November 20, 2015

Earth’s oxygen-rich atmosphere began in fits-and-starts

(November 20, 2015)  ASU scientist Ariel Anbar helped lead research team solving the puzzle of Earth’s Great Oxidation Event

Earth's oxygen-rich atmosphere emerged as transient “whiffs” in shallow oceans around 2.5 billion years ago, according to new research 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.

“One of the questions we ask is: ‘Did the evolution of photosynthesis lead directly to an oxygen-rich atmosphere? Or did the transition to today's world happen in fits-and-starts?" said Ariel Anbar, President's Professor in Arizona State University’s School of Earth and Space Exploration (SESE) and the School of Molecular Sciences (SMS). “How and why Earth developed an oxygenated atmosphere is one of the most profound puzzles in understanding the history of our planet.”

The findings are presented in a paper published this month in Science Advances from researchers at University of Waterloo, University of Alberta, Arizona State University, University of California Riverside, and Georgia Institute of Technology. The team presents new isotopic data showing that a burst of oxygen production by photosynthetic cyanobacteria temporarily increased oxygen concentrations in Earth's atmosphere.

“The onset of Earth's surface oxygenation was likely a complex process characterized by multiple whiffs of oxygen until a tipping point was crossed,” said Brian Kendall, a professor of Earth and Environmental Sciences at the University of Waterloo, who led the study. “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.”

Kendall was a visiting student, postdoctoral fellow, and faculty research associate at Arizona State University from 2006-2012, where he worked with Anbar.

The new data support a hypothesis proposed by Anbar, Kendall, and other collaborators in 2007. In Western Australia, they found preliminary evidence of these oxygen whiffs in black shales deposited on the seafloor of an ancient ocean.

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