What Delayed Earth’s Oxygenation?

Photosynthesizers using water, which releases oxygen, could not compete with those using iron. (Image: via   pixabay  /  CC0 1.0)
Photosynthesizers using water, which releases oxygen, could not compete with those using iron. (Image: via pixabay / CC0 1.0)

Powering a massive biosphere on Earth, photosynthesis is the light-mediated reaction that converts carbon dioxide and water to carbohydrates and oxygen. About 2.3 billion years ago, this reaction led to a dramatic oxygenation of Earth’s atmosphere.

Evidence exists for oxygen-releasing photosynthesis evolving much earlier — perhaps as early as 3 billion years ago. However, the oxygen-rich atmosphere we take for granted today has existed for only about 10 percent of Earth’s 4.5-billion-year history.

Why did oxygenation of the atmosphere occur so much later than the evolution of oxygen-releasing photosynthesis? Christopher Reinhard, an assistant professor in the School of Earth and Atmospheric Sciences (EAS), said:

Reinhard, former EAS postdoctoral researcher Kazumi Ozaki, and collaborators have proposed a solution to the puzzle. Their findings, published in Nature Communications, suggest that in the oceans of early Earth, oxygen-releasing photosynthesizers could not compete effectively with their primitive counterparts.

Modern photosynthesizers consume water and release oxygen. Primitive ones instead consume dissolved iron ions — which would have been abundant in the oceans of early Earth. They produce rust as a byproduct instead of oxygen.

Photosynthesizers using water, which releases oxygen, could not compete with those using iron. (Image: Georgia Institute of Technology)

Photosynthesizers using water, which releases oxygen, could not compete with those using iron. (Image: Georgia Institute of Technology)

Using experimental microbiology, genomics, and large-scale biogeochemical modeling, Ozaki, the paper’s first author and now an assistant professor in the Department of Environmental Science at Toho University in Japan, said:

The study is part of Reinhard’s research goal to understand how the evolution of the photosynthetic biosphere controlled the composition of Earth’s atmosphere, Reinhard said:

Ozaki explained:

Reinhard added that the results:

Other authors of the study are Katharine Thompson, Rachel Simister, and Sean Crowe of the University of British Columbia.

Provided by: Maureen Rouhi,  [Note: Materials may be edited for content and length.]

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