In the first 2 billion years of Earth's history, there was hardly any oxygen in the air. Although some microbes were photosynthesizing in the latter part of this period, oxygen had not yet reached the level that would affect the global biosphere.
But about 2.3 billion years ago, this stable, low-oxygen balance changed, and oxygen began to accumulate in the atmosphere, finally reaching the level necessary for the life we breathe today. This rapid infusion is known as the Great Oxygen Event or GOE. What triggered this phenomenon and brought the planet out of its low oxygen level is one of the great mysteries of science.
A new hypothesis proposed by MIT scientists suggests that due to the interaction between certain marine microbes and minerals in ocean sediments, oxygen eventually began to accumulate in the atmosphere. These interactions helped prevent oxygen from being used, which triggered a self-promoting process in which more and more oxygen was available to accumulate in the atmosphere.
Scientists have presented their hypothesis using mathematical and evolutionary analyzes, which show that microbes actually existed before GOE and developed the ability to interact with sediment in the ways researchers have suggested.
His study, published in Nature Communications, is the first to link the combined evolution of microbes and minerals to the Earth's oxygen.
Probably the most important biogeochemical change in the history of the planet was the oxygenation of the atmosphere, says study author Daniel Rothman, who specializes in geophysics at MIT's Department of Earth, Atmospheric and Planetary Sciences EAPS. Are professors, We explain how the interaction of microbes minerals and biochemicals worked in concert to increase the oxygen in the atmosphere.
Co-authors of the study include lead author Haitao Shang, a former MIT graduate student, and Gregory Fournier, an associate professor of geobiology at EAPS.
A step up
The current level of oxygen in the atmosphere is a stable balance between the oxygen-producing process and its users. Prior to GOE, the atmosphere maintained a variety of balances, with oxygen producers and consumers in balance, but did not release much oxygen to the atmosphere.
What could push the planet from one stable, oxygen-deficient state to another stable, oxygen-rich state?
If you look at the history of the Earth, it looks like there were two leaps, where you went from a stable state of low oxygen to a very high level of oxygen, once in a paleoproterozoic, once in a neoproterozoic, he says. Fournier .. These leaps cannot be due to a gradual increase in extra oxygen. There must be some feedback loop that led to this fundamental change in stability.
He and his colleagues wondered if such a positive feedback loop could come from a process at sea that did not make some organic carbon available to its consumers. Organic carbon is used primarily by oxidation, usually with oxygen consumption, a process by which microorganisms in the oceans use oxygen to break down organic matter, such as detritus, which is present in sediments. Are settled. The team thought: Could there be a process by which the presence of oxygen stimulates its further accumulation?
Shang and Ruthman devised a mathematical model that predicted the following: If microbes are capable of partially oxidizing organic matter, partially oxidized matter, or "POOM", effectively "sticky" and Will be chemically attached to minerals. The method that protects the material from further oxidation. Oxygen that would otherwise be used to completely degrade the material would be released into the atmosphere. They found that the process could act as a positive feedback, providing a natural pump to push the atmosphere towards a new high oxygen balance.
"It forces us to ask, is there any microbial metabolism that produces POOM?" Says Foyer.
In the genes
To answer this, the team searched the scientific literature and identified a group of microbes that today partially oxidize organic matter in the deep sea. These microbes belong to the SAR202 bacterial group, and are partially oxidized by an enzyme, Baeyer-Villiger monooxygenase or BVMO.
The team performed a phylogenetic analysis to determine how far behind the germs and genes for the enzyme. They found that the ancestors of bacteria existed before GOE, and that the enzyme gene could be traced back to various microbial species even before GOE.
Furthermore, they found that gene diversity, or the number of species that receive the gene, increased significantly when there was an increase in oxygen in the atmosphere, including once during GOE's Paleoproterozoic and then in Neoproterozoic.
We found a temporary link between the genes that make up POOM and the diversity of oxygen levels in the atmosphere, says Shang.
This assumption would require a lot of follow-up, from lab experiments to field surveys, and everything in between. With their new study the team has introduced a new suspect in the old case of providing oxygen to the Earth's atmosphere.
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