We may have microbes and minerals to pay tribute to Earth's Oxygenation-Rich Atmosphere

We may have microbes and minerals to pay tribute to Earth's Oxygenation-Rich Atmosphere ...

For the first two billion years of Earths history, there was barely any oxygen in the air. While some microbes were photosynthesizing by this period, oxygen had not yet accumulated at levels that would affect the global biosphere.

This stable, low-oxygen equilibrium shifted 2.3 billion years ago, and oxygen began building up in the atmosphere, eventually reaching the life-sustaining levels we breathe today. This rapid infusion is known as the Great Oxygenation Event, or GOE. What triggered the event and repelled the planet out of its low-oxygen funk is one of the greatest mysteries of science.

A new myth, established by MIT scientists, claims that oxygen eventually became accumulating in the atmosphere due to interactions between certain marine microbes and minerals in ocean sediments. These interactions helped prevent oxygen from being consumed, putting off a self-amplifying process where more and more oxygen was given to accumulate in the atmosphere.

The scientists have constructed their hypothesis using mathematical and evolutionary methods, indicating that there were effective microbes that existed before the GOE and enhanced the capacity to interact with sediment in the manner they have proposed.

Their research, which is today on Nature Communications, is the first to transact microbes and minerals'' co-evolution to Earth''s oxygenation.

According to study author Daniel Rothman, the atmosphere''s most significant biogeochemical change, was oxygenation. During the session, microbes, minerals, and the geochemical environment acted in concert in order to increase oxygen availability.

The authors of these studies include lead author Haitao Shang, a former MIT graduate student, and Gregory Fournier, an associate professor of geobiology at EAPS.

A step up

Heavily, oxygen levels in the atmosphere are a healthy balance between the processes that produce oxygen and those that consummate it. Prior to the GOE, the atmosphere maintained a different kind of equilibrium, with producers and consumers of oxygen in sync, but in a way that didn''t leave much additional oxygen for the atmosphere.

What might have been pushed the planet out of one stable, oxygen-deficient state?

If you look at Earths history, it appears there were two jumps, where you advanced from a steady state of low oxygen to a steady state of much higher oxygen, once in the Paleoproterozoic, once in the Neoproterozoic. These jumps couldnt have been attributed to a gradual increase in excess oxygen. This process-change in stability had to be successful.

He and his colleagues wondered if such a positive feedback loop might have been due to a process in the ocean that rendered organic carbon unavailable to its customers. Organic carbon is mainly consumed through oxidation, usually accompanied by the consumption of oxygen, a process by which microbes in the ocean use oxygen to break down organic matter, such as the damage that has settled in sediments. The team wondered: Could there have been any process by which the presence of oxygen had boosted its further accumulation?

Microbes possessed the ability to only partially oxidize organic matter, and the partially-oxidized matter, or POOM, would effectively become sticky and chemically binding to minerals in sediment in a manner that would minimize further oxidation. This process, according to Shang and Rothman, might provide a positive feedback, fostering the atmosphere in a new high-oxygen equilibrium.

Is there a microbial metabolism out there that sparked POOM? Fourier says.

In the genes

A team of researchers identified a group of microbes that partially oxidize organic matter in the deep ocean today. These microbes belong to the bacteria group SAR202, and their partial oxidation is conducted by an enzyme, Baeyer-Villiger monooxygenase, or BVMO.

A phylogenetic analysis was carried out to determine how far back the microbe and the enzyme gene could be traced. They found that the bacteria had indeed existed before the GOE, and that the gene for the enzyme could be traced across several microbes as far back as pre-GOE times.

Moreover, they found that genes diversification, or the number of individuals who acquired the gene, increased significantly during times when the atmosphere experienced increased oxygenation, including once during the GOEs Paleoproterozoic, and once in the Neoproterozoic.

We discovered some temporal connections between the diversification of POOM-producing genes and the oxygen levels in the atmosphere, according to Shang. That is the basis for our overall understanding.

To confirm this hypothesis, the process of conducting experiments in the lab will require far greater follow-up, from surveys in the field to anything in between. With their latest discovery, the team has identified a new clue in the ancient Earths atmosphere.

Proposing a new approach and demonstrating its plausibility is the first but important step, according to Fournier. Weve identified this as a possibility worthy of study.

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