Earth’s atmosphere may have contained life-supporting oxygen much earlier than we thought. (Photo: Reuters)

Earth's atmosphere may have contained oxygen much earlier than the current timetable of our history predicts, according to new research from the University of British Columbia. After studying the chemical composition of the oldest soils on Earth, scientists from the university found evidence that oxygen was present in the layer of gases surrounding Earth as early as 3 billion years ago.

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That's about 700 million years earlier than previously thought.  

Sean Crowe, an assistant professor in the department of Microbiology and Immunology and the department of Earth, Ocean and Atmospheric Sciences at the University of British Columbia, led the study. Crow and his team looked at 3-billion-year-old rocks drilled from 1,000 meters below ground in South Africa. They focused on the levels of chromium and other metals in the samples.

According to Science News, the researchers compared the stable forms of chromium to look for signs of oxygen exposure. Today, there's far more chromium-52 present in land sediments than chromium-53, because oxygen in the Earth's atmosphere more readily oxidizes, or tears electrons from, chromium-53. The process is known as weathering.

But Crowe's team actually found surprisingly low levels of chromium-53 in the sediments, suggesting there was oxygen around back then. And if there was oxygen in the atmosphere 3 billion years ago, something had to be around to put it there.  

"The fact oxygen is there requires oxygenic photosynthesis, a very complex metabolic pathway, very early in Earth's history," Crowe told Live Science. "That tells us it doesn't take long for biology to evolve very complex metabolic capabilities."

This means that cyanobacteria, also known as blue-green algae, one of the first microorganisms on Earth, started photosynthesizing long before the Great Oxygen Event occurred. Photosynthesis would have been the source of any oxygen in the atmosphere billions of years ago. If anything, this new study further complicates our understanding of how the Earth's atmosphere evolved to what it is today.

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