Volcanic eruptions millions of years apart wiped out much of life on Earth.

Massive volcanic eruptions millions of years apart caused two mass extinctions during the Middle Permian period, according to a study of uranium isotope profiles in marine samples. The findings highlight the potential effects of modern global warming on ocean food webs and the importance of addressing environmental issues to prevent further extinctions.

Long before the dinosaurs, the Earth was dominated by animals that were in many ways even more amazing.

Carnivores such as Titanophoneus, or “titanic killer”, stalked huge armored reptiles the size of buffalo.

Many of these animals died out in a mass extinction during the Captainian era, around 260 million years ago.

Now, an international team of researchers says evidence suggests this mass extinction was not a single event but two, separated by nearly 3 million years. Both were caused by the same culprit: massive volcanic eruptions.

By studying the uranium isotopic profiles of marine samples taken from the South China Sea, scientists have identified two “pulses” in which the oceans were deprived of vital oxygen.

In a study published in the journal Earth and Planetary Science Lettersthe researchers say their analysis provides evidence that oxygen-deprived oceans precipitated two mass extinctions around 259 million and 262 million years ago during the Middle Permian period.

Imminent climate catastrophe

By studying these ancient extinctions, researchers can better predict how current global warming might affect the ocean’s food web.

“We study biocrisis in the Permian period, but similar warming is happening today due to human events,” said Thomas Algeo, study co-author and professor of geosciences at the University of Cincinnati ( CPU). “Humans mimic the effects of volcanic eruptions due to the release of carbon into the atmosphere.”

The study was led by China University of Geosciences researcher Huyue Song, a former postdoctoral researcher at UC.

“Today we are facing several climate change issues, including global warming, ocean hypoxia, seawater acidification and biodiversity decline, which are similar to environmental changes during of the Middle Permian Biological Crisis Interval,” Song said.

Scientists have identified the five largest mass extinctions, including the most cataclysmic of all 252 million years ago called “the great death” which wiped out 90% of ocean life and 70% of land animals. This disaster was also caused by massive volcanic activity that turned the seas into dead zones, Algeo said.

“The Capitanian extinctions aren’t one of the Big Five, but they are significant,” Algeo said.

How do volcanic eruptions lead to extinctions?

Algeo said the massive eruptions create a brief period of cooling from ash in the upper atmosphere reflecting sunlight, followed by much longer periods of global warming. The release of massive volumes of greenhouse gases has warmed the oceans. The warm surface water did not allow dissolved oxygen to reach lower depths, ultimately destroying the food chain.

“The ocean is on the brink of anoxia,” he said of this lack of oxygen. “Dissolved oxygen has to be taken up by the surface layer and supplied to the deep ocean. But warmer water has a lower density. When you increase the density differential, you prevent any overturning and there is no no way to get dissolved oxygen into the deeper layers.

Researchers identify these massive volcanic eruptions by looking for mercury in sedimentary layers.

“Mercury has proven to be a useful proxy for volcanic eruptions,” Algeo said. “Large volcanic eruptions release mercury into the atmosphere which is transported around the Earth and deposited in marine sediments.”

Scientists say the volcanic eruptions that caused the great death originated in Siberia. The eruptions that caused the twin Permian mass extinctions took place in southwestern China in a place known as the Emeishan Great Igneous Province.

“Over the past 40 years, we have made enormous strides in understanding Earth’s past.” — Thomas Algeo, UC College of Arts and Sciences

Algeo said he would like to see if any terrestrial evidence supports the conclusions drawn from their study of ancient oceans. He is optimistic that geology will reveal more mysteries about prehistoric life on Earth.

“Over the past 40 years, we’ve made tremendous progress in understanding Earth’s past,” Algeo said. “It’s partly because we have all these new tools that we can apply. And we have many more people working in this area than a generation ago.

Researcher Song said the Permian twin catastrophes show the devastating effects that global warming can have.

“We need to pay attention to these environmental issues and prevent the sixth mass extinction,” he said.

Reference: “Global ocean anoxia linked to the Capitanian (Middle Permian) marine mass extinction” by Huyue Song, Thomas J. Algeo, Haijun Song, Jinnan Tong, Paul B. Wignall, David PG Bond, Wang Zheng, Xinming Chen, Stephen J Romaniello, Hengye Wei, and Ariel D. Anbar, March 30, 2023, Earth and Planetary Science Letters.
DOI: 10.1016/j.epsl.2023.118128