Biomolecule breakdown is inorganic

After organisms die, their biomolecules decompose and end up on ocean floors and integrated into sediments, where they can eventually become oil and natural gas. It's long been thought that microbial processes could be responsible for the initial transformations of biomolecules such as β-carotene, steroids, and terpenoids into biomarker compounds such as carotane, phytane, and steranes. But now, researchers show that abiotic processes may in fact be responsible. Yanek Hebting, now a postdoc at MIT, and colleagues at Louis Pasteur University in Strasbourg and ETH Zurich, studied a number of reduced carotenoids in samples of sediment from Lake Cadagno in Switzerland. They found that the reductions were not stereospecific, and therefore, not biologically produced (Science, published online May 11, dx.doi.org/10.1126/science.1128966). Rather, inorganic H₂S, produced by bacterial sulfate reduction, is likely responsible for reducing the biomolecules, a hypothesis strengthened by the group's laboratory experiments.