Around 252 million years ago, volcanic eruptions set off a geologic domino effect culminating in the largest extinction event in Earth’s history. The end-Permian extinction (EPE), also known as the Permian-Triassic extinction or the Great Dying, wiped out 96% of ocean life and around 70% of terrestrial species.
According to a new study published in the journal Palaios, the eruptions may have led to a spike in wildfires that might have been an EPE driver in eastern Gondwanan forest mires, in what are now Australia and Antarctica. By studying charcoal remains from the EPE, the scientists found evidence that wildfires turned the wetlands into a scorched, sparse landscape.
A Change in Charcoal
Scientists believe volcanic eruptions in the Siberian Traps ultimately caused the end-Permian mass extinction by creating or enhancing extinction drivers like polluted soil and acidic rain. Wildfires have been suggested as drivers too, but no work has analyzed fires before and during the EPE.
To quantify this prehistoric fire activity, Chris Mays, a paleontology lecturer at University College Cork, and coauthor Stephen McLoughlin at the Swedish Museum of Natural History looked at charcoal content preserved in samples from three mid- to late Permian peat deposits in the southern Sydney Basin, the northern Bowen Basin, and eastern Antarctica. Using microscopy techniques to count the remains of burned, charcoalified plants, they found evidence that wildfires were a regular feature of the region before the EPE. “Then, what we discovered is leading up to the mass extinction, there was a great increase in the amount of charcoal being preserved,” said Mays.
A rise in charcoal levels around the EPE suggested that fire activity spiked during the peak of the Siberian Traps eruptions. But looking at rock from the beginning of the Triassic (after the extinction event), researchers were hard pressed to find charcoal, signaling that by that time, wildfire activity may have declined significantly.
Mays said one possible explanation for these results could be that warming from the greenhouse gases released by the Siberian Traps eruptions led to extreme seasonal temperature and precipitation changes. These shifts could have created dry seasons in the wetlands, which, combined with high atmospheric oxygen levels, would have helped wildfires flourish. “Then, after the fact, because [the wildfires] burned off those high-vegetated areas, the fires couldn’t get a good hold in the postextinction realm,” said Mays.
But that hypothesis still needs confirmation. “All we can really say is that on average, the amount of charcoal being produced [during the EPE] was much higher, probably 2 to 3 times higher than preextinction levels,” Mays said. The samples don’t allow researchers to see whether there were seasonal changes in fires from year to year, nor do they show whether the charcoal spike represents an increase in fire frequency or intensity.
David Bond, a professor of paleoenvironments at the University of Hull, said this work represents an important advance in the field. “This is a good study that takes a long-term view, looks at the background conditions,” said Bond. “It’s based on a relatively small number of samples, but that’s the nature of this kind of study.”
Wildfires Then and Now
Today’s wildfire threats are different, and so are the flora and fauna. Although intense fires in fire-adapted areas are common to both the EPE and today, one notable difference between then and now is that modern fires are also tearing through non-fire-adapted areas. “It’s quite difficult to tell how modern ecosystems will react and whether [their response is] going to be similar to what happened back in the day,” said Mays.
Another major difference is the rate of climate change. Today, temperatures and carbon dioxide (CO2) levels are climbing at a faster clip compared to the Permian, on the scale of hundreds of years rather than tens of thousands. But, Mays said, it’s not too late. “We’re still in the early, early stages of that increase in CO2. So we can definitely turn the ship around.”
—Jackie Rocheleau (@JackieRocheleau), Science Writer