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The Triassic-Jurassic extinction event that ended the Triassic period and led to the Jurassic about 200 million years ago was one of the largest mass extinctions in the history of our planet.
In total, around 25-34 percent of marine genera are thought to have been lost during the event and many land groups were wiped out, paving the way for dinosaurs and pterosaurs to dominate Earth for the next 135 million years or so. .
But new research suggests that this extinction event occurred later than initially thought and sheds new light on the contributing factors.
The more widely accepted hypothesis of the Triassic-Jurassic event blames massive volcanic eruptions for the loss of life on the planet, although other ideas have also been advanced – such as asteroid attacks and more gradual climate change.
To get a better idea of what happened, the new study looked at molecular fossil biomarkers from rocks in the Bristol Channel off the coast of England, which at the time was part of the supercontinent Pangea.
The samples showed evidence of ancient microbial mats – complex communities of microorganisms that retain indicators of current weather conditions.
Ecosystem changes in this particular part of the UK and Central European watersheds have long been used as indicators of what happened, with a sudden drop in organic carbon-13 thought to have been an early sign of atmospheric changes that led to this event.
However, it turns out that this was not a direct indicator of the Triassic-Jurassic event, the scientists say, but instead the changes came from changes in sea level and water desalination, which created the perfect conditions for the prosperity of these microbial mats.
These changes put the ocean’s organic composition in a transitional phase, but researchers show that it was tens of thousands of years later, during Late Rhaetian, that the extinction event began in earnest.
“Through our analysis of the chemical signature of these microbial mats, as well as seeing sea level change and water column refreshment, we found that the late Triassic mass extinction occurred later than previously thought, “says Calum geochemist Peter Fox, of Curtin University in Australia.
However, the drop in sea level the team detected may have been a sign of the initial movements in Earth’s tectonics that would lead to these future eruptions and the eventual breakup of Pangea.
This agrees with the results of another study which showed magma activity was occurring in this region 100,000 years before the first known eruption associated with the extinction event.
Looking back through so many millions of years is a difficult and challenging process, but the fossil record that remains on Earth gives us an invaluable record of what the weather was like when these mass extinctions occurred.
Climate change in action, then and now. (Curtin University)
As with most of the work examining the history of life and climate on our planet, the results of this latest study can also be used to inform our understanding of how climate is changing today.
“Our recent research shows that microbial mats played important functions in several mass extinction events, as well as a role in preserving the remnants of life, including the soft tissues of organisms that died under exceptional circumstances,” says geochemist Kliti Grice. of Curtin University.
“Knowing more about the carbon dioxide levels present during the late Triassic mass extinction event provides us with important details that could help protect our environment and the health of our ecosystems for future generations.”
The research was published in PNAS.
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