Researchers Find Earliest Signs of Oxygen on Earth

Two teams of scientists have discovered signs of the Earth's first breaths -- the earliest signs of rising atmospheric oxygen -- far earlier than previously believed, according to research news from Arizona State University (ASU).

"What we have now are two new lines of evidence for there being some oxygen in the environment 50 million to 100 million years before the big rise of oxygen," said Ariel Anbar, an associate professor in ASU's School of Earth and Space Exploration and Department of Chemistry and Biochemistry in the College of Liberal Arts and Sciences. "This knowledge is relevant to today's global studies of environmental and climate issues, because it helps us understand the interactions between biology, geology and the composition of the atmosphere."

Anbar and other scientists on the teams found evidence of small but significant amounts of oxygen in the oceans, and possibly the atmosphere, in sedimentary rocks about 2.5 billion years old. Atmospheric oxygen did not exist when the Earth first formed about 4.56 billion years ago, and significant levels of oxygen did not arise until 2.3 billion to 2.4 billion years ago, a period dubbed the "Great Oxidation Event."

"We seem to have captured a piece of time before the Great Oxidation Event during which the amount of oxygen was actually changing - caught in the act, as it were," Anbar said.

Anbar led one of the research teams and took part in the other. The research effort brought together scientists from ASU, the University of Maryland, the University of Washington, the University of California-Riverside and the University of Alberta. Funding and support came from the Astrobiology Drilling Program of NASA's Astrobiology Institute, the National Science Foundation and the Geological Survey of Western Australia.

The scientists found the evidence of early oxygen in a 908-meter-long (nearly 3,000-foot-long) core of sedimentary rock drilled from the Hamersley Basin in western Australia. The teams sliced the core in half lengthwise, leaving half archived in Australia and bringing the other half to ASU for further research.

While the researchers' goal initially was only to determine what the environment and ocean life was like before the Great Oxidation Event, both teams were surprised to discover concentrations of metal deposited in that time period that indicated the presence of oxygen.

"We expected these analyses to be boring," said Gail Arnold, an assistant research scientist with the ASU team. "Instead of it being boring, we found this big change."

In addition to helping to better understand the interactions of life and geophysical processes on Earth, the teams' discoveries could also provide insights into potential life on other planets, Anbar said.

"It ... has implications for the search for life on planets outside our solar system because, in the near future, the only way we can look for evidence of life in such far-off places is to look for the fingerprints of biology in the compositions of their atmospheres," he said. "We are not far off from being able to detect Earth-like planets elsewhere in the galaxy, and eventually we will be able to use telescopes to measure the oxygen content of their atmospheres. If we find that none of them have undergone a Great Oxidation Event, what will that mean about life? Is it inevitable that the evolution of oxygen-producing organisms results in an oxygen-rich atmosphere? Our results indicate that the connection is not so simple."

Arizona State University, "Research Points to Earth's First Breaths." URL: (http://asunews.asu.edu/20070927_earthoxygen)