon dioxide atmosphere, suggesting that carbon dioxide fixation was required to form organic matter.
Here, we investigate the formation of sulfur-bearing organic matter through CO2 fixation on sulfur-rich meant to simulate early Mars. Our experiments focus on water-rock interactions between ferrous iron-bearing minerals and an aqueous solution of carbon dioxide and hydrogen sulfide. We conducted systematic laboratory experiments using four types of ferrous iron-bearing minerals: troilite, iron-nickel alloy, magnetite, and ferrous saponite. Among them, ferrous saponite is suggested to be widespread on early Mars (Michalski et al., 2015; Chemtob et al., 2017). However, the effective reducing power of ferrous saponite is uninvestigated because of its instability under oxidizing terrestrial conditions. Each mineral powder was enclosed in glass vials with sodium bicarbonate solution, carbon dioxide gas, and hydrogen sulfide under anoxic conditions, followed by heating at 90°C for 2–4 weeks. After heating, we analyzed the gas compounds using gas chromatography mass spectrometry. [SEM1] .
We found significant production of methanethiol and ethanethiol only in the experiments with iron-nickel alloy and ferrous saponite. The results of Scanning transmission X-ray microscopy analysis of ferrous saponite after the experiments show the presence of aliphatic and carboxyl compounds on the surface or within the interlayers of the saponites. The formation of hydrogen molecules occurs only in the experiments with ferrous saponite and troilite at an order of magnitude higher concentrations than the control experiments without hydrogen sulfide.
These results suggest the possibility that atmospheric carbon dioxide could have been reduced to sulfur-bearing organic matter with the presence of ferrous saponite in aqueous environments on early Mars. Given the widespread occurrence of ferrous saponite on early Mars, in-situ CO2 fixation on ferrous saponite would have acted as a sink of atmospheric carbon dioxide. In addition, evolved H2 could have helped to warm the surface due to the greenhouse effect of collision-induced absorption (CIA) (Wordsworth et al., 2017).
NASA’s Curiosity rover has investigated the mineralogical and geochemical compositions of lacustrine sediments deposited within Gale Crater on Mars. These analyses tell us information about the geochemistry of early Mars. The SAM (The Sample Analysis at Mars) instrument onboard Curiosity enables detection of organic matter evolved through pyrolysis of drilled samples. Based on mass spectroscopic data acquired by SAM the existence of sulfur-bearing organic matter, including thiols and thiophenes was reported from drilled lacustrine mudstones (Eigenbrode et al., 2018). Terrestrial sulfur-bearing organic matter is known to originate biogenically from metabolism or abiotically through the sulfurization of organic matter in sediments during diagenesis (e.g., Canfield, 2001; Werne et al., 2008). However, few studies, e.g., Heinen & Lauwers, 1996, have investigated the formation of such sulfur-bearing organic matter through CO2 fixation in sulfur-rich surface environments similar to the surface of early Mars. A main reservoir of inorganic carbon on early Mars would be the carbon dioxide atmosphere, suggesting that carbon dioxide fixation was required to form organic matter.
Here, we investigate the formation of sulfur-bearing organic matter through CO2 fixation on sulfur-rich meant to simulate early Mars. Our experiments focus on water-rock interactions between ferrous iron-bearing minerals and an aqueous solution of carbon dioxide and hydrogen sulfide. We conducted systematic laboratory experiments using four types of ferrous iron-bearing minerals: troilite, iron-nickel alloy, magnetite, and ferrous saponite. Among them, ferrous saponite is suggested to be widespread on early Mars (Michalski et al., 2015; Chemtob et al., 2017). However, the effective reducing power of ferrous saponite is uninvestigated because of its instability under oxidizing terrestrial conditions. Each mineral powder was enclosed in glass vials with sodium bicarbonate solution, carbon dioxide gas, and hydrogen sulfide under anoxic conditions, followed by heating at 90°C for 2–4 weeks. After heating, we analyzed the gas compounds using gas chromatography mass spectrometry. [SEM1] .
We found significant production of methanethiol and ethanethiol only in the experiments with iron-nickel alloy and ferrous saponite. The results of Scanning transmission X-ray microscopy analysis of ferrous saponite after the experiments show the presence of aliphatic and carboxyl compounds on the surface or within the interlayers of the saponites. The formation of hydrogen molecules occurs only in the experiments with ferrous saponite and troilite at an order of magnitude higher concentrations than the control experiments without hydrogen sulfide.
These results suggest the possibility that atmospheric carbon dioxide could have been reduced to sulfur-bearing organic matter with the presence of ferrous saponite in aqueous environments on early Mars. Given the widespread occurrence of ferrous saponite on early Mars, in-situ CO2 fixation on ferrous saponite would have acted as a sink of atmospheric carbon dioxide. In addition, evolved H2 could have helped to warm the surface due to the greenhouse effect of collision-induced absorption (CIA) (Wordsworth et al., 2017).