Stratigraphy and sulfur isotopes for the Meishan section, China, across the Permian-Triassic boundary. Credit: Li et al. 2024.
The concept of deadly mass extinctions that caused the destruction of Earth’s ecosystems millions of years ago has fascinated the public and scientists for decades.
A groundbreaking publication by Jack Sepkoski and David Raup in 1982 identified the “big five” extinction events throughout the planet’s geological history, these being defined as the end of the Ordovician (~444 years ago at 445 million years ago, Ma), the Upper Devonian (~ 359 to 359 million years ago). 372 Ma), late-Permian (~252 Ma), late-Triassic (~201 Ma) and late-Cretaceous (~66 Ma). The end-Permian event is considered the most important of these biotic crises.
During this catastrophe, it is estimated that approximately 81% of all marine species and approximately 70% of terrestrial vertebrate species became extinct. But the event did not only affect animals: land plants also suffered significant mutations and destruction.
Explosive volcanism in the large igneous province of Siberia, covering approximately 7,000,000 km2, is evidenced by massive deposits of pyroclastic flows and is postulated to be the most likely trigger of the end-Permian mass extinction. This has caused a range of adverse effects, such as ocean anoxia, hydrogen sulfide poisoning, acid rain, ozone depletion and global warming.
New research published in Chemical Geology studied the link between ozone-damaging volcanism and increased irradiation of the Earth, thereby leading to a plethora of irreversible changes across the planet.
Dr. Rucao Li, a postdoctoral researcher at Nanjing University, China, and colleagues studied pyrite from the ash layers of the Meishan section in southern China to measure sulfur isotopes and understand the The effect of sulfur dioxide emissions from volcanoes on stratospheric ozone.
Schematic explanation of the relationship between volcanism penetrating the stratosphere and the consequences leading to the end-Permian mass extinction. A) During the Permian, an ozone layer protected the planet from incoming solar radiation. B) Explosive volcanic eruptions introduced sulfur dioxide and other molecules into the stratosphere, which disrupted the ozone layer, causing sulfur dioxide to photolyze to produce MIF-S sulfate aerosols that were transported to the ocean and underwent chemical reactions to produce hydrogen sulfide, making the water column sulfuric and anoxic. C) After the eruption, the ozone layer was not restored and prolonged UV irradiation damaged terrestrial and marine flora and fauna beyond their survival. Credit: Li et al. 2024.
To do this, the research team used secondary ion mass spectrometry to detect the presence of three isotopes of sulfur (sulfur-33, sulfur-34 and sulfur-36) in microscopic grains of pyrite (10 to 30 µm).
Scientists identified a distinct positive change of +0.30‰ to +0.94‰ in mass-independent fractionation sulfur isotopes (MIF-S) in a bed of the study section located a few centimeters below of the designated late Permian bed, where there is a coincidental increase in the abundance of ash layers. However, in the bed called the Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary, there is no distinct MIF-S signal.
Dr. Li and his colleagues note that such a large change has rarely been seen in rocks less than 2 billion years old due to the gradual increase in the planet’s oxygen budget and the formation of ozone over time, which ultimately impacted sulfur oxidation.
The process by which volcanic emissions may have led to this planetary catastrophe is linked to the photolysis (degradation of molecules due to the absorption of light) of sulfur dioxide by ultraviolet radiation.
Once the explosive volcanism disrupted the ozone layer and entered the stratosphere, there would have been fewer oxygen molecules blocking incoming solar ultraviolet radiation, leading to the conversion of sulfur dioxide molecules into sulfate aerosols MIF-S, which were transported from land to the oceans. This has indeed been corroborated by modeling suggesting a 30% decrease in atmospheric oxygen in the Phanerozoic (early ~538 Ma) to half of this level at the end of the Permian.
Dr. Li and colleagues suggest that sulfate-reducing bacteria in the ocean then convert the MIF-S-preserving molecules into hydrogen sulfide, rendering the marine world both sulfidic and anoxic, a catastrophic combination for survival. . With terrestrial organisms exposed to high-intensity ultraviolet radiation on land and oxygen producers in the shallow photic zone of the sea negatively affected, this would have filtered through the water column as the oxygen supply decreased. Ultimately, there was no escape on Earth from the harmful effects of ozone destruction.
Although not as devastating, concerns over ozone depletion in recent decades have very real consequences for our planet’s terrestrial and marine organisms, as well as humans.
More information:
Rucao Li et al, Atmospheric ozone destruction and the end-Permian crisis: evidence from multiple sulfur isotopes, Chemical Geology (2024). DOI: 10.1016/j.chemgeo.2024.121936
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Quote: Volcanism-induced ozone depletion may have contributed to the Permian mass extinction, according to a study (February 12, 2024) retrieved February 12, 2024 from
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