Ancient soils of Earth and Mars
Datum
2023-03-24
Autor:innen
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University of Oregon
Zusammenfassung
Three to four billion years ago the surface of Mars may have been habitable. Ancient martian rocks that were subject to aqueous alteration in near-surface environments may store a record of this habitable paleoclimate, and they may also be favorable environments for the preservation of biosignatures. Some of the oldest altered rocks on Mars appear to be similar in mineralogy and geochemistry to ancient, buried soils (paleosols) on Earth. By using terrestrial paleosols as an analog for Mars, this dissertation seeks to constrain the organic preservation potential of martian paleosols. This is a first step towards understanding if putative martian paleosols should be considered high priority targets for in-situ drilling campaigns and sample return to Earth.The objectives of this work were to a) identify the factors that have led to enhanced preservation of organic matter in terrestrial paleosols from throughout Earth’s 3.7 billion year old geological record; b) determine if the mineralogy and alteration history of Eocene (33 million-year-old) paleosols from eastern Oregon can be identified with Mars rover-like instruments; and c) determine if trace amounts of organic carbon in the Oregon paleosols can be detected with evolved gas analysis (EGA), a technique currently employed by the NASA Curiosity Mars Rover to search for past signs of life on Mars. A data compilation of previously published organic matter content of paleosols spanning ~3 billion years of Earth history showed that soil redox state before burial was a major factor that was associated with enhanced preservation of organic matter in paleosols. Chemically reduced paleosols were found to preserve organic carbon at abundances two to three orders of magnitude greater than oxidized paleosols. Next, evolved gas analysis, spectroscopy, and x-ray diffraction were determined to be suitable techniques for constraining the mineralogy and alteration history of 33-million-year-old paleosols from Oregon. Very low amounts of organic carbon (~0.01 wt. %) and fragments of organic molecules in oxidized paleosols were able to be observed with EGA, suggesting these techniques may be suitable for detecting low amounts of organic carbon in similar materials on Mars. This work indicates that putative paleosols / weathering profiles on Mars should be considered high priority targets for in-situ biosignature detection and eventual sample return to Earth.
Beschreibung
Schlagwörter
astrobiology, evolved gas analysis, martian paleosols, pedogenic weathering, terrestrial analogs, weathering profile