A “Botanical Pompeii” Beneath Our Feet Three hundred million years ago, Illinois was tropical rain forest; its climate change holds the key to ours.

Mary Parrish painted this reconstruction of a different Carboniferous-era forest for the Smithsonian. Because it grew later than the Riola forest, the landscape is a bit different, with the tree ferns dominant.

In 2005, two geologists went deep underground to inspect a mine in eastern Illinois. What they found was a perfectly preserved rainforest 300 million years old.

Scott Elrick and John Nelson were checking out the Riola coal mine, just southwest of Danville, for the Illinois State Geological Survey. They were not expecting to discover a lost world, just to note a few geologic features and go home to dinner. They descended half a mile into the mine’s humid black depths … then looked up.

The flat gray shale of the mine’s ceiling was patterned with black leaf and branch shapes—distinct but abstract, like a contemporary textile print. Fossils of long-ago plants that had fallen on a forest floor.

They were not expecting to discover a lost world, just to note a few geologic features and go home to dinner. They descended half a mile into the mine’s humid black depths … then looked up. 

Any fossil is a bit of a miracle: Fewer than one percent of all species wind up so elegantly preserved. All the variables must align before something as fragile as life can be immortalized. Still, this was a likely place for it to happen: This coal had been formed in the Pennsylvanian period, cooked from the compressed peat on the floor of lush, swampy rain forests. Some of that foliage was bound to be preserved.

There was something beyond extraordinary about these fossils, though. As more coal was mined and more “ceiling’ was uncovered, the geologists began to see huge tree trunks, upright stumps, intact seed bundles.

The leafy branches of a calamite tree. Note how the leaves themselves (which are thin and elongate) are arranged in whorls on the stems. © 2005 University of Illinois Board of Trustees. Used by permission of the Illinois State Geological Survey. Photo by Scott Elrick.

They were staring at the bottom of a vast, perfectly preserved forest that somehow, by some wild natural coincidence, had been fossilized all at once, 300 million years ago. And nearly every species that had flourished there had gone extinct.

 

•  •  •

 

Nelson hurriedly called in two experts—Bill DiMichele, a paleontologist at the Smithsonian’s National Museum of Natural History, and Howard Falcon-Lang, a geologist at the University of Bristol in the U.K.—and they all walked through the ancient forest together.

And walked. And walked. The largest similar find had been 400 square yards. This one stretched 4 square miles—ten times the previous area, with exponentially more information trapped in the rock. Wearing miner’s headlamps, their spotlights crisscrossing as they gazed up, the scientists moved through a cathedral-like landscape that reminded Elrick of The Lord of the Rings.

No other setting could duplicate the feeling, thought DiMichele. “We are in the peat body.” The darkness was absolute; if their lights were to fail, their eyes would never adjust to it. The stillness was absolute, too: Everywhere they looked, stories of that lost world were frozen in the rock. He felt at once elated and humbled: Few people would ever experience this.

Newspapers and magazines reported the find with bold headlines. Discover Magazine named it one of the top science stories of 2007. The larger significance began to dawn on the scientific community: An article soon appeared in Science titled “Forests of the past; a window to future changes.” DiMichele told The New York Times the site was “a botanical Pompeii, buried in a geological instant.”

Before they could extract prophetic clues from the forest, the team had to figure out how that happened.

 

•  •  •

 

If you start in St. Louis—in the heart of the heart of the country, as William Gass put it—and head south, you will be driving backward through geologic time. “The rocks are getting older by about 18 million years per mile,” explains Dr. Bruce Stinchcomb, professor emeritus of paleontology at St. Louis Community College-Florissant Valley. “In Madison or Iron County, some of the rocks are two billion years old, and there are chunks of rock embedded in granite that might be even older. Younger sediments have weathered away, eroded. But Illinois is different: It is a basin, and it has accumulated sediments.”

Sediments that are full of fossils. Fossils that take us back to a world we could never otherwise fathom.

I live in Illinois, and I had no idea. Granted, I have made a shameful habit of ignoring prehistory. Those little hard plastic gray or green dinosaurs held zero appeal when I was a kid, and I sat out the Jurassic Park craze with no sense of deprivation.

Now, though, this strange, frozen forest has taken hold of my imagination.

I am so very tired of worrying about the world. Waking to less birdsong; watching temperatures swing wildly and storms turn violent and infections rage; listening to nightly news reports that swing between fire and draught… For just a minute, I need a way to think about the planet without a lurch of fear; a way to be fascinated again, without grief.

Most of the natural world we know today bears only a tenuous relationship to that lost world—yet we are its heirs. “Before I was born out of my mother generations guided me,” Walt Whitman wrote, seeing, as only he would have dared, the coalescence of the planet and the layering of geological strata as precursors to his own idiosyncratic life.

So I pore over Elrick’s fossil photos, the fern fronds and blade leaves and scaly trees, like they are snapshots in a family album. Dinosaurs are not yet born. There are no flowers, because pollinators do not yet exist. Flat, corn-rowed Illinois, which set a record winter low of thirty-eight degrees below zero last January, is tropical, sunning itself close to the equator.

Most of the natural world we know today bears only a tenuous relationship to that lost world—yet we are its heirs. “Before I was born out of my mother generations guided me,” Walt Whitman wrote, seeing, as only he would have dared, the coalescence of the planet and the layering of geological strata as precursors to his own idiosyncratic life.

Elrick and Nelson, men who could read millions of years’ history in a rock, understood that lineage too.

Their improvised team of paleontologists began the largest-ever study of its kind. For the first time, it would be possible to understand an ancient forest as a whole, figuring out how various species grew there and how the ecosystem organized itself. They would be taking the measure of this vast space at a single point in time. And they would have a “worm’s eye view,” with all manner of clues littering the floor of this primeval forest.

Even that long ago, the team realized, trees of the same kind clumped together in copses, just as they do now. In every era, it seemed, a forest was organized according to an inherent logic, one that endured over time. “It was very, very similar in how it was set up,” Elrick says, his scientific demeanor melting into a kid’s exuberance. “That implies there’s some kind of rule set on how ecosystems behave, and that’s pretty cool.”

A small branch from the crown of what appears to have been a tall tree with a highly branched crown. The tiny diamond patterns seen on the stem are called “leaf cushions”, the place at which leaves were attached to the stem when the plant was alive. © 2005 University of Illinois Board of Trustees. Used by permission of the Illinois State Geological Survey. Photo by Scott Elrick.

But what ended this particular forest so suddenly? It had to be something that would let the mud flow in slowly and gently, preserving the tiniest of plants as it hardened. Now a gray shale, it held a confusion of tree fern leaves and stems, like necklaces carelessly tossed together in a drawer, but with delicate details intact. Caught in rock, the Neuropteris ovata seed fern had fronds with exquisite rounded leaves, the sort a florist would reach for to cushion a single red rose.

These plants had not traveled far to be buried, the team knew. No overwhelming, cataclysmic force had swept them miles from home. Yet tree stumps had been preserved upright, which suggested a very rapid deposit of quite a lot of sediment.

Something gentle but momentous, gradual but sudden? Wondering if somehow the earth had shifted beneath the forest floor, the geologists went looking for a fault line. The Royal Center fault had already been mapped in north-central Indiana, its line traced to a spot just northeast of the mines. Sure enough, the team found a long clay dike in the coal, a mud-filled crack that lined up neatly with the Royal Center fault.

Just by looking at that chalky shale, they could tell when a spring tide had come, either at a new moon or a full moon, and when a neap tide had followed, seven days later. The rock held a clear record of seasonal high tides and even daily tides.

This fracture, they deduced, had caused one part of the forest to slowly sink. Then—abruptly, judging from the geological signs—the same fault had triggered an earthquake. That rough jostling dropped part of the mire right below sea level. Water rushed in, drowning the forest—which was in a low-lying estuary, with a river the size of the Mississippi running alongside it—then receded. Over the next three or four months, the tide ebbed and flowed, washing over the forest. Each time, it left behind a layer of sediment called a tidal rhythmite.

Nelson and Elrick measured the thickness of those tidal rhythmites, now stacked as layers of sediment in the shale. (The miners had called it “stack rock” without knowing what they were seeing.) There were distinct, repeating stripes, like the rings of a tree, and the geologists could see the classic thick-thin pattern of sediment that is dropped by a tide going in and out of a narrow opening. Just by looking at that chalky shale, they could tell when a spring tide had come, either at a new moon or a full moon, and when a neap tide had followed, seven days later. The rock held a clear record of seasonal high tides and even daily tides.

“You can actually put your finger on the rock and say, ‘That’s a month. That’s two months,’” Elrick explains. “You can say a tree trunk on the mine’s roof was buried in a matter of three months. So when you’re talking about 300 million years ago, this event took place over a few months, which is, in geologic time, effectively instantaneous.”

By measuring with meticulous precision, they had reached a timeline, a pattern, and a narrative that made sense: Ushered in by the earthquake, the sea dropped a fifteen-foot blanket of sand, mud, and sediment in just a few months. The forest was smothered by the muck.

 

•  •  •

 

I pepper Elrick with questions, and after he generously deluges me with information, I sneak away to other sources, desperate for some basic context.

The forest fossilized in the Carboniferous period, which came after the Devonian—when the forests spread and fish began to walk on land—and before the Permian, when much of the planet’s surface turned to desert. Continents we now know as separate land masses were still stuck together in a single supercontinent, Pangaea, surrounded by a global superocean called Panthalassa. I test the names on my tongue, say them aloud in nonsensical sentences. It feels strange to me, unmoored, to think of North America breaking off and drifting north much later.

Still not sure how we chart the earth’s past, I call Stinchcomb, who has the relaxed, amiable way of a natural storyteller. We talk about what ended each period of flourishing. Glacial and interglacial fluctuation, ice ages and greenhouses, wet air and dry air—the causes are too variable and complicated for me to keep straight. Should we even worry about climate crisis, when it seems to be such a natural part of Earth’s history?

“Ah, but these are big chunks of time,” he says, his tone light at first but grim by the end of the sentence. “A lot of extinction has gone on in the last five hundred years, and it is accelerating. Five hundred years? Geologic time goes in billions of years. This is unprecedented.”

Worn into patience by decades of teaching, he walks me through prior extinctions.

We obsess over dinosaurs, but with a hint of smug pity: Clearly, they were insufficiently evolved, unable to adapt to change.

At the end of the Ordovician period, more than 400 million years ago, a short but intense ice age lowered the sea level. This exposed silicate rock that pulled carbon dioxide out of the atmosphere, cooling the planet and extinguishing eighty-six percent of all species.

At the end of the Devonian period, a lot weirdly bony, spiky, heavily armored fish went extinct; they would look nightmarish to us now.

In the first half of the Carboniferous Period, called the Mississippian, seas covered much of what is now North America. (This is why we have so much limestone, and why you can find coral fossils in Midwestern rock.)

In the second half, the Pennsylvanian, the sea receded, allowing tropical rain forests to grow…until their habitat changed. Elrick had mentioned that eighty-seven percent of peatland tree species went extinct.

After the Carboniferous, the air dried, and much of the Earth’s land turned to desert for the fifty million years of the Permian period. Its end, 251 million years ago, is called “the great dying”: a perfect storm of natural disasters that raised global temperatures and acidified the oceans, killing off ninety-six percent of species.

Then came the Mesozoic Era (“the only one Americans know, because of Jurassic Park,” grumbles Stinchcomb). The dinosaurs roamed for roughly 165 million years, only to become extinct at the end of the Cretaceous period, when photosynthesis halted and the food chain crumbled. We obsess over dinosaurs, but with a hint of smug pity: Clearly, they were insufficiently evolved, unable to adapt to change. But what stopped photosynthesis?

“What we think of as nuclear winter,” says Stinchcomb, “caused by dust in the stratosphere that remained there for centuries. The asteroid that hit the Yucatán peninsula is one explanation for the final coup de grace; I tend to agree. In any event, there was massive catastrophe worldwide.”

The scale makes me shudder. And yet, there is comfort in these huge sweeps of time, and in the irrepressible life force that kept returning in new and fantastic shapes. Again and again, some new plant or creature slips into a niche in the ecosystem and make this planet its home. It awes me, this resilience.

Except, of course, these species are all gone.

 

•  •  •

 

What if we could time-travel back to that supercontinent, parachute into the rainforest just before it drowns in sediment? Instead of the dark misty tangle of today’s Amazon, we see collections of tall poles, some reaching up 120 feet, with sunlight streaming between them. These six-feet-around lycopsids are covered in such distinct scales that miners will later mistake their fossils for dinosaur remains.

The trees also have grass-like leaves, with blades as long as three feet but no branches until you reach the crown, which is just a little topknot for reproductive purposes. These topknots form late in life, as launching pads for spores, but they do not create the dense, light-blocking canopy of the modern rainforest. Instead, the dominant visual is the sunlit poles, which stand arrow-straight, even though they have only a small cylinder of wood in the center of their trunk. Their ring of bark, often a foot thick, supports them.

These are typical leaves from the giant lycopsid trees. Such leaves are grasslike, but could exceed three feet in length. They covered densely the trunk and crown branches of the trees. © 2005 University of Illinois Board of Trustees. Used by permission of the Illinois State Geological Survey. Photo by Scott Elrick.

Far below the tops of the lycopsid poles grows a sub-canopy of rare, mossy green tree ferns, related not to today’s tree ferns but to Marattiales. (One of the most primitive ferns left on Earth, Marattiales are still tropical but no longer anywhere near tree-sized.) In the Carboniferous period, tree ferns could reach thirty feet in height, with feather-duster crowns of long, soft fronds. Beneath them is a froth of seed ferns, which are not ferns at all, but seed-bearing plants with leaves that look like fronds. Some stand as short trees; others collapse together in thickets.

There are also cordaites (like our conifer evergreens but ranging from shrub height to a small tree) and calamites, or “giant horsetails,” easily as tall as trees. I smile at the familiar word: I know horsetail. A scouring rush, its stems are so rough they were a pioneer Brillo pad, used to scrub pots and later to shape oboes. Also called puzzlegrass or snake grass, it is an intense green and wears black bands around its jointed, bamboo-like nodes. (The pattern of spacing between those nodes inspired Scottish mathematician John Napier to invent the logarithm, which I am told shows up in music, math, fractals, statistics, and computer science.) But today’s horsetail is nowhere near the height of these.

Shakespeare could have set A Midsummer Night’s Dream in this forest. The enchantment is the steamy humidity, which allows lush foliage that soaked the air with oxygen—thirty-five percent, compared to the thin twenty-one percent we breathe today. The insects (who have no predators, because birds do not yet exist) grow into giants. The Carboniferous iteration of a dragonfly, Meganeura, has a wingspan of thirty inches.

The connection eludes me. Why would moist, oxygenated air create giant bugs?

“If you’re an insect, there’s only so much air you can force through the rigid spirochetes in your abdomen,” Elrick explains. “So if you have more oxygen, you grow bigger.”

In my dreamy state, his words seem to carry a moral. We are no good at playing to a living thing’s weakness. Oxygen-limited creatures need to be in an oxygen-rich atmosphere to flourish and grow big—that makes perfect sense. By analogy, then, humans with cognitive limits should be placed in an extra-rich educational environment, and those with a limited capacity for love should be immersed in love. Yet we often wind up doing just the opposite.

Shakespeare could have set A Midsummer Night’s Dream in this forest. The enchantment is the steamy humidity, which allows lush foliage that soaked the air with oxygen—thirty-five percent, compared to the thin twenty-one percent we breathe today.

The same logic holds for fragile ecosystems and endangered species, and we are not focusing hard on their limits, either. But that is the worry I am trying to escape. I refocus on those giant dragonflies. They are often called griffinflies, in homage to their mythical size and predatory powers. They flit and soar through the forest, hunting prey with gigantic eyes, their iridescent, sculpted bodies hinging the doubled pair of fine-meshed, transparent wings.

The largest insect ever, griffinflies will leave no fossils in our drowned forest, and the Carboniferous period’s beta-version cockroaches, which made a tasty snack for the griffinflies, will leave only a wing or two. When the ground begins to sink, only what is rooted in place is trapped. Any creature that is mobile will have time to flee—even the arthropleura, invertebrates that look like millipedes but, thanks to that abundant oxygen and zero predation, grow to an eye-popping eight feet long.

Topple the tallest person you know, and the arthropleura will be longer. “They were quite a beast,” Elrick says, chuckling. “We have a lot of their footprints, fewer of the body fossils, ’cause these guys tended to fall apart.” Constructed of about thirty jointed, plated segments, they glided across the forest floor, swerving to avoid trees and rocks. I picture a Chinese parade dragon, its segments bending and twisting. Less ferocious than dragons, they had small, soft mouths, Elrick adds, “so really, they’re herbivores. Millipede cows.”

The day I caught my first glimpse of an indigo bunting, a flash of electric blue arcing from one treetop to the next, I raced home to dig out a bird book and name that tiny jolt of beauty. Now I read that if southern Illinois’s climate warms by just three more degrees, the indigo bunting will lose a third of its habitat.

How cool, that all this lush weirdness ever even existed, I think happily. Too bad that I missed shinnying up a lycopsid or petting an arthropleura, but this speculative loss does not stab my heart the way today’s endangered species do.

The day I caught my first glimpse of an indigo bunting, a flash of electric blue arcing from one treetop to the next, I raced home to dig out a bird book and name that tiny jolt of beauty. Now I read that if southern Illinois’s climate warms by just three more degrees, the indigo bunting will lose a third of its habitat. The shy, elusive little Abbott’s duiker, a forest antelope I would love to photograph, is nearly extinct. So are mountain gorillas, the sultry Amur leopard, the Sumatran elephant, leatherback sea turtles, and at least a fourth of the world’s plant species, including the St. Helena olive tree and the Western Prairie fringed orchid. The list goes on, like a litany of lost saints.

I would far rather shut my eyes and envision the exotic creatures of a pre-prehistoric world.

 

•  •  •

 

“The fossil forest records the death of the peat swamp,” Elrick says. “It’s the last gasp.” And he and his colleagues were the last scientists to behold it. All that they saw in the roof of the mine is now gone: It fell to the ground and fell apart. “These layers have clay in them,” he explains, “and when it gets wet, it expands, and when it gets dry, it shrinks.” Soon after it was exposed, the shale shattered.

At least the team had moved swiftly, extracting plenty of samples for the Smithsonian and a big fossil-covered slab of shale for the Museum of Science and Industry in Chicago.

The mine shut down in 2006.

Today, the closest living relative of the 100-foot lycopsids is quillwort, a spiky, weedy little marsh plant about six inches tall.

Elrick was over the moon to find a whole forest and learn how little had changed in forest ecology, even when the landscape was entirely different. I ask him what, a dozen years later, he sees as the ultimate significance of this find. I am expecting to hear more about the intricate balance of relationships in a primeval forest.

“The interplay of plants with climate and extinctions, and what that can tell us about today’s crisis,” he startles me by saying instead.

And with a thud, I land right back in the despair I was trying to avoid.

“The Earth was experiencing a greenhouse episode then, too,” Elrick reminds me. “There was a short period of temperature rise, averages shooting up by as much as six degrees Celsius.”

He pulls back and makes one last valiant attempt to convey the big picture: “There’s a kind of heartbeat rhythm. Every 100,000 to 120,000 years, as a result of how the Earth goes around the sun, we cycle from circular orbits to elliptical orbits. When the orbit is very elliptical, the Earth is farther from the sun, so the climate cools and you have a glacial cycle. When the orbit is circular, the climate warms, and you have an interglacial cycle. When you look who lived in the peat forests as they were forming and who was there at the very end, they are different, and that’s because of the change in climate as it goes from a glacial to an interglacial cycle, heating up, the ice melting—which is why the tides were coming across the forest.”

What was ominous was the speed of fluctuation: global warming, global cooling, global warming. The cycle was fluctuating too fast, and the rapid shifts kept forcing the forest areas to contract. The dramatic changes in climate and sea level overstressed the plant life. Meanwhile, the humidity that had let the rain forests grow bright and lush was drying out. The forests that had covered the Earth for fifteen million years could not withstand the shift. Deprived of habitat and food, all those interesting animals died out, too.

In other words, the earthquake that drowned our four-mile forest only hastened the local consequences of a much larger shift, as an increase in carbon dioxide made the climate dryer across the supercontinent.

What was ominous was the speed of fluctuation: global warming, global cooling, global warming. The cycle was fluctuating too fast, and the rapid shifts kept forcing the forest areas to contract.

“The dominant plants were lycopods,” Elrick says, “and they went extinct in this period. What we have been able to tease out is that they died because of a climate change, with a rise in carbon dioxide that made the climate much dryer. And that has interesting analogs for today.”

“Forests of the past; a window to future changes.” I went back to that article in Science. The authors wrote that “the study of past forest change provides a necessary historical context for evaluating the outcome of human-induced climate change… Species extinctions appear to have occurred primarily during periods of high climatic variability.”

I had gotten so caught up thinking of trees like giant asparagus stalks and millipedes the size of cows that I had forgotten: What wiped them out was the same sort of climate crisis I was trying not to think about.

Except that ours is far swifter and more extreme.

 

•  •  •

 

We have entered the sixth extinction. Ice is melting, sea levels are rising again (and could come up more than six feet before the end of the century), rainforest is vanishing, and coastlines are eroding.

Half of all species will be extinct by 2100, predicts the venerable biologist Edward O. Wilson. Before human beings spread across the Earth, “the average rate of species extinction was one species per million in each one- to 10-million-year interval,” he wrote in The New York Times last year. “Human activity has driven up the average global rate of extinction to 100 to 1,000 times that baseline rate.” That wide and imprecise range hands ammo to the skeptics. But as hard as the rate is to pin down—because there are so many species on Earth we have yet to name—the number is definitely accelerating.

We are in the Anthropocene period.

Humans tend to name things for their usefulness to humans. We named the Carboniferous period for all that coal formation that had come in so handy. Now, we are living in a period that bears our own name, because it is not ice or forest but humans who are the catalysts for extinction.

The Center for Biological Diversity estimates that “99 percent of currently threatened species are at risk from human activities, primarily those driving habitat loss, introduction of exotic species, and global warming.”

The company whose excavation made it possible to discover the fossil forest, Peabody Energy, is the world’s leading supplier of coal—the burning of which is now accelerating the next extinction.

Pressed into bankruptcy in 2016, Peabody emerged with $2 billion in debt, but by 2018, its revenue was $5.58 billion; it sold 187 million tons of coal that year.

Until I brushed up against those 300-million-year-old ferns, I thought of coal and pollution and global warming as a single, dense lump of worry, uncomplicated by history or irony. Now, when I read that eighty-two percent of the mix of greenhouse gases causing our warming is carbon dioxide released by burning fossil fuels, my mouth twists wry. Because a good chunk of what we are burning is coal created 300 million years ago in a world that then collapsed.

People tell you to be optimistic—human ingenuity and all that. Instead, I gave away my last scrap of mental peace by reading The Uninhabitable Earth, in which David Wallace-Wells reports that more than half of the carbon exhaled into our atmosphere by burning fossil fuels was emitted in the past three decades—after widespread public alarms had been raised.

Those little plastic dinosaurs? A future civilization might craft something similar in the image of Homo sapiens.

By 2050, the United Nations predicts, there will be 200 million “climate refugees.” Because they will be forced to seek safety in countries that do not want them, politics will turn even more chaotic. We are all scrabbling for a foothold on what nature writer Barry Lopez calls “the throttled Earth—the scalped, the mined, the industrially farmed, the drilled, polluted, and suctioned land” ruined by greed and inattention.

His words tremble with rage, and I would dearly love to ignore them, deny our role in the threat, call this a wholly natural disaster. But even if we dismiss our own role, we are still facing a crisis. We are still on the verge of losing the world that has sheltered and awed us.

Those little plastic dinosaurs? A future civilization might craft something similar in the image of Homo sapiens.

In the end, extinction is apolitical. And while nature’s resilience is lovely to contemplate, particular life forms do get wiped out forever. No scaly lycopsids grow in my backyard, and the dragonflies that hover over the nearby lake are just shimmering points of colored light. Our planet suffers life-shattering traumas just surely as we do. And if we try to escape that knowledge by retreating into the past, we will crash right through to the present, because all of it is connected.

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