The deadliest period in Earth’s history was also the stinkiest


Tiny, poisonous gas-spitting microbes helped cause – and prolong – the largest mass extinction in Earth’s history, a new study suggests.

The volcanoes of present-day Siberia triggered the world’s largest mass extinction event.

Typically, scientists believe that greenhouse gas-spitting Siberian volcanoes primarily caused mass extinction around 250 million years ago, at the end of the Permian period. The gases caused extreme warming, which in turn led to the extinction of 80% of all marine species, as well as many terrestrial species.

Until now, scientists couldn’t explain exactly how the heat caused these deaths. A new study by UC Riverside in Nature Geoscience shows that heat accelerated the metabolism of microbes, creating deadly conditions.

“After oxygen from the ocean was used to break down organic matter, the microbes began to ‘breathe’ sulfate and produced hydrogen sulfide, a gas that smells like rotten eggs and is toxic to animals, ”said Dominik Hülse, modeler of the UC Riverside Earth system.

As ocean photosynthesizers – the microbes and plants that form the base of the food chain – decayed, other microbes quickly consumed oxygen and left little for larger organisms. In the absence of oxygen, the microbes consumed sulfate and then expelled poisonous, smelly hydrogen sulfide, or H2S, creating an even more extreme condition called Ilsinia. These conditions were maintained by the release of nutrients during decomposition, promoting the production of more organic matter which helped maintain this toxic and stinky cycle.

“Our research shows that the entire ocean was not theminic. These conditions started in the deepest parts of the water column, ”said Hülse. “As temperatures increased, the areas of the Venus became larger, more toxic, and moved up the water column to the plateau environment where most of the marine animals lived, poisoning them. ”

Expanding theminic zones can be detected by chemical signatures in sediment samples.

H2S reaction, nose holding
Dominik Hülse, modeler of the UC Riverside Earth system reacting with hydrogen sulphate. (Dominik Hülse / UCR)

Oxygen depletion is a problem that persists today and is sure to worsen with future climate change. Censinic waters can be found in places like the 16-mile-long Dominguez Canal in Los Angeles County, where a warehouse fire in September 2021 released ethanol. The ethanol killed the vegetation in the canal, which decomposed and was consumed by the microbes. They then produced hydrogen sulfide at toxic levels. Thousands of people in the stinking river breathing zone have reported vomiting, diarrhea, dizziness, insomnia, headaches, sneezing and other symptoms.

Lessons from the ancient world can be important in understanding the processes that challenge our modern oceans and waterways.

“It would be speculative to superimpose the ancient event of mass extinction on today’s planet,” Hülse said. “However, the study shows us that the ocean’s response to higher concentrations of carbon dioxide in the atmosphere may be underestimated.”


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