Oxygen from 2.5 Billion Years Ago Found in Ocean Sedimentary Core Sample

A team of international scientists from a consortium of American and Canadian universities has added new evidence to the search for the earliest traces of oxygen, which gives scientists clues to solving the mystery of the origins of oxygen on Earth.

Researchers have determined that there was a "whiff," a "hint," of oxygen in Earth's atmosphere approximately 100 million yeas before previously known.

Until now, it has been believed that there were negligible amounts of oxygen on Earth up until about 2.4 billion years ago, a date which marks the occurrence of what is known as the Great Oxygen Event (GOE). This is when oxygen levels rose sharply from very low levels.

Researchers from five universities extracted a sedimentary rock core sample from the oceanic Hamersley Basin in Western Australia for analysis. Robert Creaser and postgraduate research student Brian Kendall, two researchers from the University of Alberta (UA), Canada, applied new rhenium dating methodology to determine the age of the earliest rhenium deposits in relation the to shale it was found in.

Rhenium accumulation in shale occurs only when oxygen is present in the overlying seawater: any presence of rhenium in shale points to a presence of oxygen. Rhenium is a radioactive element and so can be used for absolute dating.

Creaser and Kendall showed that the rhenium enrichment was the same age as the shale it was found in. Both date to 2.5 billion years ago, which is 100 million years before the GOE, thus proving that indicators of the presence of oxygen in the oceans predate the GOE.

"This finding provides us with a record of something we didn't know before, and that's significant in itself," said Creaser, a geologist at UA and a co-author of the study.

A team of researchers, Timothy Lyons, Steven Bates, and Clinton Scott, from the University of California, Riverside (UCR) analyzed the sedimentary core for the presence of proxy indicators--fingerprints--of oxygen's presence in the overlying seawater. The two indicators were metals and sulfur trapped in the sedimentary core.

Their research shows that the presence of oxygen on Earth increased significantly--although briefly--100 million years before its permanent introduction into Earth's history at the Great Oxygen Event around 2.4 billion years ago.

The new research findings confirming the small but significant amounts of oxygen 2.5 billion years ago in Earth's oceans and most likely also in Earth's atmosphere indicates that the evolution of oxygen producing organisms occurred prior to the GOE, and that oxygen buildup in Earth's atmosphere was more gradual than sudden.

Creaser, of UA, said: "Our research indicates there were oxygen producing organisms for many millions of years before the Great Oxidation Event, and then perhaps a 'tipping point' was reached, which launched the Great Oxidation Event."

Lyons, of UCR, said. "And the fact that...independent lines of evidence point in the same direction suggests that Earth's most dramatic shift in atmospheric composition and its relationship to the evolution of life began earlier and was more complex than most imagined."

The findings are reported in "A Whiff of Oxygen Before the Great Oxidation Event?" in the journal Science. Authors on the paper include AD Anbar, Y Duan, GL Arnold and GW Gordon from Arizona State University, C Scott and TW Lyons from the University of California - Riverside, B Kendall and RA Creaser from the University of Alberta, AJ Kaufman from the University of Maryland, and J Garvin and R Buick from the University of Washington

"Discovery challenges timeline of oxygen on Earth," University of Alberta;

"Researchers detect hint of oxygen 50 to 100 million years earlier than first believed," University of California, Riverside.