by Deborah Blum
“I know that some naturalists rely a lot on the thousands of centuries that they pile up with a stroke of the pen,” Cuvier responded dismissively. Eventually he was called upon to compose a eulogy for Lamarck, which he did very much in the spirit of burying rather than praising. Lamarck, according to Cuvier, was a fantasist. Like the “enchanted palaces of our old romances,” his theories were built on “imaginary foundations,” so that while they might “amuse the imagination of a poet,” they could not “for a moment bear the examination of anyone who has dissected a hand, a viscus, or even a feather.”
Having dismissed transformisme, Cuvier was left with a gaping hole. He had no account of how new organisms could appear, or any explanation for how the world could have come to be populated by different groups of animals at different times. This doesn’t seem to have bothered him. His interest, after all, was not in the origin of species but in their demise.
The very first time he spoke about the subject, Cuvier intimated that he knew the driving force behind extinction, if not the exact mechanism. In his lecture on elephants, he proposed that the mastodon, the mammoth, and the Megatherium had all been wiped out “by some kind of catastrophe.” Cuvier hesitated to speculate about the precise nature of the calamity—“It is not for us to involve ourselves in the vast field of conjectures that these questions open up”—but at that point he seems to have believed that one disaster would have sufficed.
Later, as his list of extinct species grew, his position changed. There had, he decided, been multiple cataclysms. “Life on earth has often been disturbed by terrible events,” he wrote. “Living organisms without number have been the victims of these catastrophes.”
Like his view of transformisme, Cuvier’s belief in cataclysm fit with—indeed, could be said to follow from—his convictions about anatomy. Since animals were functional units, ideally suited to their circumstances, there was no reason, in the ordinary course of events, that they should die out. Not even the most devastating events known to occur in the contemporary world—volcanic eruptions, say, or forest fires—were sufficient to explain extinction; confronted with such changes, organisms simply moved on and survived. The changes that had caused extinctions must therefore have been of a much greater magnitude—so great that animals had been unable to cope with them. That such extreme events had never been observed by him or any other naturalist was another indication of nature’s mutability: in the past, it had operated differently—more intensely and more savagely—than it did at present.
“The thread of operations is broken,” Cuvier wrote. “Nature has changed course, and none of the agents she employs today would have been sufficient to produce her former works.” Cuvier spent several years studying the rock formations around Paris—together with a mineralogist friend, he produced the first stratigraphic map of the Paris Basin—and here, too, he saw signs of cataclysmic change. The rocks showed that, at various points, the region had been submerged. The shifts from one environment to another—from marine to terrestrial or, at some points, from marine to freshwater—had, Cuvier decided, “not been slow at all”; rather, they had been brought about by those sudden “revolutions” on the surface of the earth. The latest of these revolutions must have occurred relatively recently, for traces of it were still everywhere apparent. This event, Cuvier believed, lay just beyond the edge of recorded history; he observed that many ancient myths and texts, including the Old Testament, allude to some sort of crisis—usually a deluge—that preceded the present order.
Cuvier’s ideas about a globe wracked periodically by cataclysm proved to be nearly as influential as his original discoveries. His major essay on the subject, which was published in Paris in 1812, was almost immediately reprinted in English and exported to America. It also appeared in German, Swedish, Italian, and Russian. But a good deal was lost or, at least, misinterpreted in translation. Cuvier’s essay was pointedly secular. He cited the Bible as merely one of many ancient texts, alongside the Hindu Vedas and the Shujing. This sort of ecumenism was unacceptable to the Anglican clergy who made up the faculty at institutions like Oxford, and when the essay was translated into English it was construed by Buckland and others as offering proof of Noah’s flood.
By now the empirical grounds of Cuvier’s theory have largely been disproved. The physical evidence that convinced him of a “revolution” just prior to recorded history (and that the English interpreted as proof of the Deluge) was in reality debris left behind by the last glaciation. The stratigraphy of the Paris Basin reflects not sudden “irruptions” of water but, rather, gradual changes in sea level and the effects of plate tectonics. On all these matters, Cuvier was, we now know, wrong.
Yet his wildest-sounding claims have turned out to be surprisingly accurate. Cataclysms happen. Nature does on occasion “change course,” and at such moments it is as if the “thread of operations” has been broken. The contemporary term for these cataclysms is “mass extinctions,” and the geological record suggests that in the past half-billion years, there have been five major ones and a dozen or more lesser ones. In the most severe of the so-called Big Five, at the end of the Permian period, some 250 million years ago, something like 90 percent of all species died off, and multicellular life came perilously close to being obliterated altogether. In the most recent, at the end of the Cretaceous, the dinosaurs were wiped out, along with the mosasaurs, the pterosaurs, the plesiosaurs, the ammonites, and two-thirds of all families of mammals, all in what, geologically speaking, amounted to an instant.
Meanwhile, as far as the American mastodon is concerned, Cuvier was to an almost uncanny extent correct. He decided that the beast had disappeared 5,000 or 6,000 years ago, in the same “revolution” that had killed off the mammoth and the Megatherium. Actually, the American mastodon vanished around 13,000 years ago, in a wave of disappearances that has become known as the megafauna extinction. This wave coincided with the spread of modern humans, and, increasingly, is understood to have been a result of it. Humans are now so rapidly transforming the planet—changing the atmosphere, altering the chemistry of the oceans, reshuffling the biosphere—that many scientists argue that we’ve entered a whole new geological epoch: the Anthropocene. In this sense, the crisis that Cuvier discerned just beyond the edge of recorded history was us.
II
The Geological Society of London, known to its members as the Geol Soc (pronounced “gee-ahl sock”), was founded in 1807, over dinner in a Covent Garden tavern. Geology was at that point a brand-new science, a circumstance reflected in the society’s goals, which were to stimulate “zeal” for the discipline and to induce participants “to adopt one nomenclature.” There followed long, often spirited debates on matters such as where to fix the borders of the Devonian period. “Though I don’t much care for geology,” one visitor to the society’s early meetings noted, “I do like to see the fellows fight.”
The Geol Soc is now headquartered in a stone mansion not far from Piccadilly Circus. On the outside the style of the mansion is Palladian; inside, it leans more toward midcentury public library. Much of the place is wrapped in plastic, owing to a construction project that never quite seems to reach completion. Near the reception desk, behind a green velvet curtain, hangs a copy of the first geological map of Britain, which was published in 1815 by William Smith. (Smith’s British biographer has called the map “one of the classics of English science”; his American counterpart has pronounced it “the map that changed the world.”) At the top of the stairs, there’s a reading room with a brass chandelier, a few armchairs, some scuffed tables, and a broken coffee machine.
On a sunny morning not long ago, Jan Zalasiewicz, a stratigrapher and longtime society member, was sitting in the reading room, wishing the coffee machine were functional so that he could make a cup of tea. Zalasiewicz is a slight, almost elfin man with shaggy graying hair and narrow blue eyes. He had come down to London that morning from his home in Nottinghamshire to give a visitor a tour. His perspective on the Geol S
oc, and on the city more generally, was, he had to admit, idiosyncratic.
“This building has never been considered as a rock before,” he observed. “But it is just as much made of geology as anything you would find out in the field.
“Clearly, very few of these objects will survive Pompeii style,” he went on, gesturing, with a faraway look in his eyes, toward the chairs, the tables, the magazine racks, and the coffee machine. “But they won’t simply disappear. They’ll break down into rubble, and the rubble will be washed away. But even the rubble that’s been washed away will have its own character, its own signal.” He swiveled to take in the windows (mostly silica) and the paneling (made of wood). “Potentially, everything here is fossilizable,” he said.
Walter White–like, Zalasiewicz leads a double life. By day he’s an expert on a group of ancient marine organisms known as graptolites. Zalasiewicz deeply admires graptolites, which thrived and diversified in the early Paleozoic, some 500 million years ago, only to be very nearly wiped out in a catastrophic extinction event. Present him with a fossilized graptolite and he can tell you at a glance which biozone of the Silurian period it belongs to.
In his off-hours, Zalasiewicz is a provocateur or, to be more British about it, “a scientific hooligan.” He has more or less invented a new discipline, which might be called the stratigraphy of the future. It is based on a simple, if disturbing, premise: humans are so radically refashioning the planet—leveling so many forests, eliminating so many creatures that once occupied those forests, transporting so many other creatures around the globe, and burning through such vast quantities of fossil fuels to keep the whole enterprise going—that we may well end up producing a catastrophe comparable in scale to the one that laid waste to the graptolites. Already, Zalasiewicz is convinced, the geology of the planet has been permanently altered. The signal that will be left behind by our cities, our carbon emissions, and our potentially fossilizable detritus is strong enough, he maintains, that even a moderately competent stratigrapher, at a distance of 100 million years or so, should be able to tell that something extraordinary happened in what to us represents the present. “We have already left a record that is now indelible,” he has written.
In recognition of the ways that, collectively, we are all world-changers, Zalasiewicz believes that an adjustment in nomenclature is called for. Officially, our epoch is the Holocene, but Zalasiewicz believes it would probably be more accurate to say that we have entered the Anthropocene. He is trying to persuade his colleagues to formally consider this new term. He hopes to bring the matter to a vote of the International Commission on Stratigraphy in 2016. If he has his way, every geology textbook in the world will instantly become obsolete.
The path led up a hill, across a stream, back across the stream, and past the carcass of a sheep, which looked deflated, like a lost balloon. The hill was bright green but treeless; generations of the sheep’s relatives had kept anything from growing much above muzzle height. As far as I was concerned, it was raining. But in the Southern Uplands of Scotland, I was told, this counted only as a light drizzle, or smirr.
Zalasiewicz and I and two of his colleagues from the British Geological Survey had driven for more than five hours to get to the Uplands from the Survey’s headquarters near Nottingham. We were hiking to a spot called Dob’s Linn, where, according to an old ballad, the Devil himself was pushed over a precipice by a pious shepherd named Dob. By the time we reached the cliff, the smirr seemed to be smirring harder. There was a view over a waterfall, which crashed down into a narrow valley. A few yards farther up the path loomed a jagged outcropping of rock. It was striped vertically, like a referee’s jersey, in bands of light and dark. Zalasiewicz set his rucksack down on the soggy ground and adjusted his red rain jacket. He pointed to one of the dark-colored stripes. “Bad things happened in here,” he told me.
Much as Civil War buffs visit Gettysburg, stratigraphers are drawn to Dob’s Linn. It’s one of those rare places where, owing to an accident of plate tectonics, a major turning point in life’s history is visible right on the surface of the earth. In this case, the event is the end-Ordovician extinction, which occurred some 440 million years ago. In addition to nearly knocking out the graptolites, it killed off something like 80 percent of the planet’s species. (“Had the list of survivors been one jot different,” Richard Fortey, a British paleontologist and a recent president of the Geol Soc, has observed, “then so would the world today.”) Not coincidentally, Dob’s Linn is also a great place to find graptolites.
To the naked eye, graptolite fossils look a bit like scratches and a bit like hieroglyphics. (“Graptolite” comes from the Greek, meaning “written rock”; the term was coined by Linnaeus, who dismissed graptolites as mineral encrustations trying to pass themselves off as the remnants of animals.) Viewed through a hand lens, they often prove to have lovely, evocative shapes; one species suggests a feather, another a lyre, a third the frond of a fern. Graptolites were colonial animals. Each one, known as a zooid, built itself a tiny, tubular shelter, known as a theca, that was attached to its neighbor’s, like a row house. A single graptolite fossil thus represents a whole community, which drifted or, more probably, swam along as a single entity, feeding off even smaller plankton. Zalasiewicz lent me a hammer, and one of the graptolites I hacked out of the rock face had been preserved with peculiar clarity. It was shaped like a set of false eyelashes, but very small, as if for a Barbie. Zalasiewicz told me—doubtless exaggerating—that I had found a “museum-quality specimen.” I pocketed it.
Graptolites had a habit—endearing from a stratigrapher’s point of view—of speciating, spreading out, and dying off, all in relatively short order. Zalasiewicz likened them to Natasha, the tender heroine of War and Peace. They were, he told me, “delicate, nervous, and very sensitive to things around them.” This makes them useful “index fossils”—successive species can be used to identify successive layers of rock.
Once Zalasiewicz showed me what to look for at Dob’s Linn, I too could see that “bad things” happened here. The dark stripes were shale; in them, graptolites were plentiful and varied. This indicated that there was nothing alive to consume the animals once they’d died and sunk to the sea floor. Soon I’d collected so many that the pockets of my jacket were sagging. Many of the fossils were variations on the letter V, with two arms branching away from a central node. Some looked like zippers, others like wishbones. Still others had arms growing off their arms, like tiny trees.
The lighter stone—also shale—was barren, with barely a graptolite to be found in it. Paradoxically, this was a sign of a healthy ocean floor, with lots of scavengers living in the muck. The transition from one state to another—from gray stone to black, from no graptolites to many—appears to have occurred suddenly and, according to Zalasiewicz, did occur suddenly. “The change here from gray to black marks a tipping point, if you like, from a habitable sea floor to an uninhabitable one,” Zalasiewicz said. “And one might have seen that in the span of a human lifetime.” He described this transition as “Cuvierian.”
Zalasiewicz’s colleagues from the British Geological Survey, Dan Condon and Ian Millar, had come to Dob’s Linn to collect samples from the various stripes. (Zalasiewicz also worked for many years at the BGS; he now teaches at the University of Leicester.) The samples, they hoped, would contain tiny crystals of zircon, which, after some complicated chemical manipulations, would allow them to date the layers of rock quite precisely. Millar, who grew up in Scotland, at first claimed to be undaunted by the smirr. But after a while even he admitted that it was pouring. Rivulets of mud were cascading down the face of the outcropping, compromising the samples. It was decided that we would have to come back the following day. The geologists packed up their gear and we squished back down the trail to the car. Zalasiewicz had made reservations at a bed-and-breakfast in the nearby town of Moffat. The town’s attractions, I had read, included Britain’s narrowest hotel and a bronze sheep.
The idea that
the world can change suddenly and drastically—“in the span of a human lifetime”—is very old and, at the same time, very new. To the early members of the Geol Soc, the role of catastrophe in the earth’s history was self-evident. These men—and they were, of course, all men—had read the great nineteenth-century French naturalist Georges Cuvier, who interpreted the fossil record as a chronicle of recurring tragedy. (When the Napoleonic Wars ended in 1815, Cuvier was made an honorary Geol Soc member.)
“Life on earth has often been disturbed by terrible events,” Cuvier wrote. “Living organisms without number have been the victims of these catastrophes.”
Cuvier’s view of life was challenged by Charles Lyell, another of the nineteenth century’s most influential naturalists. According to Lyell, who served as the Geol Soc’s fourteenth president and also as its twenty-first, the earth was capable of changing only very gradually. The way to understand the distant past was to look at the present. Since no one had ever seen the kind of cataclysm that Cuvier invoked, it was unscientific or, to use Lyell’s term, “unphilosophical,” to imagine that such events took place. If it appeared from the fossil record that the world had changed abruptly, Lyell maintained, this just went to show how little the record was to be trusted.
Among the early converts to Lyell’s view was Charles Darwin. In On the Origin of Species, Darwin acknowledged that there were points in the earth’s history when it appeared that “whole families or orders” had suddenly been exterminated. But like Lyell, he took this as evidence that “wide intervals of time” were unaccounted for. Had the evidence of these intervals not been lost, it would have shown “much slow extermination.” He wrote, “So profound is our ignorance, and so high our presumption, that we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world!”
