Anoxic photo-oxidation of Mn(II)-bearing carbonates on Mars and early Earth

, 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.

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Publication Details

Journal
Proceedings of the National Academy of Sciences
Published
2026-05-11
DOI
https://doi.org/10.1073/pnas.2607260123
Primary Topic
Planetary Science and Exploration
Type
article
Field-Weighted Citation Impact
0.00

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article

Anoxic photo-oxidation of Mn(II)-bearing carbonates on Mars and early Earth

W L Zhang, David C. Catling, Yuke Zhu, Paul G. Falkowski et al.
Proceedings of the National Academy of Sciences
Planetary Science and Exploration
article

Anoxic photo-oxidation of Mn(II)-bearing carbonates on Mars and early Earth

W L Zhang, David C. Catling, Yuke Zhu, Paul G. Falkowski, Jihua Hao, Lu Pan, Jiye Guo, Nicholas J. Tosca, Yi Liu, Amrit S. Chaddha, Yunguo Li, Jie Li, Anya Huo, Pengcheng Ju, Fang Huang, Zongbin Zhang
article en

Abstract

, 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.

Proceedings of the National Academy of SciencesVol. 123(20)
Rutgers, The State University of New Jersey (US), University of Science and Technology of China (CN), Planetary Science Institute (US), University of Cambridge (GB), China National Space Administration (CN), Rutgers Sexual and Reproductive Health and Rights (NL), Institute of Geodesy and Geophysics (CN), Department of Chemistry and Earth Sciences (BY), National Synchrotron Radiation Laboratory (CN), Earth and Space Research (US)
National Aeronautics and Space Administration, National Natural Science Foundation of China, Chinese Academy of Sciences, Ministry of Science and Technology of the People's Republic of China, NASA Astrobiology Institute
Openalex Percentile: Top 6%
Planetary Science and Exploration
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