posted 05-12-2016 10:33 AM               

"We've found a way to sample a part of the ancient Earth that we've never been able to investigate before," said Andrew Tomkins, a geologist at Monash University in Melbourne. "And we can show that the upper atmosphere 2.7 billion years ago was oxygen-rich compared to the lower atmosphere."

The finding, published Wednesday in Nature, is surprising because other lines of evidence strongly suggest that there was essentially no oxygen in the lower atmosphere at that time.

"It is a truth almost universally acknowledged that Earth's atmosphere before about 2.5 billion years ago had little or no free oxygen," wrote Kevin Zahnle of NASA Ames Research Center and Roger Buick of the astrobiology program at the University of Washington, in an independent analysis of the study.

Tomkins, who led the research, said he and his team were surprised by the findings as well.