Researchers at the Massachusetts Institute of Technology (MIT) have proposed a new theory to explain how oxygen concentration might have built up in the Earth’s atmosphere, according to a press release.
Billions of years before humans were born, the Earth’s atmosphere lacked the oxygen we need to survive. Some microbial organisms use photosynthesis to generate some oxygen; However, the quantities produced were not sufficient to sustain many life forms. However, about 2.3 billion years ago, oxygen level began to build up in the atmosphere, but the reasons for this are still unknown.
Great oxygenation event
Early in Earth’s history, the planet’s oxygen producers & consumers maintained a balance in such a way that there was little oxygen left in the atmosphere. However, there were 2 events in the Paleoproterozoic period and the Neoproterozoic period, which saw oxygen levels rise from low levels to much higher levels than Earth has today.
Gregory Fournier, associate professor of geobiology in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS), and colleagues believe these jumps in oxygen levels were not the result of a gradual change. Instead, there was positive feedback Loop that was activated in oceans.
According to Fournier and his team, organic carbon, whose break-down under normal circumstances consumes oxygen (also called oxidation), was likely unavailable to its consumers during those intervals that led to oxygen enrichment. Since life existed in the oceans, the researchers studied microbes & minerals in ocean sediments to see if such a situation could occur.
They hypothesized that if microbes in these environments were able to partially oxidize organic matter, partially oxidized organic matter (POOM) would bind to minerals in a way that prevented their further oxidation. Oxygen not used in the process would end-up in atmosphere.
Microorganism we need to thank
To test their hypothesis, the researchers scoured the scientific literature to identify microorganisms that could create POOMs & found a bacterial group called SAR202 that can accomplish the feat using an enzyme called Baeyer-Villiger monooxygenase, or simply BVMO.
By tracing the genetic origins of this enzyme, the researchers discovered that the bacteria’s ancestors were present long before GOE. Interestingly, the gene was acquired from several bacterial species during Paleoproterozoic & Neoproterozoic, times when oxygen levels are known to spike.
While these correlations provide support to new theory, researchers need to-do extensive work to do to figure out what it takes to prove it.
The mystery of the GOE may have just begun to unfold.
The findings are published in the journal Nature Communications.