David Gold, a post-doc in the Summons lab at MIT, is the lead author of a new paper in Nature –Paleoproterozoic sterol biosynthesis and the rise of oxygen. His findings suggest that eukaryotic organisms were present on Earth as early as 2.31 billion years ago, around the same time that oxygen was first present in the Earth’s atmosphere. This finding significantly pushes back the earliest signs of eukaryotes. Previously, the oldest known eukaryotes were algae-like fossils from 1.56 billion years ago.
David and his co-authors arrived at this conclusion by doing a molecular clock analysis of the genes associated with sterol biosynthesis. They constrained their molecular clock with fossil evidence and used multiple molecular clock analyses. These analyses constrained the evolution of sterol biosynthesis to approximately 2.31 billion years ago. Complex sterols are unique to eukaryotes and producing them is an oxygen-intensive process. Therefore, these biomarkers are evidence of both eukaryotic life and an oxygenated atmosphere. Previously, it appeared that the evolution of sterol biosynthesis lagged behind the oxygenation of the atmosphere. However, this study suggests that this evolutionary event is tied to the availability of oxygen in the atmosphere.