Recombination reactions as a possible mechanism of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth.
basic_science · Level V
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- Also identified by DOI 10.1073/pnas.1620977114 and PMC identifier 5373401.
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Abstract
A hierarchy of isotopically substituted recombination reactions is formulated for production of sulfur allotropes in the anoxic atmosphere of Archean Earth. The corresponding system of kinetics equations is solved analytically to obtain concise expressions for isotopic enrichments, with focus on mass-independent isotope effects due to symmetry, ignoring smaller mass-dependent effects. Proper inclusion of atom-exchange processes is shown to be important. This model predicts significant and equal depletions driven by reaction stoichiometry for all rare isotopes: <sup>33</sup>S, <sup>34</sup>S, and <sup>36</sup>S. Interestingly, the ratio of capital [Formula: see text] values obtained within this model for <sup>33</sup>S and <sup>36</sup>S is -1.16, very close to the mass-independent fractionation line of the Archean rock record. This model may finally offer a mechanistic explanation for the striking mass-independent fractionation of sulfur isotopes that took place in the Archean atmosphere of Earth.