Earth’s early volcanic activity may have delayed evolution of life

New Scientist : One reason complex life exists on Earth is the presence of oxygen in the planet’s atmosphere. The Great Oxygenation Event (GOE), which occurred some 2.5 billion years ago, was a major environmental change during which atmospheric oxygen reached levels comparable to those today. Although it had been proposed that the oxygen was produced by ocean-dwelling cyanobacteria, those organisms existed millions of years before the GOE. In a paper published in Nature Geoscience, researchers say that iron toxicity may explain the gap between the first appearance of those photosynthesizing bacteria and the oxygenation of Earth’s atmosphere. Copious amounts of iron may have been spewed into the early oceans by subsea volcanic activity. Not only did the iron poison the cyanobacteria and inhibit their photosynthesizing, but the iron also chemically captured any free oxygen they produced. It was only when those oxygen sinks became saturated that excess free oxygen started to accumulate in the atmosphere and led to the GOE.