Among the various geochemical proxies for the presence of molecular oxygen in the environment, molecular fossils offer a unique record of oxygen where it was first produced and consumed by biology: in sunlit aquatic habitats. Steroid biosynthesis requires molecular oxygen, making the study of sterane molecular fossils important in reconstructing early environmental conditions. In a new study, NAI-funded scientists and their colleagues present evidence that microaerobic marine environments where steroid biosynthesis was possible could have been widespread and persistent for long periods of time prior to the earliest evidence for atmospheric oxygen. Their study is published in a recent issue of PNAS.

Source: NAI newsletter