2:30 PM - 2:45 PM
[MIS14-10] Elucidation of the mechanism of organic matter synthesis process by reducing reaction of clay minerals on the surface of the planet by STXM
Keywords:Organic matter, Origin of life, STXM, meteorite
[Background]
Many studies have been conducted to elucidate the evolutionary process of organic matter in extraterrestrial materials, which related to the formation of organic matter as a material for life. Elucidation of the process by which organic matter is synthesized from inorganic carbon (CO2) in the natural environment is important in considering primordial organic matter and its evolution. There is an evolutionary process in which several organic substances change to polycyclic aromatic hydrocarbons (PAHs) due to thermal stability, but the process of aliphatic carbon compounds formation, which cannot be explained by this process, requires further investigation. On the other hand, on Earth, it has been proposed that hydrogen and aliphatic carbon compounds may be produced near minerals containing Fe2+ such as serpentine and iron saponite (Sforma et al., 2018). However, in these studies, local chemical species analysis may be necessary to investigate the interaction between minerals and organic matter in detail, but its application is not yet sufficient.
The scanning transmission X-ray microscopy (STXM) is a method that enables chemical species analysis of carbon (C), nitrogen (N), and iron (Fe) with a spatial resolution of up to 30 nm, and it is important to apply this technique to meteorite and earth geological samples for the above purposes. In this study we analyzed the local chemical species of C and Fe in the Aguas Zarcas and Tagish Lake meteorites, which are expected to show water-mineral-organic interactions using STXM.
[Experiment]
Elemental mapping of C and Fe in thin FIB samples of meteorites were done using STXM at BL19A in KEK-PF. The experimental data were analyzed with aXis2000 (analysis of X-ray microscopy Images and Spectra), and the species mapping was performed using the absorption near edge structure (XANES) of each chemical element. Similarly, the XANES of magnesium (Mg) and aluminum (Al) were used to estimate the type of mineral around the organic matter.
[Results/Discussion]
In this study, based on the hypothesis that when Fe (II) in clay minerals is oxidized to Fe (III), organic matter is reduced to produce aliphatic carbon, the distinction between Fe(II) and Fe(III) and the distribution of carbon species (carbonic acid, aliphatic carbon, carboxylic acid, etc.) were investigated intensively in STXM analysis.
In the Aguas Zarcas meteorite, there was a concentration of aliphatic caron coexisting with carbonate near Fe (II).
In the Tagish Lake meteorite, the distribution of Fe (II) coincided with that of carbonate, suggesting the formation of siderite in some parts of the meteorite. In areas with low Fe (II), there was little carbonate, suggesting that carbonate was reduced during the oxidation of Fe (II) to Fe (III). Other peaks derived from carboxylic acids and carbon chains were also observed, but the peak intensities were not sufficient for mapping.
In the future, we plan to investigate how these materials were formed by preparing more appropriate samples, analyzing them by STXM, and conducting isotope analysis of the organic materials found in this study. As related materials, we will search for organic matter around secondary minerals in the dunite layer in the Oman ophiolite boring core samples and analyze the local speciation of carbon and iron.
Many studies have been conducted to elucidate the evolutionary process of organic matter in extraterrestrial materials, which related to the formation of organic matter as a material for life. Elucidation of the process by which organic matter is synthesized from inorganic carbon (CO2) in the natural environment is important in considering primordial organic matter and its evolution. There is an evolutionary process in which several organic substances change to polycyclic aromatic hydrocarbons (PAHs) due to thermal stability, but the process of aliphatic carbon compounds formation, which cannot be explained by this process, requires further investigation. On the other hand, on Earth, it has been proposed that hydrogen and aliphatic carbon compounds may be produced near minerals containing Fe2+ such as serpentine and iron saponite (Sforma et al., 2018). However, in these studies, local chemical species analysis may be necessary to investigate the interaction between minerals and organic matter in detail, but its application is not yet sufficient.
The scanning transmission X-ray microscopy (STXM) is a method that enables chemical species analysis of carbon (C), nitrogen (N), and iron (Fe) with a spatial resolution of up to 30 nm, and it is important to apply this technique to meteorite and earth geological samples for the above purposes. In this study we analyzed the local chemical species of C and Fe in the Aguas Zarcas and Tagish Lake meteorites, which are expected to show water-mineral-organic interactions using STXM.
[Experiment]
Elemental mapping of C and Fe in thin FIB samples of meteorites were done using STXM at BL19A in KEK-PF. The experimental data were analyzed with aXis2000 (analysis of X-ray microscopy Images and Spectra), and the species mapping was performed using the absorption near edge structure (XANES) of each chemical element. Similarly, the XANES of magnesium (Mg) and aluminum (Al) were used to estimate the type of mineral around the organic matter.
[Results/Discussion]
In this study, based on the hypothesis that when Fe (II) in clay minerals is oxidized to Fe (III), organic matter is reduced to produce aliphatic carbon, the distinction between Fe(II) and Fe(III) and the distribution of carbon species (carbonic acid, aliphatic carbon, carboxylic acid, etc.) were investigated intensively in STXM analysis.
In the Aguas Zarcas meteorite, there was a concentration of aliphatic caron coexisting with carbonate near Fe (II).
In the Tagish Lake meteorite, the distribution of Fe (II) coincided with that of carbonate, suggesting the formation of siderite in some parts of the meteorite. In areas with low Fe (II), there was little carbonate, suggesting that carbonate was reduced during the oxidation of Fe (II) to Fe (III). Other peaks derived from carboxylic acids and carbon chains were also observed, but the peak intensities were not sufficient for mapping.
In the future, we plan to investigate how these materials were formed by preparing more appropriate samples, analyzing them by STXM, and conducting isotope analysis of the organic materials found in this study. As related materials, we will search for organic matter around secondary minerals in the dunite layer in the Oman ophiolite boring core samples and analyze the local speciation of carbon and iron.