Permanent Oxygenation of Earth’s Atmosphere Occurred Later than Previously Thought
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Oxygen levels fluctuated dramatically for about 200 million years after the start of the Great Oxidation Event, with permanent atmospheric oxygenation finally arriving about 2.22 billion years ago, some 100 million years later than previously estimated, according to new research led by University of Leeds Professor Simon Poulton.

The permanent rise of oxygen in the atmosphere of Earth, which set the stage for life as we know it, happened 100 million years later than previously thought. Image credit: Hadeano.

A significant rise of atmospheric oxygen fundamentally changed the chemistry of surface environments and the nature of Earth’s habitability.

Early atmospheric oxygenation occurred about 2.43 billion years ago, marking the start of the Great Oxidation Event.

By analyzing marine sediments from South Africa’s Eastern Transvaal Basin that formed during this event, Professor Poulton and colleagues discovered that early atmospheric oxygenation was short-lived, and oxygen did not become a permanent feature of the atmosphere until much later.

“The Great Oxidation Event fundamentally changed Earth’s environment and habitability,” Professor Poulton said.

“This early period of oxygenation was thought to have occurred between about 2.43 and 2.32 billion years ago.”

“However, our research shows that, in fact, oxygenation of the atmosphere was highly unstable over a period of about 200 million years, with permanent atmospheric oxygenation occurring about 100 million years later that previously thought.”

The findings also suggest a direct link between fluctuations in atmospheric oxygen concentration and greenhouse gas concentrations.

“These findings help explain four widespread glaciations that occurred coincident with the Great Oxidation Event, some of which were likely to have covered the whole of the Earth in ice for millions of years,” said Professor Andrey Bekker, a researcher at the University of California-Riverside.

“Our new data show that the permanent rise of oxygen actually occurred after the final major glaciation of the period and not before it, which had previously been a major puzzle in our understanding of links between early atmospheric oxygenation and intense climatic instability.”

The study authors have re-labeled this period the Great Oxidation Episode.

It ushered in a 1.5 billion year period of subsequent climatic and environmental stability, which remained until a second major period of rising oxygen and climate instability at the end of the Precambrian period.

“We cannot begin to understand the causes and consequences of atmospheric oxygenation, the most significant control on Earth’s habitability, if we do not know when permanent atmospheric oxygenation actually occurred,” Professor Poulton said.

“Now at last we have that piece of the puzzle.”

The results are published in the journal Nature.

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S.W. Poulton et al. A 200-million-year delay in permanent atmospheric oxygenation. Nature, published online March 29, 2021; doi: 10.1038/s41586-021-03393-7

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