1 October 2007 Stable sulfur isotopes as probes for ancient life in the solar system
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Abstract
Secular changes in the stable sulfur isotope composition of seawater sulfate on Earth range from approximately 25 to 30 per mil (CDT). Minimal fractionation has been observed for the direct assimilation of seawater sulfate by plants into the two sulfur containing protein amino acids, methionine and cysteine. Similarly, sulfur isotope fractionation appears to be minimal with increasing trophic level. Thus, in theory, secular changes in the stable sulfur isotope composition of sulfur containing amino acids in ancient marine organisms should mimic that of seawater sulfate. The presence of sulfur containing amino acids elsewhere in the solar system and a comparison of their respective stable sulfur isotope values to those of sulfate containing minerals of similar ages may provide an alternative approach for determining the occurrence of past extraterrestrial life.
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Michael H. Engel, "Stable sulfur isotopes as probes for ancient life in the solar system", Proc. SPIE 6694, Instruments, Methods, and Missions for Astrobiology X, 66940B (1 October 2007); doi: 10.1117/12.731688; https://doi.org/10.1117/12.731688
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