Are volcanoes behind the oxygen we breathe?

It is widely believed that Earth's atmosphere has been rich in oxygen for about 2.5 billion years due to a relatively rapid increase in microorganisms capable of performing photosynthesis. Researchers provide a mechanism to explain precursor oxygenation events, or 'whiffs,' which may have opened the door for this to occur. Their findings suggest volcanic activity altered conditions enough to accelerate oxygenation, and the whiffs are an indication of this taking place.