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Triassic Mass Extinction

An analysis of biomarkers and their stable isotopic compositions from the Bristol Channel Basin at St. Audrie’s Bay and Lilstock, United Kingdom, has shed new light on when one of the largest mass extinction events on Earth occurred.

Schematic diagram showing the factors driving global ecological change in the modern day and at the end of the Triassic period. Image credit: Victor Lesh.

Schematic diagram showing the factors driving global ecological change in the modern day and at the end of the Triassic period. Image credit: Victor Lesh.

Most of the major mass extinctions of the last 300 million years, as well as some of the lesser biotic turnover events, are associated with reorganizations or perturbations of the Earth’s natural carbon cycle.

The end-Triassic mass extinction began after a volcanic eruption spewed carbon dioxide into the atmosphere, disrupting the carbon cycle and sparking a chain reaction of environmental events.

That carbon disruption led to acidic ocean waters which then affected delicate marine ecosystems, and led to other unfavorable planetary changes.

The extinction event resulted in the demise of some 76% of all marine and land species.

In a new study, a research team led by Curtin University scientists analyzed biomarkers (molecular fossils) extracted from rocks collected in the United Kingdom’s Bristol Channel and found evidence of ancient microbial mats, which are complex communities of microorganisms.

“Through our analysis of the chemical signature of these microbial mats, in addition to seeing sea-level change and water column freshening, we discovered the end-Triassic mass extinction occurred later than previously thought,” said first author Calum Peter Fox, a Ph.D. student in the Western Australia Organic Isotope Geochemistry Centre at Curtin University and the Department of Earth Sciences at Khalifa University of Science and Technology.

“Previous research suggests the extinction took place where we now know microbial mats flourished and the chemical signatures left by these ancient microbes complicated the rock record, leading others to believe this is where the extinction took place.”

“The microbial mats recorded in UK samples are comparable to extant microbial mats such as in Shark Bay of Western Australia,” he said.

“It’s amazing to consider that similar microbial communities that confounded the timing of one of Earth’s largest extinctions millions of years ago are on our shorelines and so easy to observe for ourselves.”

“The findings not only presented a new theory of what started the end-Triassic extinction, but also provided a type of warning for future potential mass extinction events on Earth,” said senior author Professor Kliti Grice, also from the Western Australia Organic Isotope Geochemistry Centre at Curtin University.

“Our recent research shows that microbial mats played important functions in several mass extinction events as well as a role in preserving remains of life including soft tissue of dead organisms under exceptional circumstances.”

“Knowing more about the carbon dioxide levels present during the end-Triassic mass extinction event provides us with important details that could help protect our environment and health of our ecosystems for future generations.”

The findings were published in the Proceedings of the National Academy of Sciences.

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Calum P. Fox et al. Molecular and isotopic evidence reveals the end-Triassic carbon isotope excursion is not from massive exogenous light carbon. PNAS, published online November 16, 2020; doi: 10.1073/pnas.1917661117

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