Oxygen was scarce in the atmosphere for the first two billion years of Earth's history. Even while some microbes were already capable of photosynthesis by the end of that time period, the oxygen generated by these organisms was insufficient to have a worldwide influence.
About 2.3 billion years ago, the atmosphere began to build up vast amounts of oxygen, allowing life on Earth to flourish as we know it. A "Great Oxygenation Event" (GOE) is known to scientists, but what exactly caused it remains one of science's greatest mysteries.
New research from the Massachusetts Institute of Technology (MIT) suggests that oxygen could begin to collect in ocean sediments due to interactions between marine bacteria and minerals in the sediment. To put it another way, these interactions assisted to keep oxygen from being depleted, which resulted in an increase in the amount that could be released into the atmosphere, as reported in the journal Nature Communications.
For the first time, researchers have linked the evolution of bacteria and minerals to the Great Oxygenation Event (GOE). The researchers found that bacteria existed before to the big oxygenation, and that those microbes evolved the ability to interact with sediments in the hypothesized manner.
The oxygenation of the atmosphere was perhaps the most significant biogeochemical alteration in the history of the planet, according to the article's lead author, Daniel Rothman. We demonstrate how microbial, mineral, and geochemical interactions contributed to the increase in atmospheric oxygen concentration.
From one kilo to the next
There is a stable equilibrium between the mechanisms that produce oxygen and those that consume it at present's levels of atmospheric ozone. For a long time before GOE, the atmosphere was in a state of equilibrium, with a balance between the production and consumption of oxygen, but this balance left little additional oxygen for the atmosphere. How did the earth go from a stable, oxygen-starved state to a stable, oxygen-rich state?
"If you look at Earth's history, says Gregory Fournier, co-author of the study, it appears that there were two jumps, one in the Paleoproterozoic and again in the Neoproterozoic, in which it shifted from a stable condition of little oxygen to a stable state of substantially more oxygen. A slow buildup of extra oxygen cannot account for these jumps. A feedback loop has to have been involved in this sudden shift in stability.
A positive feedback loop may be created if a process in the water made some organic carbon unavailable to its users, researchers speculated. When marine bacteria use oxygen to break down organic matter, oxidation takes place, which results in a loss of organic carbon. As a result, the research team began to question if oxygen itself was somehow stimulating further accumulation.
A mathematical model developed by the study's authors predicted the following result: This "sticky" organic substance, known as "POOM," may be created by microorganisms if they could only partially oxidize organic materials. safeguard minerals from further oxidation by binding them chemically. As a result, oxygen that would have otherwise been wasted in the process of degrading the substance is now available to build up in the environment. Scientists have discovered a natural pump that can drive the atmosphere into a new high-oxygen equilibrium as a result of this mechanism.
That led us to question if there was some natural mechanism that may make POOM (partially oxidized matter)," Fourier continued.
The answer to one inquiry raises many.
For the new inquiry, researchers investigated the scientific literature and discovered a group of bacteria in the deep ocean that only partially metabolize organic materials. The Baeyer-Villiger monooxygenase or BVMO enzyme is responsible for the partial oxidation of these microorganisms, which belong to the SAR202 bacterial group.
According to the researchers, they discovered that these bacteria had ancestors before GOE, as well as traced the enzyme gene through various microbial species, even before the Great Oxygenation Event (GOE). When the atmosphere experienced oxygenation spikes, scientists discovered significant gene diversification—the number of species that inherited a gene—in both the Paleoproterozoic and the Neoproperosauric periods. The temporary link had been established.
Author Haitao Shang says, "We identified some temporal relationships between POOM gene diversity and atmospheric oxygen levels." He's quoting himself. So our general premise holds up," he adds.
There is still a lot of work that needs to be done to confirm this hypothesis, from laboratory experiments to in-the-field studies. New evidence has been found to support the long-standing theory of increased oxygenation in the atmosphere.
"The first but crucial step is to propose a novel method and show evidence of its plausibility," says Fournier. "We have demonstrated that this is a notion that deserves further investigation."
