New evidence for first production of oxygen on Earth

Winthrop Professor Mark Barley, from The University of Western Australia's Centre for Exploration Targeting, and colleagues from the University of Alberta led by Professor Kurt Konhauser, made the discovery by examining key elements in banded iron formations through time.

The study, published in the journal Nature, has identified how links between tectonics and ocean and land chemistry combined to give rise to life on earth about 2.5 billion years ago, during a period known as the Great Oxidation Event (GOE). The GOE changed surface environments on Earth and ultimately made advanced life possible.

Professor Barley said the research team found a rising abundance of chromium in the banded iron formations starting 2.48 billion years ago, which was an important indication of links between life and the growth of continents. Using this data, they were able to see cyanobacteria had started to produce oxygen, and that aerobic respiring chemolithotrophic bacteria oxidised pyrite linked to acid rock drainage that dissolved chromium on land and added chromium and sulphate to the ocean. This confirms that the 2.48 to 2.32 billion year period was the protracted Great Oxidation Event which eventually helped the formation of complex life.

Professor Barley said it was important to understand how and when oxygen levels rose and their links to organisms and the tectonic growth of continents.

"We live in a unique environment and Earth is the only planet we know that has an oxygen-rich atmosphere, as well as hydrosphere that is vital for complex life," he said.

"But the Earth's early atmosphere was oxygen-poor in the Archaean prior to the Great Oxidation Event, which happened between 2.5 and 2.3 billion years ago, so it's vital that we understand how oxygen rose."

"So we think we've resolved a major debate about when the bacteria that produced oxygen existed and how long it took for oxygen levels to rise enough to support growth of life on earth."

Professor Barley said there was possible evidence that photosynthetic bacteria (cyanobacteria) may have evolved at least 2.7 billion years ago, but the oldest unambiguous microbial fossils of cyanobacteria that had been found were preserved quite a long time after the atmosphere became oxygen rich, between 2.5 and 2.3 billion years ago.