From: University of British Columbia
Published September 18, 2017 11:38 AM

Changes in Earth's Crust Caused Oxygen to Fill the Atmosphere

Scientists have long wondered how Earth’s atmosphere filled with oxygen. UBC geologist Matthijs Smit and research partner Klaus Mezger may have found the answer in continental rocks that are billions of years old.

“Oxygenation was waiting to happen,” said Smit. “All it may have needed was for the continents to mature.”

Earth’s early atmosphere and oceans were devoid of free oxygen, even though tiny cyanobacteria were producing the gas as a byproduct of photosynthesis. Free oxygen is oxygen that isn’t combined with other elements such as carbon or nitrogen, and aerobic organisms need it to live. A change occurred about three billion years ago, when small regions containing free oxygen began to appear in the oceans. Then, about 2.4 billion years ago, oxygen in the atmosphere suddenly increased by about 10,000 times in just 200 million years. This period, known as the Great Oxidation Event, changed chemical reactions on the surface of the Earth completely.

Smit, a professor in UBC’s department of earth, ocean & atmospheric sciences, and colleague, professor Klaus Mezger of the University of Bern, were aware that the composition of continents also changed during this period. They set out to find a link, looking closely at records detailing the geochemistry of shales and igneous rock types from around the world — more than 48,000 rocks dating back billions of years.

Read more at University of British Columbia

Image: Matthijs Smit of the University of British Columbia examines ancient rocks from the deep crust in Norway during the summer of 2017. (Credit: Matthijs Smit)

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