Ancient Rocks Show History of Atmospheric Oxygen

December 7, 2011

The creation of oxygen in Earth’s atmosphere was a long process of starts and stops, not a single continuous event, U.S. researchers say.

Geoscientists say the evidence comes from rock cores from a deep drilling project in northwest Russia in 2007. The Far Deep project drilled a series of 2-inch diameter cores and created a record of the chemistry of stone deposited during the Proterozoic Eon — 2,500 million to 542 million years ago — a release Tuesday from the National Science Foundation, which funded the research, said.

An analysis of the cores supports the conclusion that the Great Oxidation Event, the appearance of free oxygen in Earth’s atmosphere, played out over hundreds of millions of years.

“We’ve always thought that oxygen came into the atmosphere really quickly during an event,” Lee Kump, a geoscientist at Penn State University, said.

“We are no longer looking for an event,” he said. “Now we’re looking for when and why oxygen became a stable part of the Earth’s atmosphere.

“The definition of when an oxygen atmosphere occurred depends on which threshold you are looking for,” Kump said.

He said the cores showed that when red rocks containing iron oxides — the result of oxidation from atmospheric oxygen — appeared 2,300 million years ago, the air was still not breathable by animal standards because any oxygen in the atmosphere produced by the photosynthesis of early single-celled organisms was still being used up in the oxidation of sulfur, iron and other elements.