New clues about Earth's largest mass extinction event

The Late Permian Mass Extinction (LPME) was the largest such in event in the Earth’s history, decimating between 80 and 90 percent of life on our planet. However, the causes of this devastating event and the ways in which it unfolded are not yet fully understood. By analyzing mercury from Siberian volcanoes that ended up in sediments in Australia and South Africa, a team of researchers led by the University of Connecticut (UConn) has managed to shed more light on this mass extinction’s causes and timeline. 

Although scientists have long argued that the rapid warming associated to this event was linked to massive volcanism occurring at a large deposit of lava called the Siberian Traps Large Igneous Province (STLIP), clear evidence for this was still lacking. While volcanoes leave helpful clues in the geological record – such as traces of carbon dioxide and methane launched into the atmosphere and deposited around the globe – it is hard to directly link something like that to the extinction event.

“As geologists, we’re looking for a signature of some kind – a smoking gun – so that we can absolutely point to the cause,” said study co-author Tracy Frank, an expert in Earth Sciences at UConn.

However, the researchers believe that they finally might have found such a “smoking gun” – mercury, one of the heavy metals associated with volcanic eruptions, analyzed from sediments from the Sydney Basin in Eastern Australia and the Karoo Basin in South Africa. 

“It turns out that volcanic emissions of mercury have a very specific isotopic composition of the mercury that accumulated at the extinction horizon. Knowing the age of these deposits, we can more definitively tie the timing of the extinction to this massive eruption in Siberia. What is different about this paper is we looked not only at mercury, but the isotopic composition of the mercury from samples in the high southern latitudes, both for the first time,” explained study lead author Jun Shen, an expert in volcanism at the China University of Geosciences in Wuhan.

“As a starting point, geologists have pinpointed the timing of the major extinction event at 251.9 million years with a high degree of precision from radiogenic isotope dating methods. Researchers know that is when the major extinction event happened in the marine environment and it was just assumed that the terrestrial extinction event happened at the same time,” added co-author Christopher Fielding, a professor of Earth Sciences at UConn.

According to Fielding’s previous research though, the extinction event on land happened about 200,000 to 600,000 years earlier. “That suggests that the event itself wasn’t just one big whammy that happened instantaneously. It wasn’t just one very bad day on Earth, so to speak, it took some time to build and this feeds in well into the new results because it suggests the volcanism was the root cause,” he explained. “That’s just the first impact of the biotic crisis that happened on land, and it happened early. It took time to be transmitted into the oceans. The event 251.9 million years ago was the major tipping point in environmental conditions in the ocean that had deteriorated over some time.” 

“The main point is that we now have a chemical signature in the form of mercury isotope signatures, that definitively ties the extinction horizon in these terrestrial sections that provide a record of what was happening on land due to Siberian Traps volcanism.”

The study is published in the journal Nature Communications.

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By Andrei Ionescu, Earth.com Staff Writer

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