Anoxic photo-oxidation of Mn(II)-bearing carbonates on Mars and early Earth
Abstract
Manganese oxides, thought to form almost exclusively through reactions between Mn 2+ and O 2 , catalyze oxidative transformations among redox-sensitive metals. Thus, the occurrence of Mn oxides, either observed or inferred from sedimentary geochemical data, has formed the basis for multiple hypotheses concerning the evolution of the atmospheric redox state on the early Earth and Mars. Here, using theory and experiments, we report that the band gap of common Ca/Mg carbonate minerals (including calcite, magnesite, and aragonite) is significantly lowered by trace incorporation (0.8 wt% or lower) of Mn(II) into their bulk structure or surface, conferring photochemical reactivity under ultraviolet conditions relevant to early Earth and Mars (200 to 400 nm). Moreover, we show that surface incorporation of Mn(II) reduces the fundamental band gap much more effectively (by >1 eV) than bulk incorporation. Our results suggest that photo-oxidation of Mn(II)-bearing carbonates could have occurred widely on planetary surfaces, resulting in the abiotic formation of manganese oxides without free molecular oxygen. Photochemically driven redox cycling of manganese could help sustain redox disequilibria for microbial metabolisms, but compromises the use of manganese oxides as oxygen barometers.
Article Details
Journal Info
Proceedings of the National Academy of Sciences
National Academy of Sciences
Authors (16)
Jiye Guo
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Yuke Zhu
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Nicholas J. Tosca
Department of Earth Sciences, University of Cambridge
Lu Pan
School of Earth and Space Sciences, University of Science and Technology of China
David C. Catling
Department of Earth and Space Sciences and Cross-Campus Astrobiology Program, University of Washington
Yi Liu
Wenhua Zhang
Amrit S. Chaddha
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Pengcheng Ju
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Jie Li
Zongbin Zhang
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Anya Huo
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Yunguo Li
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China
Fang Huang
Paul G. Falkowski
Department of Chemistry and Chemical Biology, Rutgers University
Jihua Hao
State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China