Ancient Soils Reveal Earth’s Oxygen Appeared 700 Million Years Earlier Than Believed

A recent analysis of a three billion year old soil offers clues about early life on Earth, raising questions about the evolution of early life.

A team of researchers from the University of Copenhagen and the University of British Columbia examined the chemical composition of ancient soils from South Africa and claim that oxygen appeared in the atmosphere nearly 700 million years earlier than previously thought. A thorough analysis of the soil component yielded low concentrations of atmospheric oxygen.

This new finding debunks the previous theory that claimed the first production of Oxygen on earth was 2.5 billion years ago during a period known as the Great Oxidation Event (GOE),  which brought about a tremendous change in the surface environments of Earth and gave rise to advanced life. This finding was done by Winthrop Professor Mark Barley, from the University of Western Australia's Centre in collaboration with colleagues from the University of Alberta led by Professor Kurt Konhauser. This study discovered how the links between ocean, tectonics and land chemistry gave rise to life on earth 2.5 billion years ago.

This latest research was conducted by Sean Crowe, the co author of the study and an assistant professor in the Department of Microbiology and Immunology, and Earth, Ocean and Atmospheric Sciences at UBC.

The researchers investigated two geological layers in South Africa. One was Nsuze paleosol and the other was Ijzermyn iron formation. One of the most ancient preserved soils on earth is Nsuze Paleosol that is clubbed between volcanic rocks and sedimentary rocks. They analyzed these two samples to detect the ratios of chromium isotopes present in the rock samples, as chromium is a strong indicator of the level of oxygen. On analyzing the samples, the researchers detected higher propositions of chromium isotopes that are formed from oxidation. Apart from this, they discovered huge content of an isotope of uranium that is also a result of oxidation.

"We've always known that oxygen production by photosynthesis led to the eventual oxygenation of the atmosphere and the evolution of aerobic life. 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," Crowe said in a press statement.

According to the study reports, for at least hundreds of millions of years after the earth formed, there was literally no oxygen in the atmosphere. But photosynthetic bacteria, which like plants and trees  consume carbon dioxide and produces oxygen, supplied the earth's atmosphere with the oxygen. These bacteria made it possible for the 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," says Lasse Dossing, the other lead scientist on the study, from the University of Copenhagen.

The findings have been documented in the journal Nature.