The world’s oldest evidence of wildfires can be found in a laboratory on the fourth floor of a brick building in Waterville, Maine. To the untrained eye, it looks like black fuzz, not much larger than the head of a pin. To Ian Glasspool, a paleobotanist at Colby College, it’s a piece of charcoal that’s 430 million years old.
The specimen, which Glasspool discovered in a mudstone from south Wales, is one of several pieces of ancient charcoal that have been studied in recent years to investigate how fires burned in the past. Together, these remains help scientists understand how fires have shaped and shaped through environmental changes over geologic time.
“They’re dull-looking things,” Glasspool said, lifting a sample embedded in a small resin disk. “But there’s a lot you can get out of it.”
These age-old insights may not help us manage individual wildfires today, Glasspool said. But they can provide a clearer picture of the global phenomenon of fire and how it affects Earth’s climate. This in turn can help modelers make more accurate projections of future climate.
“The geological record shows it’s a lot more complicated than ‘it’s going to be hot, there will be more fires,’” says Jennifer Galloway, a paleoecologist with the Geological Survey of Canada. Galloway recently published an article in the journal Evolving Earth about the benefits of studying ancient forest fires as a way to understand current climate dynamics.
Fire is a fairly recent phenomenon in Earth’s 4.54 billion year history. For more than 90% of that timeline, the planet’s atmosphere and continents lacked the oxygen and kindling necessary to sustain a flame. Lightning strikes might have charred bits of microbial mat here and there, but the combustion would have been short-lived; smoke and embers were virtually absent. Only after plants appeared on land some 458 million years ago did sustained burns – and eventually a geological record of fire – become possible.
The earliest fires did not burn forests, which were still millions of years away from developing, but simpler vegetation such as mosses and liverworts. “We’re talking about things you can generally walk through without the tops of your boots getting wet,” Glasspool said. A mysterious group of larger growths called nematophytes were also scattered across the landscape at the time, and these could also have helped fuel the earliest flames, he added.
To study the remains of these ancient fires, Glasspool first dissolves his rock samples in acid and then sifts out the tiny black specks that remain. To manipulate and orient each spot for analysis, he uses a wooden skewer with a single whisker from his cat, Bingo, duct taped to the end.
“Low-budget, do-it-yourself,” he said in his lab in February. If he were to use a store-bought brush, his little samples might get caught in the hairs; Bingo’s whisker gives him more control.
Viewed with a simple light microscope, these charcoals reveal marbled cell walls that have been impeccably preserved through carbonization. That process burns off all volatile organic matter, leaving behind only inert carbon, which can remain unchanged for hundreds of millions of years.
Charcoal has a distinct silky sheen that distinguishes it from coal, another form of carbon, which looks dull under a microscope.
By monitoring the amount of charcoal in the rock at different times, Glasspool and his colleagues identified burning patterns that emerged during previous periods of global warming. He and his team discovered a fivefold increase in charcoal in 200-million-year-old sedimentary rocks collected in eastern Greenland. This period marked the end of the Triassic, when intense volcanism raised global temperatures by about 6 degrees Celsius and led to one of the worst mass extinctions in Earth’s history.
In 2010, the Glasspool team reported that rising atmospheric heat could have increased wildfire activity in a number of ways. For example, the heat could have caused thunderstorms with more frequent lightning strikes, the leading natural cause of forest fires, both past and present. According to a study by Imperial College London, just 1 degree Celsius of warming can increase lightning speed by about 40%. This could partly explain why wildfires were so widespread at the end of the Triassic, Glasspool said.
The fossil record also indicates that plants with small, narrow leaves became more common as temperatures rose, while species with broader leaves largely disappeared from the landscape. According to his team, this was most likely a response to the heat, because smaller leaves can escape the heat more easily than larger leaves.
The small-leaved species would have fueled more intense fires, just as torn pieces of paper burn more quickly than intact pieces. “They dried faster and were more flammable,” Glasspool said.
More flammable plants, more smoke and more carbon dioxide in the atmosphere would have further warmed the Earth, perhaps fueling more flames, more changes in vegetation and more intense thunderstorms – a positive feedback loop similar to what appears to be happening today to play.
The rock record gives an idea of how long it may take for ecosystems to recover after such disturbances. Deposits from the late Permian mass extinction – a period of warming some 252 million years ago that marked the greatest loss of human life in all of Earth’s history – suggest that charred wetlands took millions of years to recover after dehydration and burning.
An undated image from IJ Glasspool shows a rock sample with fossilized charcoal as brown and black streaks. | IJ Glasspool via The New York Times
“Let’s hope we don’t recreate that,” says Chris Mays, a paleontologist at University College Cork in Ireland who published studies on these deposits in 2022.
Modern global temperatures have risen much less than they did then: only 1.1 degrees Celsius since 1880, compared with about 10 degrees Celsius during the tens of thousands of years of the end-Permian extinction. But the pace of change today far exceeds that of the past. This rapid warming has made wetlands more susceptible to fire: South America’s Pantanal region, 42 million hectares of tropical wetlands, has begun to burn seasonally at an alarming rate. End-Permian deposits offer a sobering picture of what could happen if climate change continues unabated.
“There are a number of levers we can pull to keep things from getting this bad,” Mays said. “But we use it as an absolute worst-case scenario.”
Sean Parks, a research ecologist with the US Forest Service at the Rocky Mountain Research Station in Missoula, Montana, noted that the size and severity of such fires are also the result of human behavior and land use, not just climate change.
Still, Parks says, studies of the geological record and ancient climate patterns can help improve the global climate models that inform land management decisions: “It’s interesting and excellent background information.”
Fernanda Santos, a staff scientist at Oak Ridge National Laboratory in Tennessee who studies modern fires in Alaska and works closely with climate models, agrees.
“I really appreciate old data because it can give us this new perspective and a new baseline,” Santos said.
This article originally appeared in The New York Times
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