EXOA5
Session assets
Introduction: Asteroids are primitive bodies formed from the first solids and organic matter (OM) present in the protoplanetary disc. The study of a particular class of meteorites, the carbonaceous chondrites (CC), derived from small, undifferentiated asteroids considered primitive, has demonstrated that some of them have undergone episodes of aqueous alteration. The mineralogical assemblage of the chondrite provides evidence of aqueous alteration. The formation of secondary minerals, such as phyllosilicates, can be observed. These CC can contain up to 4wt% of OM, some of which is in the form of diffuse OM intercalated in the phyllosilicates 1,2. There are many questions surrounding the history of this OM: to what extent has the OM evolved during this alteration within these mineral assemblages? Does this alteration explain the molecular diversity found in these objects today? Did the presence of OM influence the paragenesis obtained at the end of the alteration process? The co-alteration of OM and minerals under hydrothermal conditions represents a complex set of interactions that has received only limited attention in previous research. This study aimed to investigate these questions by experimentally simulating alteration conditions in the laboratory using model organic and mineral materials.
Methods: Experiments have been designed to investigate the chemical and mineralogical evolution of a hypothetical initial chondritic material exposed to hydrothermal conditions simulating asteroidal evolution. The objective of these experiments is to investigate the interactions between OM and minerals, taking into account the initial alteration conditions that integrate OM and primary minerals that may have been accreted within asteroids.
The organic material used in these experiments is hexamethylenetetramine (HMT), chosen as a model for interstellar organic compounds. This molecule (C6H12N4) constitutes about 40wt% of the organic residues recovered in interstellar ice experiments 3. The selected silicates belong to the olivine and feldspar families, as they are considered primary minerals in asteroids and are observed in the least altered chondrites 4. To further increase the mineral complexity of our study, troilite (FeS), an iron sulfide commonly observed in weakly altered meteorites, was also introduced as a model iron mineral 4,5. The experiments consist of different compositions of HMT with minerals for different durations ( 1 to 100 days) under anoxic conditions at 80°C. We experimented the co-evolution of each mineral alone with the HMT and of a mixture of the three minerals in a ratio of 2:1:2 (peridot:troilite:feldspar) with the HMT.
The mineral fraction was analysed by elemental analysis, infrared spectroscopy, electron microscopy and X-ray diffraction analyses. The diversity of organic compounds formed from HMT was characterised by gas chromatography coupled to mass spectrometry (GC-MS) and infrared spectroscopy.
Results and Discussion: For an initial HMT concentration of 30 mM, we observed different decrease over time depending on the presence and nature of minerals. The degradation of HMT was the faster in the presence of troilite with almost 50% of HMT degraded after 1 day. On the contrary, in the presence of feldspar, the lowest HMT consumption was observed even after 100 days. For peridot and the mixture of minerals, the degradation is comparable to that observed in the absence of minerals, although it occurs more rapidly over extended periods (100 days).
We have characterized by GC-MS, a wide range of chemical families produced by the degradation of HMT under hydrothermal conditions. These include carboxylic acids, diols, ester derivatives, cyanides, amides and N-bearing aromatics. We chose to focus on the amides because they dominated in all experiments, especially in the first 10 days and their formation mechanism from HMT degradation can be easily explained. The presence and nature of the minerals have a crucial influence on the formation of amides. While in some cases, the mineral tends to slow down their formation (HMT alone compared to HMT with peridot, feldspar and complex mixture), the presence of troilite clearly favours their synthesis, but only for formamide derivatives. At longer time (100 days), amide abundance is highest with peridot (Figure 1).
The in-situ transformations of minerals also influence the pH conditions and the release of metallic ions. We were able to identify the presence of many organic salts and chelates, which probably altered the reactivity of the system. The primary mineral has indeed undergone partial transformation into secondary phases, including amorphous silicate, phyllosilicates, or oxides (for troilite samples). Under our alteration conditions, primary minerals were transformed into secondary minerals similar to those observed in CCs 4. Nevertheless, the presence of OM has affected the formation and composition of phyllosilicates, especially from peridot. We observed differences in the nature of the phyllosilicates formed, particularly at short alteration times (<10 days). In addition, the formation of secondary phases such as phyllosilicates, can also result in the adsorption of OM, thereby rendering it less available for future reactivity.
Overall, the evolution of the organo-mineral system cannot be reduced to the sum of the two systems. In fact, the two materials interact and evolve altogether during the alteration process. Moreover, the greater the initial diversity of the organo-mineral system (comprising multiple minerals and OM), the more complex it becomes, and novel and unexpected results are obtained in comparison to the binary system. The results of our experiment simulations clearly demonstrated the significant impact that both phases can have on each other. It was observed that a wide range of molecular diversity is formed under aqueous conditions, which depends on the presence and nature of the minerals. Concurrently, the OM influences the formation of secondary mineral phases.
Aknowledgements: We acknowledge support from the Agence Nationale de la Recherche (ANR 22-CE49-0007 284 ORGAMISS – PI V. Vinogradoff). We thank Daniel Ferry with IR measurements at CINAM and Gregory Excoffier (Spectropole of the Fédération des Sciences Chimiques Marseille, Aix Marseille University) for his help with elemental analysis.
References:
(1) Le Guillou et al., Geochimica et Cosmochimica Acta 2014, 131, 368–392. https://doi.org/10.1016/j.gca.2013.11.020.
(2) Le Guillou et al., Geochimica et Cosmochimica Acta 2014, 131, 344–367. https://doi.org/10.1016/j.gca.2013.10.024.
(3) Caro et al., A&A 2003, 412 (1), 121–132. https://doi.org/10.1051/0004-6361:20031408.
(4) Brearley, Meteorites and the early solar system II 2006, 943, 587–624.
(5) Herndon et al., Nature 1975, 253 (5492), 516–518. https://doi.org/10.1038/253516a0.
How to cite: Serra, C., Vinogradoff, V., Grauby, O., Danger, G., and Duvernay, F.: Co-evolution of organic and mineral phases during hydrothermal alteration of a simulated carbonaceous asteroid., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-244, https://doi.org/10.5194/epsc2024-244, 2024.
More than a century has passed since the hypothesis was first proposed that primordial biological molecules could have formed from non-biological material with the input of some form of energy. Great efforts have been made to test possible energy sources in various environments and to determine whether the abiogenesis of biological molecules is possible. Among all the theories, the one involving hydrothermal vents has recently captured particular attention because it is based on the idea that the reduction of CO2 and the initiation of a proto-metabolism could have occurred by exploiting a life-like thermodynamic disequilibrium on mineral structure that shows structural and compositional similarities with some catalytic centre of enzimes.1–3
Hydrothermal Vent are geological formation generated from the upwelling of geothermal fluids into the ocean, there are two main types of HTV: black smokers (acidic ones) and white smokers (alkaline ones). In the Archean era Alkaline Hydrothermal Vent were generated by the reaction between alkaline (pH 10-11), warm and hydrogen rich fluids with the ocean rich in CO2 (acidic 10-11) and metal ions such as Fe, Ni, Zn, Co, Mn; here at the mixing point a mineral barrier precipitate, composed mainly of iron oxide and hydroxide, green rust and iron sulphide. Across this mineral membrane an electrochemical potential difference is generated, because of the disparity in pH and redox species between the inner and outer sides of the vent, this thermodynamic disequilibrium can be dissipated by coupling two opposite reactions: CO2 reduction and H2 oxidation, the two semireaction take place on the opposite sides of the same mineral structure but in two different environments: the first acidic, the second alkaline. 4
Electrochemistry applied to the study of the behaviour of mineral materials from hydrothermal vents is a valuable tool because it allows for a precise investigation of the reactivity of material surfaces and correlates it with their electronic structure. 5
A hydrothermal vent system can be modelled as a short-circuited fuel cell, with a continuous flow of reactants to the electrodes. These electrodes are made of the material that forms the barrier and are located in two different environments: the first electrode functions as a cathode for the reduction of CO2 in an acidic environment, while the second functions as an anode for the oxidation of hydrogen (or other molecules) in an alkaline environment. An electric current is recorded between the two short-circuited electrodes. This coupling of reactions can be represented in an Evans diagram, analogous to a corrosion process.
Figure 1. Evans diagram in various condition
Figure 2. Short circuited fuel cell model of AHTV
In our laboratory, we developed a technique for synthesizing Mackinawite (FeSm) and Violarite (FeNi2S4). The samples have been characterized using spectroscopic, microscopic, and electrochemical methods. Using these materials, we have prepared electrodes for testing. A series of electrolysis experiments have demonstrated that these materials can electrochemically reduce CO2 at negative potentials as -1.2 V, producing formic acid, methanol, and carbon monoxide. The efficiency of this reaction decreases significantly when less extreme potentials are applied.
Figure 3. Production of formic acid and methanol during a potentiostatic electrolysis on Mackinawite or Violarite.
The behaviour of the electrodes was studied by recording Tafel plots (log(I) vs E) and creating an Evans diagram. This diagram illustrates the operational conditions of pH, catalytic material, and reaction environment under which it is possible to couple the CO2 reduction and hydrogen oxidation reactions effectively. Subsequently, the short-circuited fuel cell was constructed, allowing for the measurement of the current flow (which is proportional to the reaction rate and indicates the cell's polarity) and the electric potential at which the coupled reactions occur.
The results indicate that once the short-circuited fuel cell is assembled, in the absence of reactants and without a pH difference between the two compartments, no current is registered, suggesting that no reaction is occurring. However, upon introducing the CO2 and H2 reactants into their respective compartments, a pH gradient (6.5 vs 8.8) is established. Under these conditions, a reaction current is observed, with its direction indicating reduction at the pole containing CO2 and oxidation at the pole with H2. The potential at which this coupling occurs, on the synthesized metal sulphides materials, is -0.03 V vs SHE (@ pH 6.5), a value too positive to promote the CO2 reduction reaction. The limiting factor in this setup is the anodic reaction, so other conditions have been tested for improving the catalytic activity of the anode, changing electrolyte composition and pH, flux of reactant and even the composition of the electrode itself. For example, using platinum as the anode (a material known for its catalytic properties in reactions involving hydrogen), a coupling potential of -0.44 V is observed, a value within the range where the reduction reaction of CO2 at the cathode can occur.
This approach to measurement and interpretation of Alkaline Hydrothermal Vent functioning represents, in our opinion, a groundbreaking development in the field of studies on this topic. The future challenge lies in identifying the optimal operational conditions that accurately simulate the real environment of an alkaline hydrothermal vent on the Archean ocean floor, capable of facilitating a spontaneous reduction reaction of CO2.
References
1.Russell, M. J. Green rust: The simple organizing ‘seed’ of all life? Life vol. 8 Preprint at https://doi.org/10.3390/life8030035 (2018).
2. Branscomb, E. & Russell, M. J. Frankenstein or a Submarine Alkaline Vent: Who is Responsible for Abiogenesis?: Part 2: As life is now, so it must have been in the beginning. BioEssays vol. 40 Preprint at https://doi.org/10.1002/bies.201700182 (2018).
3. Russell, M. J., Nitschke, W. & Branscomb, E. The inevitable journey to being. Philosophical Transactions of the Royal Society B: Biological Sciences 368, (2013).
4. Hudson, R. et al. CO2 reduction driven by a pH gradient. Proc Natl Acad Sci U S A 117, 22873–22879 (2020).
5. Nitschke, W. et al. Aqueous electrochemistry: The toolbox for life’s emergence from redox disequilibria. Electrochemical Science Advances vol. 3 Preprint at https://doi.org/10.1002/elsa.202100192 (2023).
How to cite: Panico, F., Minguzzi, A., Vertova, A., and Russell, M.: A novel electrochemical approach to the CO2 reduction in Alkaline Hydrothermal Vent, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1068, https://doi.org/10.5194/epsc2024-1068, 2024.
Introduction: The search for organic compounds of biological origin in extraterrestrial environments is one of the major objectives of space missions. However, the interpretations of the origins (biological or otherwise) of organic matter in extraterrestrial environments is a highly complex process. The same concern is encountered when probing for the oldest traces of life on Earth. The search for by-products of potential biological activity such as bio-minerals can be an interesting alternative to decipher biological from non-biological organic compounds. Many minerals of biological origin have been identified on present-day Earth, trapping organic compounds of biological origin, used as template for mineralisation [1], [2]. Therefore, it can be assumed that traces of biological activity could have been preserved more efficiently in the form of inorganic phases such as bio-minerals and potentially able to protect and preserve in their crystallographic structure, biological organic compounds.
Nevertheless, numerous studies also demonstrate the possibility of forming abiotic minerals by organo-mineralization (precipitated solely in the presence of organic molecules without any living organisms) [3], [4], [5]. On Earth, carbonate minerals have been widely produced by bio-, organo-mineralization as well as by inorganic mineralization processes throughout geological history. However, both bio- and organo-mineralization processes use organic compounds as nucleation sites for carbonation leading in both cases to organic-rich carbonates with occasionally similar characteristics [6]. Few studies have shown that the nature of organic compounds, including their physico-chemical properties but also their structural form (chirality) lead to the formation of organo-carbonates with various characteristics (e.g., mineralogies, morphologies) [4], [5], [7]. The presence of one or more COO- functional groups on molecules, which can form a weak bond with Ca2+ ions and thus induce carbonation, could have an influence on the properties of organo-carbonates produced.
The aim here is to investigate the formation of organo-carbonates in various environmental conditions and with various chemical compounds to assess the physico-chemical properties of a wide diversity of organo-carbonates. This could give us an insight into the carbonation mechanisms linked to the intrinsic properties of organic compounds, and enable us to study the impact of these organic compounds on the properties of the organo-carbonates. Data acquired on the organo-carbonates produced in this study are also compared with a dataset acquired on numerous abiotic carbonates and bio-carbonates, both natural and laboratory-synthesized [6], [8], with the aim of identifying relevant criteria for distinguishing carbonates according to their mineralization process and identify possible false positives biosignatures.
Methods: Organo-carbonate precipitation was carried out using the ammonium diffusion method, where carbon dioxide and ammonium, derived from the spontaneous decomposition of ammonium carbonate, are gradually dissolved in an aqueous solution containing CaCl2 and amino acids. Experiments took place at room temperature for 20 days, in desiccators filled with silica gel, ammonium carbonate and petri dishes each containing 30 ml of aqueous solution. The organo-carbonates obtained were studied using a wide range of analytical techniques to investigate their physico-chemical properties. Morphologies were assessed by scanning electron microscopy, mineralogies and structural properties by X-ray diffraction and infrared spectroscopy, and thermal stability and organic content by differential thermal analysis and Rock-eval analysis.
Results: Experiments carried out with amino acids (various concentrations, with enantiomeric forms, inert or oxygenated atmospheres) produced organo-carbonates with different physico-chemical properties, such as different mineralogies (i.e., various proportions of carbonate polymorphs: calcite, aragonite, vaterite), morphologies (i.e., rhombohedral, spherical, needle-shaped with smooth or grooved surfaces), organic matter contents and thermal stabilities. These data were compared with results obtained on abiotic and bio-carbonates (~30 samples) acquired with the same instruments and the same analytical methods [6], [8]. Preliminary results obtained from the analysis of 3 organo-carbonates (precipitated with L-glutamine, L-glutamic acid, L-aspartic acid) show a wide diversity of physico-chemical properties. Each organo-carbonate samples have various proportions of carbonate polymorphs depending on amino acids, different morphologies (Fig. 1 - A, B, C) and a thermal decomposition at high temperatures (~815-820°C) closer to abiotic carbonates than to natural and laboratory-synthesized bio-carbonates (Fig. 1 - D).
Discussion: Based on the preliminary results acquired on few organo-carbonates, minerals can have various morphologies and surface textures occasionally similar to bio-carbonates (spherical or needle-shaped) or abiotic carbonates (rhombohedral). It is therefore undeniable that morphology cannot be the only criterion for distinguishing carbonates according to their mineralization process. However, the spherical shape of some organo-carbonates could be a characteristic linked to the nature of the organic compound used as an organic template for mineralization. According to the physico-chemical properties of organic compounds more or less weak bonds between the Ca2+ and, for example, the COO- groups of certain amino acids might have been formed. Whereas, on the contrary, rhombohedral shapes may imply a limited use of certain organic compounds as triggers for the carbonation. To conclude on this hypothesis, many organo-carbonates will have to be synthesized in the presence of various amino acids, but also with other organic compounds having different physico-chemical properties (e.g., sugars, alkanes). Comparison between the properties of organo-carbonates and carbonates produced by bio- and inorganic mineralization (e.g., thermal stability, Fig.1-D) could be used as a criterion to distinguish bio-carbonates from organo-carbonates. However, to be able to assert the origin of a mineral, it is necessary to identify other criteria to corroborate these observations and thus accurately distinguish these two processes.
Acknowledgements: We gratefully acknowledge the technical support of S. BORENSZTAJN for the scanning electron microscopy (UPC, PARI platform - IPGP), S. NOWAK for X-ray diffraction analysis (UPC, X-ray platform) and A. CHEVILLOT-BIRAUD for the differential thermal analysis (UPC, ITODYS).
References:
[1] Tourney, J., & Ngwenya, B. T. (2009). Chemical Geology, 262(3-4), 138-146.
[2] Hoffmann, T. D., et al., (2021). Microbiology, 167(4), 001049.
[3] McMahon, S., & Cosmidis, J. (2022). Journal of the Geological Society, 179(2), jgs2021-050.
[4] Braissant, O., et al., (2003). Journal of Sedimentary Research, 73(3), 485-490.
[5] Xie, A. J., et al., (2005). Journal of Crystal Growth, 285(3), 436-443.
[6] Perron, A. , Paris, 2023.
[7] Wolf, S. E., et al., (2007). Angewandte Chemie International Edition, 46(29), 5618-5623.
[8] Perron, A., et al., (2023). Astrobiology, 23(4), 359-371.
How to cite: Perron, A., Vinogradoff, V., Stalport, F., Baudin, F., and Ménez, B.: Abiotic organo-minerals, a threat for identification of bio-minerals in hydrothermal systems and extraterrestrial environments, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1122, https://doi.org/10.5194/epsc2024-1122, 2024.