Evidence of the world's oldest wildfire has been discovered in a laboratory on the fourth floor of a brick building in Waterville, Maine. To the untrained eye, it looks like a speck of black lint, not much larger than the tip of a pin. For paleobotanist Ian J. Glasspool of Colby College, it's 430-million-year-old charcoal.
The specimen, discovered by Dr Glasspool in mudstone in south Wales, is one of a number of ancient charcoal fragments being studied in recent years to find out how fires burned in the past. These debris are helping scientists understand how fires formed and were shaped by environmental changes over geological time.
“They look boring,” Dr. Glasspool said, holding up a sample embedded in a small resin disc. “But there’s so much to be gained from it.”
These ancient insights may not be useful in managing individual wildfires today, Dr. Glasspool said. But they can provide a clearer understanding of the global phenomenon of fire and how it shapes Earth's climate. This helps modelers more accurately predict future climate.
“The geological record shows us that the picture is much more complex than 'hotter, more fire',” said Jennifer M. Galloway, a paleoecologist with the Geological Survey of Canada. Dr. Galloway recently published a paper in the journal Evolving Earth. On the benefits of studying ancient wildfires as a way to understand today's climate change.
Fires are a very recent phenomenon in Earth's 4.54 billion year history. For more than 90% of that timeline, Earth's atmosphere and continents lacked the oxygen and spark needed to sustain the flames. The lightning strike may have scorched parts of the microbial mat, but the combustion would have been short-lived. There was almost no smoke or embers. It wasn't until the appearance of plants on land, about 458 million years ago, that sustained, and eventually geological, fire records became possible.
Early fires burned simple plants such as moss and liverwort, rather than forests that were still millions of years old. “What we're talking about is something you can generally walk through and not even get the top of your boot wet,” Dr. Glasspool said. A mysterious group of large growths called nematodes also dotted the landscape during this time, and these may have also helped fuel early fires, he added.
To study the remains of these ancient fires, Dr. Glasspool first dissolves rock samples in acid, then sifts out the tiny black specks left behind. To manipulate and orient each spot for analysis, he uses one of his cat Bingo's whiskers, a wooden skewer duct-taped to the end.
“It's low budget and I'll do it myself,” he said from his lab in February. If you use a commercially available paintbrush, small samples can get caught in the bristles. Bingo's beard gives him even more control.
Examining these charcoals under a simple light microscope reveals marble-like cell walls that are naturally preserved through the act of carbonization. In this process, all volatile organic matter is burned away, leaving only inert carbon, which may remain unchanged for hundreds of millions of years.
Charcoal has a distinctive silky sheen that helps distinguish it from coal, another form of carbon that looks more matte under a microscope.
By tracking charcoal abundance at different intervals in the rock record, Dr. Glasspool and his colleagues identified fire patterns that emerged during periods of past global warming. He and his team found that charcoal in the 200 million-year-old sedimentary rocks he collected in East Greenland had increased fivefold. This period marked the end of the Triassic period, when intense volcanic activity raised global temperatures by about 6 degrees Celsius and triggered one of the worst mass extinctions in Earth's history.
In 2010, Glasspool's team reported that increased atmospheric heat may have increased wildfire activity in a number of ways. For example, warmer weather may have caused thunderstorms and more frequent lightning strikes. This was and still is the main natural cause of wildfires. According to research from Imperial College London, just a 1 degree rise in temperature can increase the incidence of lightning by around 40%. This may partly explain why wildfires were so widespread at the end of the Triassic, Dr Glasspool said.
The fossil record also shows that as temperatures rose, plants with small, narrow leaves became more common, while species with wider leaves all but disappeared from the landscape. His team reported that this was most likely a response to warmth, as small leaves can dissipate heat more easily than larger leaves.
Seeds with smaller leaves may have caused more intense fires, just as torn pieces of paper burn faster than intact paper. “They dried faster and were more flammable,” Dr. Glasspool said.
More flammable plants, smoke, and carbon dioxide in the atmosphere would have warmed the planet even more, possibly resulting in more flames, more vegetation changes, and more intense thunderstorms. Positive feedback loops are no different than what seems to be happening today.
The rock record can tell us how long it takes for an ecosystem to recover after such a disruption. Sediments from the end-Permian mass extinction (a period of warming approximately 252 million years ago that recorded the greatest loss of life in Earth's history) were left behind until the charred wetlands dried and flared, then recovered. This suggests that it took several million years.
“I hope it never happens again,” said Chris Mayes, a paleontologist at University College Cork in Ireland who published a study on these deposits in 2022.
Global temperatures today are much lower than they were then, rising only 1.1 degrees Celsius since 1880, compared to about 10 degrees Celsius in the tens of thousands of years after the end-Permian extinction. However, the rate of change today is much faster than in the past. This fast-paced warming already makes wetlands more prone to fires. The Pantanal region of South America, a 42 million acre tropical wetland region, is beginning to experience seasonal fires at an alarming rate. Late Permian deposits offer a sobering look at what will happen if climate change continues unabated.
“There are a lot of levers we can pull to prevent it from getting that bad,” Dr. Mays says. “But we're using that as the absolute worst-case scenario.”
Sean Parks, a research ecologist with the U.S. Forest Service at Rocky Mountain Research Station in Missoula, Montana, said the extent and severity of these fires is a result of not only climate change but also human behavior and land-use practices. He also pointed out that.
Still, Dr. Parks said that studying the geological record and ancient climate patterns could help improve global climate models that inform land management decisions. This is background information.”
Fernanda Santos, a staff scientist at Tennessee's Oak Ridge National Laboratory who studies modern fires in Alaska and works closely with climate modelers, agrees.
“I really value ancient data because they give us new perspectives and new baselines,” said Dr. Santos.
