An Australian-led team of scientists has shed new light on the timing of one of the most catastrophic mass extinctions in history, which set the stage for dinosaurs to dominate Earth.
Two hundred million years ago, the Triassic period was brought to a devastating end by extensive volcanic eruptions from the Central Atlantic magmatic province (CAMP), which formed as Pangea broke apart. As carbon dioxide spewed into the atmosphere, the Earth’s carbon cycle was disrupted, and the oceans became acidified.
Delicate marine ecosystems collapsed, and a sweep of prehistoric creatures such as conodonts and phytosaurs went extinct – though somehow, plants, dinosaurs, pterosaurs and mammals scraped through. This new world allowed dinosaurs to expand their ecological niche and reign supreme for the next 135 million years.
Evidence for this end-Triassic extinction event comes from two major compositional shifts observed in the carbon isotope record 200 million years ago, as extensive volcanism could have released isotopically light methane into the atmosphere.
Now research led by Curtin University suggests the first shift was actually caused by more localised environmental change throughout European basins, and so the mass extinction may have occurred later on.
Their paper, published in the journal PNAS, describes how the team examined the stable isotope conditions of molecular fossils: traces of organic molecules found in the fossil record. These well-preserved “biomarkers” were extracted from rocks in the Bristol Channel in the UK and indicated the presence of microbial mats, which are complex communities of microorganisms.
Curtin’s Calum Peter Fox, the paper’s first author, explains: “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.”
A drop in sea level in European basins – which may have been indirectly driven by volcanic activity on CAMP – caused localised environmental changes. The marine ecosystem became a brackish, shallow-water environment where microbial mats thrived.
These ancient slimy microbes then produced lighter carbon isotopes, complicating the rock record and causing confusion about the timing and location of the end-Triassic extinction.
According to co-author Kliti Grice, also based at Curtin, the first observed isotope changes therefore don’t coincide with the global extinction event.
“Instead, the mass extinction stage must have happened a bit later, along with the land plant extinctions, toxic levels of hydrogen sulfide and ocean acidification driven by massive volcanic activity linked with the opening of the Proto-Atlantic Ocean,” she says.
It is currently unclear exactly how much later the extinction event occurred. Grice says their new interpretation requires further reanalysis of the carbon isotope record, in order to gain a better understanding of the regional versus global effects of the CAMP.
This research may also reshape our understanding of other mass extinction events – particularly those linked to volcanic activity – and could alert us to future potential mass extinctions on modern Earth.
As fossil fuel consumption drives us further into the climate crisis, Grice explains that “it is important to correlate contemporary conditions and dynamics to past periods of major environmental change and threats. Threats can include decline in biodiversity; ocean acidification; environments with no oxygen; destruction of habitats and degradation; changing nutrient levels and rising and falling sea levels.”
She concludes: “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.”
Lauren Fuge is a science journalist at The Royal Institution of Australia.
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