Oxygen Appeared in Earth’s Atmosphere 3 Billion Years Ago

An analysis of three-billion-year-old soils from South Africa shows that oxygen appeared in the atmosphere more than 600 million years earlier than previously thought.

Some of the rocks that Dr Crowe and his colleagues studied in South Africa. Image credit: Nic Beukes.

Some of the rocks that Dr Crowe and his colleagues studied in South Africa. Image credit: Nic Beukes.

Previous studies have indicated that oxygen began accumulating in the atmosphere only about 2.3 billion years ago during a dynamic period in Earth’s history referred to as the Great Oxygenation Event.

The new study, published in the journal Nature, provides evidence for low concentrations of atmospheric oxygen in 3-billion-year-old Nsuze paleosol, the oldest soil on Earth.

“We’ve always known that oxygen production by photosynthesis led to the eventual oxygenation of the atmosphere and the evolution of aerobic life,” said study lead author Dr Sean Crowe from the University of British Columbia.

“This study now suggests that the process began very early in Earth’s history, supporting a much greater antiquity for oxygen producing photosynthesis and aerobic life.”

There was no oxygen in the atmosphere for at least hundreds of millions of years after the Earth formed.

This is a micrograph of 3-billion-year-old sericite-rich paleosol. Image credit: Sean A. Crowe et al.

This is a micrograph of 3-billion-year-old sericite-rich paleosol. Image credit: Sean A. Crowe et al.

Today, the Earth’s atmosphere is 20 per cent oxygen thanks to photosynthetic bacteria that, like trees and other plants, consume carbon dioxide and release oxygen. The bacteria laid the foundation for oxygen breathing organisms to evolve and inhabit the planet.

“These findings imply that it took a very long time for geological and biological processes to conspire and produce the oxygen rich atmosphere we now enjoy,” said second author Dr Lasse Døssing from the University of Copenhagen.

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Bibliographic information: Sean A. Crowe et al. 2013. Atmospheric oxygenation three billion years ago. Nature 501, 535–538; doi: 10.1038/nature12426