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Proc Natl Acad Sci U S A. 2013 Jul 9;110(28):11238-43. doi: 10.1073/pnas.1305530110. Epub 2013 Jun 24.

Manganese-oxidizing photosynthesis before the rise of cyanobacteria.

Author information

1
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. jena@caltech.edu

Abstract

The emergence of oxygen-producing (oxygenic) photosynthesis fundamentally transformed our planet; however, the processes that led to the evolution of biological water splitting have remained largely unknown. To illuminate this history, we examined the behavior of the ancient Mn cycle using newly obtained scientific drill cores through an early Paleoproterozoic succession (2.415 Ga) preserved in South Africa. These strata contain substantial Mn enrichments (up to ∼17 wt %) well before those associated with the rise of oxygen such as the ∼2.2 Ga Kalahari Mn deposit. Using microscale X-ray spectroscopic techniques coupled to optical and electron microscopy and carbon isotope ratios, we demonstrate that the Mn is hosted exclusively in carbonate mineral phases derived from reduction of Mn oxides during diagenesis of primary sediments. Additional observations of independent proxies for O2--multiple S isotopes (measured by isotope-ratio mass spectrometry and secondary ion mass spectrometry) and redox-sensitive detrital grains--reveal that the original Mn-oxide phases were not produced by reactions with O2, which points to a different high-potential oxidant. These results show that the oxidative branch of the Mn cycle predates the rise of oxygen, and provide strong support for the hypothesis that the water-oxidizing complex of photosystem II evolved from a former transitional photosystem capable of single-electron oxidation reactions of Mn.

KEYWORDS:

Great Oxidation Event; X-ray absorption spectroscopy; pyrite; water oxidation

PMID:
23798417
PMCID:
PMC3710856
DOI:
10.1073/pnas.1305530110
[Indexed for MEDLINE]
Free PMC Article
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