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Exoplanet Exploration

Calibration of Two Novel Biosignatures in Manganese Oxides: Biomolecule Mineral Templates and Oxygen Isotopes as Records of Manganese Oxidation Pathways

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Calibration of Two Novel Biosignatures in Manganese Oxides: Biomolecule Mineral Templates and Oxygen Isotopes as Records of Manganese Oxidation Pathways
Rocks and sediments enriched in manganese (Mn) oxides have been observed on Mars and in early Earth sedimentary strata; yet, little is known about the modern or paleo-environmental behavior of Mn. Mn(III/IV) oxides are receiving increasing attention as paleoredox indicators since oxidation of Mn(II) requires high redox potential oxidants. In fact, oxidation of Mn(II) by molecular oxygen is thermodynamically prohibited in the absence of (in)organic catalysts. Three general pathways exist for the oxidation of Mn(II): 1) mineral-catalyzed oxidation of adsorbed Mn(II), 2) direct enzymatic oxidation, and 3) reaction with superoxide produced by bacteria or fungi. Superoxide is also formed abiotically through various (photo)reactions and photolysis of water – conditions consistent with surface sediments exposed to UV radiation on early Earth and Mars. Thus, (a)biogenic superoxide production may be or has been a primary driver of Mn oxide formation on Earth and elsewhere. In this reservoir of Mn oxide minerals – we suggest there exist at least two viable, yet largely unexplored proxies that may harbor unique records of biological activity. Here we propose an integrated project that aims to simultaneously calibrate the potential for these proxies as tools for reconstructing mechanisms of manganese oxidation – with broad implications for predicting the presence and origin of life. More »

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