The Triassic-Jurassic extinction, which ended the Triassic period and brought about the Jurassic about 200 million years ago, is one of the largest mass extinctions in the history of our planet.
It is generally estimated that about 25-34 percent of marine species were lost during the event and many land groups were destroyed, clearing the way for dinosaurs and pterosaurs to dominate the Earth for the next 135 million years or so.
But new research suggests that this disappearance occurred later than originally thought, and sheds new light on contributing factors.
The most widely accepted hypothesis of the Triassic-Jurassic event blames huge volcanic eruptions for the loss of life on the planet, although other ideas have been put forward ̵
To get a better idea of what happened, the new study looks at molecular fossil biomarkers from rocks in the Bristol Channel off the coast of England, which was part of the supercontinent of Pangea at the time.
The samples showed evidence of ancient microbial mats – complex communities of microorganisms that retain indicators of weather conditions at the time.
Changes in the ecosystem in this part of the UK and Europe’s central water basins have long been used as an indicator of what has happened, with the sudden decline in organic carbon-13 considered an initial sign of the atmospheric changes that led to the event.
However, it turns out that this is not a direct indicator of the Triassic-Jura event, scientists say – but instead the changes come from changes in sea level and desalination of the water, which creates the ideal conditions for these microbial mats to thrive.
These changes put the organic composition of the ocean in a transitional phase, but researchers show that tens of thousands of years later, during the Late Retian, the extinction event began in earnest.
“Through our analysis of the chemical signature of these microbial mats, in addition to seeing sea level changes and water column refreshments, we found a mass extinction at the end of the Triassic that occurred later than previously thought,” said Calum geochemist Peter Fox. from Curtin University in Australia.
However, the drop in sea level, discovered by the team, may have been a sign of the initial movements in the Earth’s tectonics, which could lead to these future eruptions and the possible collapse of Pangea.
This is in line with the findings of another study, which shows that magmatic activity occurred in this region 100,000 years before the earliest known eruption associated with the extinction event.
Looking back over so many millions of years is a difficult and challenging process, but the fossil recordings that remain on Earth give us an invaluable record of what the weather was like when these mass extinctions occurred.
As with most studies of the history of life and climate on our planet, the findings of this latest study can also be used to inform our understanding of how climate is changing today.
“Our recent study shows that microbial mats have played important roles in several mass extinctions, as well as a role in preserving the remains of life, including soft tissues of dead organisms in exceptional circumstances,” said geochemist Clitty Gris of Curtin University.
“Knowing more about the levels of carbon dioxide present during the mass extinction at the end of the Triassic provides us with important details that could help protect our environment and the health of our ecosystems for future generations.”
The study was published in PNAS.