According to new research led by the University of Oxford, episodic volcanic activity is likely to have played a key role in triggering the end-Triassic mass extinction (201.5 million years ago), which set the scene for the rise and age of the dinosaurs.
The Mount Bromo volcano on the island Java of Indonesia. Image credit: Jan-Pieter Nap / CC BY-SA 3.0.
The end of the Triassic period witnessed one of the largest mass extinctions of animal life known from Earth history.
The casualty list includes large crocodile-like reptiles and several marine invertebrates. The event also caused changes in land vegetation, and while it remains a mystery why the dinosaurs survived this event, they went on to fill the vacancies left by the now extinct wildlife species, alongside early mammals and amphibians.
This mass extinction has long been linked to a large and abrupt release of carbon dioxide into the atmosphere, but the exact source of this emission has been unknown.
Following the discovery of volcanic rocks of the same age as the extinction, volcanic carbon dioxide emissions had previously been suggested as an important contributor to this extinction event.
Previous studies have also shown that this volcanism might have occurred in pulses, but the global extent and potential impact of these volcanic episodes has remained unknown.
These volcanic rocks covered a huge area, across four continents, representing the Central Atlantic Magmatic Province (CAMP).
University of Oxford researcher Lawrence Percival and colleagues set out to trace the global impact of major volcanic gas emissions and their link to the end of the Triassic period.
The findings link volcanism to the previously observed repeated large emissions of carbon dioxide that had a profound impact on the global climate, causing the mass extinction at the end of the Triassic Period, as well as slowing the recovery of animal life afterwards.
By investigating the mercury content of sedimentary rocks deposited during the extinction, the team revealed clear links in the timing of CAMP volcanism and the end-Triassic extinction.
Volcanoes give off mercury gas emissions, which spread globally through the atmosphere, before being deposited in sediments.
Any sediments left during a large volcanic event would therefore be expected to have unusually high mercury content.
The scientists sourced six sediment deposits were sourced from the UK, Austria, Argentina, Greenland, Canada and Morocco, and their mercury levels analyzed.
Five of the six records showed a large increase in mercury content beginning at the end-Triassic extinction horizon, with other peaks observed between the extinction horizon and the Triassic-Jurassic boundary, which occurred approximately 200,000 years later.
Elevated mercury emissions also coincided with previously established increases in atmospheric carbon dioxide concentrations, indicating release of this gas from volcanic degassing.
“These results strongly support repeated episodes of volcanic activity at the end of the Triassic, with the onset of volcanism during the end-Triassic extinction,” Percival said.
“This research greatly strengthens the link between the Triassic mass extinction and volcanic emissions of carbon dioxide.”
“This further evidence of episodic emissions of volcanic carbon dioxide as the likely driver of the extinction enhances our understanding of this event, and potentially of other climate change episodes in Earth’s history.”
The research is published in the Proceedings of the National Academy of Sciences.
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Lawrence M. E. Percival et al. Mercury evidence for pulsed volcanism during the end-Triassic mass extinction. PNAS, published online June 19, 2017; doi: 10.1073/pnas.1705378114
