Scientists propose a new mechanism by which oxygen may have first built up in the atmosphere

There was barely any oxygen in the air for the first 2 billion years of Earth's history. Oxygen had not yet been accumulated at levels that would impact the global biosphere, as some microbes were photosynthesizing by the last part of this period.

Oxygen began building up in the atmosphere around 2.3 billion years ago when the stable, low-oxygen equilibrium shifted. The Great Oxygenation event is a rapid infusion. One of the great mysteries of science is what triggered the event that pulled the planet out of its low-oxygen state.

MIT scientists have proposed a new hypothesis that suggests that oxygen finally started accumulating in the atmosphere thanks to interactions between certain marine microbes and minerals. The interactions helped prevent oxygen from being consumed, setting off a self-amplifying process where more and more oxygen was made available to accumulate in the atmosphere.

The scientists used mathematical and evolutionary analyses to show that there wereMicrobes that existed before the GOE and that they evolved the ability to interact with sediment.

Their study is the first to link the evolution of minerals and microbes to Earth's oxygenation.

Oxygenation of the atmosphere was the most important biogeochemical change in the history of the planet, according to study author Daniel Rothman, professor of geophysics in MIT's Department of Earth, Atmospheric, and Planetary Sciences (EAPS).

The lead author of the study is a former MIT graduate student.

A step up.

Oxygen levels in the atmosphere are stable because of processes that produce and those that consume it. Prior to the GOE, the atmosphere had a different kind of equilibrium, with producers and consumers of oxygen in balance, but not much extra oxygen for the atmosphere.

What could have caused the planet to go from being oxygen deficient to being oxygen rich?

If you look at Earth's history, you can see that there were two jumps, one in the Paleoproterozoic and the other in the Neoproterozoic. There had to have been a feedback loop that caused this step change.

He and his colleagues wondered if the positive feedback loop could have come from a process in the ocean that made some organic carbon unavailable to its consumers. Oxygen and oxidation are the two main ways in which organic carbon is consumed. The team wondered if there was a process by which the presence of oxygen stimulated its further accumulation.

The mathematical model that was worked out was that if the microbes had the ability to only partially oxidize organic matter, the partially-oxidized matter would become sticky and bind to something. Oxygen that would have been used to degrade the material would be free to build up in the atmosphere. They found that this process could serve as a positive feedback, providing a natural pump to push the atmosphere into a high-oxygen equilibrium.

"That led us to ask, is there a microbial metabolism out there that produced POOM?"

In the genes.

The team searched through the scientific literature and found a group of microbes that oxidizes organic matter in the deep ocean. The partial oxidation of these microbes is carried out through anidase called Baeyer-villiger monooxygenase.

To find out how far back the microbe is, the team used a phylogenetic analysis. They found that the genes for the enzyme could be traced back to pre- GOE times, and that the ancestors of thebacteria were present before the GOE.

During times when the atmosphere experienced spikes in oxygenation, the number of species that acquired the gene increased significantly.

The correlation between the oxygen levels in the atmosphere and the POOM- producing genes was found.

It will take far more follow-up to confirm this hypothesis, from experiments in the lab to surveys in the field. The team has introduced a new suspect in the age-old case of what oxygenated Earth's atmosphere.

Fournier says that the first step is to show evidence for a novel method.

More information: Oxidative metabolisms catalyzed Earth's oxygenation, Nature Communications (2022). Journal information: Nature Communications Citation: Scientists propose a new mechanism by which oxygen may have first built up in the atmosphere (2022, March 14) retrieved 14 March 2022 from https://phys.org/news/2022-03-scientists-mechanism-oxygen-built-atmosphere.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.