Single-cell organism could have caused Earth's worst mass extinction: scientists have evidence

Dmytro IvancheskulLife
The root cause of the greatest extinction on Earth may have been microbes

If you ask a random person about extinctions on Earth, they will probably think of the asteroid that hit the planet and wiped out all the dinosaurs. The so-called Cretaceous-Paleogene extinction, which occurred about 66 million years ago, was indeed massive, but not the largest in history. The Permian Mass Extinction is also known as "the greatest mass extinction of all time" for a reason and it is quite possible that a tiny organism was the cause.

This is the theory of the Massachusetts Institute of Technology (MIT), the essence of which is told by the publication IFLScience. The Permian mass extinction wiped out about 70% of all terrestrial species and 96% of all marine species on Earth.

There are different theories as to the causes that led to this event: from a catastrophic release of methane from the ocean floor to an asteroid impact.

Researchers know that at the end of the Permian period, there was a lack of oxygen in the oceans and shallow waters. This had a significant role in the extinction of species and also caused a domino effect.

The lack of oxygen probably led to the flourishing of sulfate-reducing microorganisms, which use sulfates rather than oxygen for respiration. In the process, these microorganisms produced a byproduct, hydrogen sulfide, and triggered the sulfidization of the oceans. This in turn affected the atmosphere, causing poisoning of plants and damage to the ozone layer, exposing life to the deadly ultraviolet rays of the sun, and heating the planet in the process. When the oceans warmed up, this caused frozen methane to be released into the atmosphere and further exacerbated the problem.

However, scientists from MIT have a different explanation for those events, and their theory is troubling. Microbes were probably the root cause of the greatest extinction on Earth.

Daniel Rothman, a geophysics professor at MIT, said that he and his team discovered an increase in the population of a certain microbe around the same time that the extinction was occurring.

The single-cell organism Methanosarcina became capable of digesting organic matter, producing methane as a byproduct. It gained this ability through a single gene transfer from the bacterium Clostridia.

The scientists' hypothesis suggests that Methanosarcina thrived by releasing methane into the atmosphere, causing destruction or disrupting the carbon cycle and eventually leading to species extinction.

As proof of their theory, the scientists revealed that the chemical process involved in the microbes making methane involves the metal nickel. When scientists examined the most studied sediments in southern China, this is what they found.

The study authors suggested that a single gene transfer "triggered biogeochemical changes, massive volcanism acted as a catalyst, and the expansion of acetoclastic methanesarcina led to increased CO2 and O2 levels.

"The resulting biogeochemical disturbances would likely have been widespread. For example, anaerobic oxidation of methane could have led to increased sulfide levels, possibly leading to toxic release of hydrogen sulfide into the atmosphere, causing extinction of species on land," the scientists told us.

They acknowledge that while more evidence is needed to confirm this theory, the study showed how sensitive the Earth is to the evolution of microbial life.

"The implications for the present are that there are many ways in which natural fluctuations can occur in the Earth's carbon cycle. As we study the changes now happening to the carbon cycle, we should try to account for as many of them as possible to make future predictions," he said. Rothman.

The study is still far from a definitive conclusion, as it is possible that the mass extinction was caused by several factors and it is also impossible to determine exactly when Methanosarcina evolved to start producing methane.

However, if the hypothesis is correct, it is possible that up to 90% of the species on the planet were partially exterminated by a single gene transfer in a single microorganism and this begs the question when you consider the sheer number of microbes on Earth.

Earlier OBOZREVATEL also told the forecast of scientists about what can expect mankind in case of awakening of zombie bacteria buried in permafrost.

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