Wildfires raged on after Earth's worst mass extinction

Fire once seemed strangely absent from Earth’s history right after the worst mass extinction the planet had ever seen.

This stretch of time, about 250 million years ago in the Early Triassic, looked like a world with hardly any wildfires. The rocks showed almost no charcoal, and that lack of evidence grew into a story about a planet without flames.

New work now suggests that story missed something important. Fires were still burning. They just left a different kind of trace – one that hides in chemistry instead of the obvious black bits of charcoal people usually expect to find.

The study was led by Dr. Franziska Blattmann, an expert in the Faculty of Geoscience and Environment at the University of Lausanne.

The story of the Great Dying

The mass extinction at the end of the Permian period, often called the “Great Dying,” wiped out up to 96% of marine species and 70% of terrestrial vertebrate species.

Scientists tie this disaster mainly to huge volcanic eruptions that pumped heat-trapping gases into the air, pushed temperatures up, and stressed ecosystems on land and in the oceans.

An international research team has now shown that wildfires did not vanish in the Early Triassic aftermath. The study points to fire as an active part of those recovering landscapes.

Rethinking a missing charcoal story

For decades, the idea of a global “charcoal gap” shaped how people thought about this time.

Geologists went through rock layers from the Early Triassic and found very little visible charcoal. The resulting view was that the planet’s vegetation was so damaged and the air so low in oxygen that fires could barely start or spread.

That picture now looks incomplete. Instead of searching only for visible charcoal or burnt wood, the team turned to compounds that can persist even when all the obvious black fragments have broken down.

The results show that fire was present and interacting with early Triassic ecosystems even when the rock record looked deceptively quiet.

Finding fire in the smallest traces

Study senior author Dr. Clayton Magill is an associate professor of biogeochemistry in the Lyell Centre at Heriot-Watt University.

“A lot of folks have not found the normal evidence of fire such as charcoal, ash, burnt fossils so the consensus was that fire wasn’t happening,” said Dr. Magill.

“What our colleague Dr. Franziska Blattmann’s work showed is that even without the big pieces of evidence, the microscopic signals are still there. You just need to know where to look.”

Those signals are tiny bits of organic chemistry buried in ancient mud and now turned to rock.

Arctic rocks and chemical fingerprints

The researchers studied 30 sediment samples taken from Svalbard, a Norwegian Arctic archipelago that’s also home to the Global Seed Vault.

The rocks there hold layers that have stayed mostly untouched for hundreds of millions of years, which makes them strong records of ancient environments.

Instead of searching for visible charcoal, the team measured polyaromatic hydrocarbons, or PAHs. These molecules form when plant material burns but doesn’t completely burn up. They can remain locked in sediments long after ash and charcoal are gone.

The specific pattern of PAHs they found matched the burning of fresh plant matter, not coal from volcanic activity or modern contamination, which points strongly to wildfires actively burning in those Early Triassic landscapes.

Traces of fire in the Early Triassic

The project, funded by the Swiss National Science Foundation, did not stop at chemical measurements.

The team combined their sediment results with climate and vegetation modeling, using an open-source tool developed at the Massachusetts Institute of Technology called the General Circulation Model (MITgcm).

This allowed them to explore how climate, plant cover, and fire behavior interacted after the mass extinction.

“It’s very easy to say, ‘If A occurs, then B will happen,’ but that can be ambiguous,” noted Dr. Magill. “By using models, we can run our data through theory and test whether it holds up. It doesn’t just say, ‘trust me’ – it shows you the evidence.”

The simulations revealed which conditions matched the chemical signals in the rocks and which did not.

Open science and shared tools

The modeling was built on open-source software, which means other scientists can access the code and use it freely.

“That’s a powerful tool in a world where not everyone has equal access to scientific resources and funding. Open science allows everyone to compete at the highest level,” said Dr. Magill.

That approach makes it easier for groups in different countries and with different funding levels to repeat, check, or extend the work.

The open-source software also helps link studies of ancient climate to the tools used for modern climate research, because many of the same physical principles apply whether the year is 2025 or 252 million years ago.

Working through a global crisis

The research team included ten specialists in sedimentology, palynology, paleontology, physics, and geochemistry – each contributing a different skill to understand fire, climate, and ecosystems in the Early Triassic.

The experts began the project in 2018 and kept it moving through a tough stretch for research around the world.

“This study came together through the collaboration of a multidisciplinary team of scientists, working together even amid the challenges of the COVID-19 pandemic,” said Dr. Blattmann.

“The research highlights how longstanding scientific questions can be advanced and how unexpected discoveries can emerge when collaboration is open, creative and supportive.”

The full study was published in the journal Communications Earth & Environment.

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