Multiple-sulphur isotope biosignatures

Variations in sulphur isotope ratios have been used as biosignatures in early rock records and Martian meteorites because some microbial sulphur metabolisms are known to produce large magnitude mass-dependent sulphur isotope fractionation. In order to establish the sulphur isotope biosignature, however, it becomes critically important to evaluate abiogenic processes that fractionate sulphur isotope ratios. A brief review is given here for the fundamental systematics and characteristics of multiple-sulfur isotope effects associated with (1) biological, (2) hydrothermal, and (3) photochemical processes. High-precision analysis of all four isotope abundance of sulphur may provide a unique constraint to establish biosignatures in space exploration.