Earth's oxygen-rich atmosphere emerged in whiffs from a kind of blue-green algae in shallow oceans around 2.5 billion years ago, revealed a new study from Canadian and US scientists.
These whiffs of oxygen likely happened in the following 100 million years, changing the levels of oxygen in Earth's atmosphere until enough accumulated to create a permanently oxygenated atmosphere around 2.4 billion years ago - a transition widely known as the Great Oxidation Event.
Brian Kendall of the University of Waterloo said, "The onset of Earth's surface oxygenation was likely a complex process characterized by multiple whiffs of oxygen until a tipping point was crossed. Until now, we haven't been able to tell whether oxygen concentrations 2.5 billion years ago were stable or not. These new data provide a much more conclusive answer to that question."