When you think of a major extinction event, the first thing that comes to mind is the asteroid that killed the dinosaurs. But Earth has experienced (so far) five mass extinctions, and we’re experiencing a sixth, according to some claims.
The Cretaceous mass extinction event that ended the non-avian dinosaurs is not the largest of all extinction events. That honor goes to the Permian mass extinction, the Great Dying, that wiped out about 90 percent of all land species on Earth and 70 percent of all marine species.
In addition, a strange 10-million-year gap in coal during extinction, known as the “coal gap”, indicates that many coal-forming trees were exhausted during the event and took millions of years to recover.
It turns out, finding a time period in the fossil record where there was a sudden drop in species numbers is the easy part. Scientists offer many different explanations for the extinction and the reasons behind it, from a massive release of methane from the ocean floor to an asteroid impact.
Thanks to research on rocks formed during extinction, we know that the oceans and shallow waters were oxygen-free during the late Permian. The lack of oxygen (i.e. anoxia) seems to have played a role in the extinction, as well as having a knock-on effect.
Sulfate-reducing microorganisms, which can perform anaerobic respiration using sulfate instead of oxygen, were probably quite widespread in these low-oxygen environments. These gases may have been released into the atmosphere, as well as the hydrogen sulfide byproduct they produce making the oceans acidic with sulfur. Here it may have poisoned plants and damaged the ozone layer, exposing life to lethal levels of UV rays, while warming the planet in the process. On the other hand, the warming of the oceans may have exacerbated the problem by causing the frozen methane gas in the oceans to be released into the atmosphere.
An alternative explanation for extinction, proposed by a team from MIT in 2014, is perhaps the most worrying. According to this suggestion, microbes could be the cause of the biggest extinction event the Earth has ever seen.
Daniel Rothman, Professor of Geophysics at MIT, and his team noticed the rise of a particular microbe at times of extinction. Methanosarcina, a single-celled organism, was able to produce methane as a byproduct by digesting organic matter, thanks to a single gene transfer from the bacterium Clostridia.
The hypothesis is that Methanosarcina grew during this period, spewing methane into the atmosphere, causing (or contributing to) disruption of the carbon cycle, and ultimately fueling the extinction event.
The chemical process by methane-forming microbes involves the metal nickel. So if the team does not find a correspondingly higher amount of nickel during the extinction event, the hypothesis can effectively be dismissed. However, the team did find high nickel levels in the most studied sediments in southern China, which seemed to support the hypothesis.
“A single horizontal gene transfer triggered biogeochemical change, massive volcanism acted as a catalyst, and the resulting expansion of acetoclastic Methanosarcina acted to disrupt CO2 and O2 levels,” the team continues. would be. For example, anaerobic methane oxidation can increase sulfide levels, possibly resulting in a toxic release of hydrogen sulfide into the atmosphere and causing land extinctions.”
The study draws attention as a still imprecise suggestion, with other explanations or perhaps a combination of events. It’s also not possible to pinpoint exactly when Methanosarcina evolved to start producing methane as a byproduct. If this hypothesis is correct, it would mean that it’s possible that up to 90 percent of species on the planet were partially wiped out by a single gene transfer in a single microbe.
Given the amount of microbes in the world, we can say that this is probably one of the scariest prospects we’ll ever hear.
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