“As often as I have seen beds of mud, sand, and shingle, accumulated to the thickness of many thousand feet, I have felt inclined to exclaim that causes, such as the present rivers and the present beaches, could never have ground down and produced such masses. But, on the other hand, when listening to the rattling noise of these torrents, and calling to mind that whole races of animals have passed away from the face of the earth, and that during this whole period, night and day, these stones have gone rattling onwards in their course, I have thought to myself, can any mountains, any continent, withstand such waste?”
It is the dawn of a new geological age. A teeming swarm of Homo sapiens gathers on the banks of an estuary at the edge of the North American continent. The glaciers have retreated; the seas have risen more than 400 feet since the last ice age; and the gleaming new steel-and-glass hives of Manhattan rise up from the marshes.
Looming over the confident city, just across the Hudson River, is the sheer cliff face of the Palisades. The gigantic columns of basalt sit in unimpressed, stony silence, as they have for 200 million years. These cliffs, covered in highway weeds and graffiti, are monuments to an ancient apocalypse. They’re made of magma that once fed burbling fountains of lava at the surface – lava that once smothered the planet from Nova Scotia to Brazil.
The eruptions flooded the atmosphere with carbon dioxide at the end of the Triassic period, roasting the planet and acidifying the oceans for thousands of years. Brief blasts of volcanic smog punctuated this super-greenhouse with cold. The runaway volcanism covered more than 4 million square miles of the planet and killed off more than three-quarters of animal life on earth in a geological instant.
I struggled to keep up with Columbia University paleontologist Paul Olsen as he bounded up the scraggly path leading from the banks of the Hudson to the base of the Palisades. In front of us, smothered under this enormous wall of now-solid magma, were the remains of a quarter-billion-year-old lake bottom, complete with exquisitely preserved fish and reptile fossils. Behind us, faintly droning, was the skyline of New York City.
I asked Olsen whether the city across the river would be preserved for future geologists to discover, like this peaceful Triassic diorama at the bottom of the rocks. He turned to consider the scenery. “You might have a layer of stuff,” he said dismissively, “but it’s not a sedimentary basin, so eventually it would erode away to nothing. You’d have bits that would make it out into the ocean and would be buried and might show up—some bottle caps, maybe. There would be some pretty heavy-duty isotopic signals. But the subway system wouldn’t fossilize or anything. It all would erode away fairly quickly.”
It is from this disorienting perspective that geologists operate: to them, millions of years run together, seas divide continents, then drain away, and great mountain ranges erode to sand in moments. It’s an outlook that’s necessary to cultivate if one wants to get a handle on the staggering depths of geological time, which recedes behind us hundreds of millions of years and stretches out before us to infinity.
If Olsen’s attitude seems dispassionate in the extreme, it’s a symptom of a lifetime’s immersion in Earth’s history, which is both vast beyond comprehension and, in some exceedingly rare moments, tragic beyond words. Animal life has been all but destroyed in sudden, planetwide exterminations five times in Earth’s history. These are the so-called Big Five mass extinctions, commonly defined as any event in which more than half of the earth’s species go extinct in fewer than a million years or so.
We now know that many of these mass extinctions seem to have happened much more quickly. Thanks to fine-scale geochronology, we know that some of the most extreme die-offs in earth history lasted only a few thousand years, at the very most, and may have been much quicker.
A more qualitative way to describe something like this is Armageddon. The most famous member of this gloomy fraternity is the End-Cretaceous mass extinction, which notably took out the (nonbird) dinosaurs 66 million years ago.
But the End-Cretaceous is only the most recent mass extinction in the history of life. The volcanic doomsday whose stony embers I saw exposed in the cliffs next to Manhattan – a disaster that brought down an alternate universe of distant crocodile relatives and global coral reef systems – struck 135 million years before the death of the dinosaurs.
This disaster and the three other major mass extinctions that preceded it are invisible, for the most part, in the public imagination, long overshadowed by the downfall of T.rex. This isn’t entirely without reason. For one thing, dinosaurs are the most charismatic characters in the fossil record, celebrities of earth history that paleontologists who work on earlier, more neglected periods scoff at as preening oversized monsters. As such, dinosaurs hog most of the popular press spared for paleontology. In addition, the dinosaurs were wiped out in spectacular fashion, with their final moments punctuated by the impact of a 6-mile-long asteroid in Mexico.
But if it was a space rock that did in the dinosaurs, it seems to have been a unique disaster. Some astronomers outside the field push the idea that periodic asteroid strikes caused each of the planet’s other four mass extinctions, but this hypothesis has virtually no support in the fossil record. In the past three decades, geologists have scoured the fossil record looking for evidence of devastating asteroid impacts at those mass extinctions, and have come up empty.
The most dependable and frequent administrators of global catastrophe, it turns out, are dramatic changes to the climate and the ocean, driven by the forces of geology itself. The three biggest mass extinctions in the past 300 million years are all associated with giant floods of lava on a continental scale – the sorts of eruptions that beggar the imagination.
Life on earth is resilient, but not infinitely so: the same volcanoes that are capable of turning whole continents inside out can also produce climatic and oceanic chaos worthy of the apocalypse. In these rare eruptive cataclysms the atmosphere becomes supercharged with volcanic carbon dioxide, and during the worst mass extinction of all time, the planet was rendered a hellish, rotting sepulcher, with hot, acidifying oceans starved of oxygen.
But in other earlier mass extinctions, it might have been neither volcanoes nor asteroids at fault. Instead, some geologists say that plate tectonics, and perhaps even biology itself, conspired to suck up CO2 and poison the oceans. While continental-scale volcanism sends CO2 soaring, in these earlier, somewhat more mysterious extinctions, carbon dioxide might have instead plummeted, imprisoning the earth in an icy crypt. Rather than spectacular collisions with other heavenly bodies, it has been these internal shocks to the earth system that have most frequently knocked the planet off course. Much of the planet’s misfortune, it seems, is homegrown.
Luckily, these uber-catastrophes are comfortingly rare, having struck only five times in the more than half a billion years since complex life emerged (occurring, roughly, 445, 374, 252, 201, and 66 million years ago).
But it’s a history that has frightening echoes in our own world – which is undergoing changes not seen for tens of millions, or even hundreds of millions, of years. “It’s pretty clear that times of high carbon dioxide – and especially times when carbon dioxide levels rapidly rose – coincided with the mass extinctions,” writes University of Washington paleontologist and End-Permian mass extinction expert Peter Ward. “Here is the driver of extinction.” As civilization is busy demonstrating, supervolcanoes aren’t the only way to get lots of carbon buried in the rocks out into the atmosphere in a hurry.
Today humanity busies itself by digging up hundreds of millions of years of carbon buried by ancient life and ignites it all at once at the surface, in pistons and power plants – the vast, diffuse metabolism of modern civilization. If we see this task to completion and burn it all – supercharging the atmosphere with carbon like an artificial supervolcano – it will indeed get very hot, as it has before. The hottest heat waves experienced today will become the average, while future heat waves will push many parts of the world into uncharted territory, taking on a new menace that will surpass the hard limits of human physiology.
If this comes to pass, the planet will return to a condition that, though utterly alien to us, has made many appearances in the fossil record. But warm times aren’t necessarily a bad thing. The dinosaur-haunted Cretaceous was significantly richer in atmospheric CO2, and that period was consequently much warmer than today. But when climate change or ocean chemistry changes have been sudden, the result has been devastating for life. In the worst of times, the earth has been all but ruined by these climate paroxysms as lethally hot continental interiors, acidifying, anoxic oceans, and mass death swept over the planet.
This is the revelation of geology in recent years that presents the most worrying prospect for modern society. The five worst episodes in earth history have all been associated with violent changes to the planet’s carbon cycle.
Over time, this fundamental element moves back and forth between the reservoirs of biology and geology: volcanic carbon dioxide in the air is captured by carbon-based life in the sea, which dies and becomes carbonate limestone on the seafloor. When that limestone is thrust down into the earth, it’s cooked and the carbon dioxide is spit out by volcanoes into the air once more. And on and on. This is why it’s a cycle. But events like sudden, extraordinarily huge injections of carbon dioxide into the atmosphere and oceans can short-circuit this chemistry of life. This prospect is one reason why past mass extinctions have become such a vogue topic of late in the research community. Most of the scientists I spoke with over the course of reporting this book were interested in the planet’s history of near-death experiences, not just to answer an academic question, but also to learn, by studying the past, how the planet responds to exactly the sorts of shocks we’re currently inflicting on it.
This ongoing conversation in the research community is strikingly at odds with the one taking place in the broader culture. Today much of the discussion about carbon dioxide’s role in driving climate change makes it seem as though the link exists only in theory, or in computer models. But our current experiment – quickly injecting huge amounts of carbon dioxide into the atmosphere – has in fact been run many times before in the geological past, and it never ends well.
In addition to the unanimous and terrifying projections of climate models, we also have a case history of carbon dioxide-driven climate change in the planet’s geologic past that we would be well advised to consult. These events can be instructive, even diagnostic, for our modern crises, like the patient who presents to his doctor with chest pains after a history of heart attacks. But there’s a risk of stretching the analogy too far: Earth has been many different planets over its lifetime, and though in some salient and worrying ways our modern planet and its future prospects echo some of the most frightening chapters in its history, in many other ways our modern biocrises represent a one-off, a unique disruption in the history of life.
Thankfully, we still have time. Though we’ve proven to be a destructive species, we have not produced anything even close to the levels of wanton destruction and carnage seen in previous planetary cataclysms. These are absolute worst-case scenarios.
The epitaph for humanity does not yet have to include the tragic indictment of having engineered the sixth major mass extinction in earth history.
In a world sometimes short on it, this is good news.
Like many kids, I came to the topic of mass extinctions early. As the son of a children’s librarian, I grew up in a house that was often brimming with cardboard boxes of books – the surplus of the most recent book fair. Perhaps to my mom’s frustration, I would pass over copies of Where the Red Fern Grows and The Giver and go straight for the pop-ups. Tyrannosaurs and cycads leapt from the page as I obsessed over the strange Latinate names and the even stranger creatures they described. Here an artist had decided to spangle a bizarre-looking animal called parasaurolophus in neon, while another illustrator had oviraptors draped in zebra stripes. It was irresistible: a world of sci-fi monsters that had actually existed.
But Disney’s Fantasia illuminated for me as a child an even stranger fact about this world: that it had all occurred in the past, to the music of Stravinsky’s orchestra, the dinosaurs lurched to their deaths over a cauterized landscape, and the world ended in tragedy. It was no more. Later obsessions, like the movie and book versions of Jurassic Park, only reinforced for me the melancholy of living in a world that had lost its dragons.
In the past few decades, geologists have started filling in the rough sketches of the Big Five mass extinctions with gruesome detail, but the story has largely eluded the public imagination. Our conception of history tends to stretch back only a few thousand years at most, and typically only a few hundred. This is a scandalously shortsighted appreciation of what came before – like reading only the last sentence of a book and claiming to understand what’s in the rest of the library.
That the planet has nearly died five times over the past 500 million years is a remarkable fact, and as we, as a civilization, push the chemistry and temperature of the climate-ocean system into territory not seen for tens of millions of years, we should be curious about where the hard limits are. Just how bad could it get?
The history of mass extinctions provides the answer to this question. Visiting Earth’s turbulent and unfamiliar past provides a possible window into our future. Forgotten worlds spill from the sides of highways, from beach cliffs, and from the edges of baseball fields, hiding in plain sight. This was perhaps the central revelation to me as I began to accompany paleontologists in the field to learn more about the five major mass extinctions. I didn’t have to talk my way onto expeditions to the Arctic or the Gobi Desert to find the strange stratigraphy of long-past worlds. We live on a palimpsest of earth history.
The lesson of geology is that we inherit this world – this “antique planet with a brand new civilization,” as Carl Sagan put it – from countless vanished ages. To see the world through the lens of geology is to see the world for the first time.
In North America, fossils are found not only in the mythic Southwest and in exposed Arctic mountainsides but hidden under Walmart parking lots, in quarries, and in road cuts on the interstate. Underneath Cincinnati is an endless fossil bas-relief of tropical sea life in the early oceans of the Ordovician period, which ended half a billion years ago in the second worst extinction in Earth’s history.
There are plesiosaurs in riverbanks in downtown Austin, saber-toothed cats in Los Angeles, and killer crocs from the Triassic under Dulles Airport outside of Washington, DC. In Cleveland’s riverbanks are the armor-plated remains of a guillotine-mouthed, titanic fish from the Devonian period, 360 million years old. The wreckage from the Big Five mass extinctions lies on remote, verdant islands in the Canadian Maritimes, on icier patches in Antarctica and Greenland, under Mayan temples in Mexico, strewn across the desolation of South Africa’s Karoo Desert, and on the edges of farmland in China.
But this legacy of disaster is also visible next to skyscrapers in New York City and in the shales of the Midwest (so profitable for frackers and environmental fundraisers alike) that were forged in the chaos of the Late Devonian mass extinctions. Rising out of the deserts of West Texas are the Guadalupe Mountains, a haunted monument built almost entirely from ancient sea animals in the full bloom of life before the single worst chapter in the planet’s history: a period of crises capped by a carbon dioxide–driven global warming catastrophe that killed off 90 percent of life on Earth.
Life on earth constitutes a remarkably thin glaze of interesting chemistry on an otherwise unremarkable, cooling ball of stone, hovering like a sand grain in an endless ocean of empty space. This sheet of life that coats the planet – a feature of our world that has been almost miraculously durable over Earth’s history – is perhaps unique in the galaxy. But viewed through the lens of mass extinctions, it’s also remarkably fragile: when crises push the planet outside a narrow set of surface conditions, it has been nearly sterilized.
Much has been made of the search beyond our planet for spectacular external threats like asteroids, but we should be equally vigilant about the subtler threats from within. As the roster of lifeless planets in our solar system attests, the agreeable chemistry and conditions on the surface of the earth are incredibly unusual. And as the history of mass extinctions demonstrates, they’re not a given.
In researching these ancient disasters, I expected to find a story as neat and tidy as the one about the asteroid that killed the dinosaurs. What I found instead was a frontier of discovery with much left to be unearthed, and a story still largely obscured by the fog of deep time. In my travels I became acquainted with whole worlds, still called “Earth”, that I had scarcely known existed, brought low by a suite of world-ending forces far subtler, but just as ominous, as asteroids.
This book is a woefully incomplete testament to the ingenuity of those who have labored to piece this fractured, and still unfinished – puzzle together, as well as a survey of the unfamiliar geography of deep time that surrounds us. It’s also an exploration of the turbulent centuries to come and the long-term prospects for life on this strangely hospitable but vulnerable planet that hurtles through a perilous universe.
After hiking the Palisades, Olsen and I hit up one of the dozens of Vietnamese pho restaurants in the nearby Fort Lee neighborhood, where a snarl of highways branch out of the George Washington Bridge. Contemplating the history of the region and the ancient hellscape created by the rocks underneath us, I found it difficult not to wonder about the future. Currently the carbon dioxide concentration in the atmosphere hovers at around 400 parts per million (ppm) – probably the highest it’s been since the middle of the Pliocene epoch 3 million years ago.
What will life be like on the planet at 1,000 parts per million, which some climate scientists and policymakers project for the coming decades if we continue to take a business-as-usual approach to emissions? “The last time anything like that occurred, we had no polar ice at all and sea levels were hundreds of feet higher,” Olsen said, noting that crocodiles and lemur-relatives inhabited the tropical northern shores of Canada. “Ocean temperatures in the tropics were possibly 40 degrees Celsius on average, which would be completely alien to us now. “The interior of continents,” he continued, “endured persistently lethal conditions.”
I put the question a little more bluntly, asking him whether we might be at the beginning of another mass extinction. “Yeah,” he said, resting his chopsticks for a moment. “Yeah. Although the one that would be obvious in the fossil record happened over a 50,000-year interval from the time that humans spread out of Africa and wiped out all the megafauna. That’s the one that will show up like gangbusters in the fossil record. Someday they might say that the industrial spread of humans was just the coup de grâce.”
The Ends of the World. Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth’s Past Mass Extinctions.
by Peter Brannen.
get it at Amazon.com