Rocks from a core nearly a kilometre long show oxygen appeared on Earth millions of years earlier than previously thought. In the past it was thought oxygen first appeared somewhere around 2.3 or 2.4 billion years ago – known as the Great Oxidation Event – but the new rock cores show there was at least a whiff of oxygen around 100 million years earlier (Reuters, AP).
A group of researchers from Maryland found unexpected variations in sulfur chemistry in a section of a 908m long rock core of Mt. McRae Shale from Australia’s Hamersley Basin. Another team from Arizona State University then found corresponding variations in metal abundance. Taken together these indicated the presence of oxygen in a section of the core dated as older than the Great Oxidation Event.
“The Mount McRae record of sulfur isotopes captures the widespread and possibly permanent activation of the oxidative sulfur cycle for perhaps the first time in Earth’s history,” write Alan J. Kaufman and co. in this week’s Science. “The data suggest that oxygenation of the surface ocean preceded pervasive and persistent atmospheric oxygenation by 50 million years or more.” Ariel Anbar’s team found the same rock was enriched with the metals molybdenum and rhenium. Reactions involving oxygen probably weathered these metals out of crustal minerals into the oceans, before they went on to form part of the shale. ”These findings point to the presence of small amounts of O2 in the environment more than 50 million years before the start of the Great Oxidation Event.”
The instant reaction might be ‘so what’ – at most this pushes back our estimates of when oxygen appeared by less than 5%. However the finding could have important implications for life on Earth. The Great Oxidation Event saw Earth go from oxygen-poor to oxygen-rich very quickly. These new findings could suggest ancestors of plants were producing oxygen before this event. “What we have now are new lines of evidence for oxygen in the environment 50 to 100 million years before its big rise,” says Anbar (NSF press release).
“We believe that these findings are a significant step in our understanding of the oxygenation of Earth because they link changes in the environment with that of the biosphere,” adds Kaufman (UM press release).
Image: new findings reveal the importance of oxygen in the environment shortly before the deposition of this massive formation of iron oxide—rust—in the Hamersley Basin in Western Australia / AD Anbar, ASU