Ancient sediments reveal Earth’s hidden wildfire past

(Press-News.org) An international team of scientists, including a senior researcher at Heriot-Watt University in Edinburgh, Scotland, has uncovered new evidence of ancient wildfires that reshapes our understanding of Earth’s turbulent Early Triassic epoch, about 250 million years ago.

 

The findings, reported in Communications Earth & Environment, published by Nature Portfolio under the title Wildfire, ecosystem and climate interactions in the Early Triassic, challenge the long-standing belief in a global “charcoal gap”, a time interval with little or no evidence of fire following the world’s greatest mass extinction.

 

Traces in the dirt

 

For decades, the absence of charcoal in the geologic record led scientists to assume that wildfires had all but disappeared after the Permian–Triassic extinction, also known as the "Great Dying”. This was the most severe mass extinction in Earth's history, resulting in the loss of up to 96% of marine species and 70% of terrestrial vertebrate species, primarily caused by massive volcanic eruptions.

 

This latest study sheds new light on this period, revealing microscopic chemical traces of charred vegetation preserved in sediments.

 

The team tested 30 sediment samples retrieved from Svalbard, the Norwegian Arctic archipelago better known today as home to the Global Seed Vault. Despite the harsh conditions, the island’s ancient rocks offered pristine material that had remained undisturbed for hundreds of millions of years.

 

Fire without charcoal

 

Instead of relying on visible pieces of charcoal, the team searched for molecular fingerprints of combustion known as polyaromatic hydrocarbons (PAHs). These compounds form during the incomplete burning of plant matter and can persist in sediments long after more visible evidence disappears.

 

Dr Clayton Magill is Associate Professor of Biogeochemistry at the Lyell Centre at Heriot-Watt University and a senior author of the study.

 

“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,” he said.

 

“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.”

 

The analysis revealed widespread PAHs consistent with burning fresh plant matter rather than volcanic coal deposits or contamination. This strongly suggests that wildfires were, in fact, shaping ecosystems during the Early Triassic, even when the fossil charcoal record seemed to say otherwise.

 

Modelling fire in deep time

 

The project, funded by the Swiss National Science Foundation, combined sediment analysis with cutting-edge climate and vegetation modelling. Using an open-source model by Massachusetts Institute of Technology (MIT) named the General Circulation Model (MITgcm), the team successfully reconstructed how shifting climates, ecosystems, and fire regimes interacted in the aftermath of the mass extinction.

 

“It’s very easy to say, ‘If A occurs, then B will happen,’ but that can be ambiguous,” Dr Magill said. “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 use of open-source models was especially important, Dr Magill added: “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.”

 

The 10-strong team of sedimentologists, palynologists, palaeontologists, physicists and geochemists was led by Dr Franziska Blattmann at the Faculty of Geoscience and Environment at the University of Lausanne in Switzerland. She and her colleagues had worked on the groundbreaking research since 2018 and said: "This study came together through the collaboration of a multidisciplinary team of scientists, working together even amid the challenges of the COVID-19 pandemic. The research highlights how longstanding scientific questions can be advanced and how unexpected discoveries can emerge when collaboration is open, creative and supportive."

 

Beyond filling in a 250-million-year-old puzzle, the research carries urgent lessons for the present. The Early Triassic was a time of extreme climate swings, ecosystem recovery, and environmental stress, all themes with echoes in today’s warming world.

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