Mercury abundance and isotopic composition indicate subaerial volcanism prior to the end-Archean “whiff” of oxygen

Significance Earth’s atmosphere became oxygenated around 2.4 billion years ago, and this event was preceded by at least one short-lived “whiff” of free O 2 gas nearly 100 million years earlier. The cause of this whiff has so far been difficult to identify. Here, we present mercury concentrations and isotope ratios across the whiff interval and find evidence for significant subaerial volcanism immediately preceding oxygenation. We propose that subaerial weathering of fresh volcanic rocks acted as a fertilizer that stimulated biological productivity and O 2 production in the surface ocean. Our results indicate another strong linkage between planetary magmatic processes and the evolution of Earth’s atmosphere.