Biogeochemical impact of nickel and urea in the great oxidation event

The Great Oxidation Event marks the first substantial increase in atmospheric oxygen on Earth. Despite the oxygenic photosynthesis that emerged hundreds of million years before this event, the specific biogeochemical mechanisms responsible for maintaining low oxygen levels for an extended period remain elusive. Here, we show the critical role of urea as a nitrogen source for cyanobacteria, the cascading impact of nickel on abiotic urea production, and their combined effects on the proliferation of cyanobacteria leading to the great oxidation event. Urea formation was experimentally evaluated under simulated Archean conditions and cyanobacterial growth was monitored providing urea as the nitrogen source. Our findings demonstrate that urea can be produced in the Archean cyanobacterial habitats with UV-C irradiation, shedding light on the controversy regarding the evolution of nitrogen-fixing enzymes in primitive cyanobacteria. We propose that environmental conditions in the early Archean, characterized by elevated urea and nickel concentration, may have hindered cyanobacterial expansion, contributing to the delay between the evolution of oxygenic photosynthesis and the onset of the great oxidation event.