title: Anoxic photochemical oxidation of siderite generates molecular hydrogen and iron oxides.
abstract: Photochemical reactions of minerals are underappreciated processes that can make or break chemical bonds. We report the photooxidation of siderite (FeCO3) by UV radiation to produce hydrogen gas and iron oxides via a two-photon reaction. The calculated quantum yield for the reaction suggests photooxidation of siderite would have been a significant source of molecular hydrogen for the first half of Earth's history. Further, experimental results indicate this abiotic, photochemical process may have led to the formation of iron oxides under anoxic conditions. The reaction would have continued through the Archean to at least the early phases of the Great Oxidation Event, and provided a mechanism for oxidizing the atmosphere through the loss of hydrogen to space, while simultaneously providing a key reductant for microbial metabolism. We propose that the photochemistry of Earth-abundant minerals with wide band gaps would have potentially played a critical role in shaping the biogeochemical evolution of early Earth.
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, USA.
authors.forename: J Dongun
authors.initials: JD
authors.lastname: Kim
authors.forename: Nathan
authors.initials: N
authors.lastname: Yee
authors.forename: Vikas
authors.initials: V
authors.lastname: Nanda
authors.forename: Paul G
authors.initials: PG
authors.lastname: Falkowski
mesh_terms: D000693:Anaerobiosis; D001272:Atmosphere / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D002254:Carbonates / Q000737:chemistry*; D018534:Earth, Planet; D019419:Evolution, Planetary; D018559:Exobiology / Q000379:methods*; D005290:Ferric Compounds / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008956:Models, Chemical; D010083:Oxidants, Photochemical / Q000737:chemistry; D010084:Oxidation-Reduction; D017785:Photons; D014466:Ultraviolet Rays
chemical_list: D002254:Carbonates; D005290:Ferric Compounds; D010083:Oxidants, Photochemical; D002245:Carbon Dioxide; C000499:ferric oxide; D006859:Hydrogen; C486982:siderite
keywords: Archean iron cycle; astrobiology; banded iron formations; photogeochemistry