According to an article that appeared September 25 in the journal Nature, the appearance of oxygen in the atmosphere occurred as much as 700 million years earlier than scientists had previously believed.  The discovery is now raising questions about the evolution of early life on our planet.

“It is widely assumed that atmospheric oxygen concentrations remained persistently low (less than 10−5 times present levels) for about the first 2 billion years of Earth’s history. The first long-term oxygenation of the atmosphere is thought to have taken place around 2.3 billion years ago, during the Great Oxidation Event. Geochemical indications of transient atmospheric oxygenation, however, date back to 2.6–2.7 billion years ago,” wrote the researchers in the study’s abstract.