Flooding Earth’s atmosphere with oxygen may not have needed a triggering event
SAN FRANCISCO — Maybe the trigger for the rise of oxygen on Earth was nothing special. Maybe that oxidation didn’t need large tectonic shifts or the evolution of land plants. Instead, the circulation of carbon dioxide, oxygen and phosphorus between Earth’s atmosphere, oceans, rocks and the simplest of photosynthesizing life forms is sufficient to produce the dramatic shifts in atmospheric gases that occurred in Earth’s history, new research suggests. “The [oxygen] transitions we see are driven by Earth’s nutrient cycles,” said Benjamin Mills, a biogeochemist and computer modeler at the University of Leeds in England, who presented the research December 10 at the American Geophysical Union’s annual meeting. The findings, led by Leeds geologist Lewis Alcott, were also published online December 10 in Science. Early Earth’s atmosphere was a steamy mix of water vapor, CO₂, ammonia, hydrogen sulfide and methane. Then, about 2.4 billion years ago, oxygen in the atmosphere suddenly skyrocketed, a surge known as the Great Oxidation Event (SN: 2/6/17). After another billion years or so, two...