The End-Triassic Mass ExtinctionSince the start of life with hard parts, there are 5 known major “ma

The End-Triassic Mass ExtinctionSince the start of life with hard parts, there are 5 known major “mass extinctions” where large fractions of the species and higher order taxa on this planet went extinct in short order. Two of these are fairly well understood – the Cretaceous/Paleogene mass extinction was triggered by an asteroid impact, and the Permian/Triassic mass extinction was triggered by events occurring during gigantic volcanic eruptions in modern-day Siberia. The extinction in-between those events, at the boundary between the Triassic and Jurassic, is less well understood.Like the end-Permian, the end-Triassic mass extinction overlaps with the emplacement of a large volcanic province, this one known as the Central Atlantic Magmatic Province (CAMP). These lavas are found throughout North America, Africa, and into South America, and the plume that led to their formation likely was a major factor in triggering the opening of the modern day Atlantic Ocean.The end-Permian mass extinction is thought to have been triggered specifically because the magmas interacted with a large coal deposit, dramatically altering their chemistry. While the CAMP is large, scientists are still working to understand how it could have triggered large numbers of extinctions. In general, it is thought that the most likely cause is a combination of rapid global temperature increase, triggered by release of CO2 due to the eruptions of the volcanic rocks on land, and dramatic changes in the ocean chemistry, including loss of oxygen that would create global dead zones.This image shows 3 sampling sites for sediments taken from the 2 great portions of the Triassic ocean, the Tethys seaway and Panthalassa. To investigate the amount of oxygen in the oceans at the time, a team of scientists led by a researcher at the University of Leeds sampled these sites and investigated the sulfur chemistry and isotopes in the rocks at the time. Sulfur should have a strong response to the availability of oxygen – if the waters are oxidized, sulfur will be found as sulfate, while waters that are missing oxygen will form reduced sediments that contain pyrite. Furthermore, sulfur has several stable isotopes that preferentially go into the oxidized and reduced forms of sulfur, so measuring isotope ratios of sulfur is a powerful way to hunt for evidence of low-oxygen oceans.Under normal ocean conditions, one way that oxygen remains in the deep ocean is a process involving sulfur. Bacteria that process sulfur use up organic carbon, so the organic carbon never reacts with oxygen in the water. If this process shut down, carbon would build up in the ocean deep water, use up the oxygen, and trigger expansion of dead zones. That’s exactly what the scientists propose; they see a big spike in pyrite formation just before the mass extinction, suggesting sulfur was being removed from the ocean and dead zones were growing. Then, when the warming spike from the volcanism occurred, it found an ocean that was already unstable; a little push of increased temperature drove away the last bits of oxygen, causing widespread dead zones globally that could contribute to the mass extinction.-JBBImage credit and original paper:https://advances.sciencemag.org/content/6/37/eabb6704 -- source link

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