Environmental science

Read The Sixth Extinction, pages 81-161



Pinguinus impennis

The word “catastrophist” was coined in 1832 by William Whewell, one of the first presidents of the Geological Society of London, who also bequeathed to English “anode,” “cathode,” “ion,” and “scientist.” Although the term would later pick up pejorative associations, which stuck to it like burrs, this was not Whewell’s intention. When he proposed it, Whewell made it clear that he considered himself a “catastrophist,” and that most of the other scientists he knew were catastrophists too. Indeed, there was really only one person he was acquainted with ” “whom the label did not fit, and that was an up-and-coming young geologist named Charles Lyell. For Lyell, Whewell came up with yet another neologism. He called him a “uniformitarian.”

“Lyell had grown up in the south of England, in the sort of world familiar to fans of Jane Austen. He’d then attended Oxford and trained to become a barrister. Failing eyesight made it difficult for him to practice law, so he turned to the natural sciences instead. As a young man, Lyell made several trips to the Continent and became friendly with Cuvier, at whose house he dined often. He found the older man to be personally “very obliging”—Cuvier allowed him to make casts of several famous fossils to take back with him to England—but Cuvier’s vision of earth history Lyell regarded as thoroughly unpersuasive.”

“When Lyell looked (admittedly myopically) at the rock outcroppings of the British countryside or at the strata of the Paris basin or at the volcanic islands near Naples, he saw no evidence of cataclysm. In fact, quite the reverse: he thought it unscientific (or, as he put it, “unphilosophical”) to imagine that change in the world had ever occurred for different reasons or at different rates than it did in the present day. According to Lyell, every feature of the landscape was the result of very gradual processes operating over countless millennia—processes like sedimentation, erosion, and vulcanism, which were all still readily observable. For generations of geology students, Lyell’s thesis would be summed up as “The present is the key to the past.”

“As far as extinction was concerned, this, too, according to Lyell, occurred at a very slow pace—so slow that, at any given time, in any given place, it would not be surprising were it to go unnoticed. The fossil evidence, which seemed to suggest that species had at various points died out en masse, was a sign that the record was unreliable. Even the idea that the history of life had a direction to it—first reptiles, then mammals—was mistaken, another faulty inference drawn from inadequate data. All manner of organisms had existed in all eras, and those that had apparently vanished for good could, under the right circumstances, pop up again. Thus “the huge iguanodon might reappear in the woods, and the ichthyosaur in the sea, while the pterodactyle might flit again through umbrageous groves of tree-ferns.” It is clear, Lyell wrote, “that there is no foundation in geological facts for the popular theory of the successive development of the animal and vegetable world.”

“Lyell published his ideas in three thick volumes, Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth’s Surface by Reference to Causes Now in Operation. The work was aimed at a general audience, which embraced it enthusiastically. A first print run of forty-five hundred copies quickly sold out, and a second run of nine thousand was ordered up. (In a letter to his fiancée, Lyell boasted that this represented “at least 10 times” as many books as any other English geologist had ever sold.) Lyell became something of a celebrity—the Steven Pinker of his generation—and when he spoke in Boston more than four thousand people tried to get tickets.”

“for the sake of clarity (and a good read), Lyell had caricatured his opponents, making them sound a great deal more “unphilosophical” than they actually were. They returned the favor. A British geologist named Henry De la Beche, who had a knack for drawing, poked fun at Lyell’s ideas about eternal return. He produced a cartoon showing Lyell in the form of a nearsighted ichthyosaur, pointing to a human skull and lecturing to a group of giant reptiles.”

“You will at once perceive,” Professor Ichthyosaurus tells his pupils in the caption, “that the skull before us belonged to some of the lower order of animals; the teeth are very insignificant, the power of the jaws trifling, and altogether it seems wonderful how the creature could have procured food.” De la Beche called the sketch “Awful Changes.”

“AMONG the readers who snapped up the Principles was Charles Darwin. Twenty-two years old and fresh out of Cambridge, Darwin had been invited to serve as a sort of gentleman’s companion to the captain of the HMS Beagle, Robert FitzRoy. The ship was headed to South America to survey the coast and resolve various mapping discrepancies that hindered navigation. (The Admiralty was particularly interested in finding the best approach to the Falkland Islands, which the British had recently assumed control of.) The voyage, which would last until Darwin was twenty-seven, would take him from Plymouth to Montevideo, through the Strait of Magellan, up to the Galápagos Islands, across the South Pacific to Tahiti, on to New Zealand, Australia, and Tasmania, across the Indian Ocean to Mauritius, around the Cape of Good Hope, and back again to South America. In the popular imagination, the journey is usually seen as the time when Darwin, encountering a wild assortment of giant tortoises, seafaring lizards, and finches with beaks of every imaginable shape and size, discovered natural selection. In fact, Darwin developed his theory only after his return to England, when other naturalists sorted out the jumble of specimens he had shipped back.

“It would be more accurate to describe the voyage of the Beagle as the period when Darwin discovered Lyell. Shortly before the ship’s departure, FitzRoy presented Darwin with a copy of volume one of the Principles. Although he was horribly seasick on the first leg of the journey (as he was on many subsequent legs), Darwin reported that he read Lyell “attentively” as the ship headed south. The Beagle made its first stop at St. Jago—now Santiago—in the Cape Verde Islands, and Darwin, eager to put his new knowledge to work, spent several days collecting specimens from its rocky cliffs. One of Lyell’s central claims was that some areas of the earth were gradually rising, just as others were gradually subsiding. (Lyell further contended that these phenomena were always in balance, so as to “preserve the uniformity of the general relations of the land and sea.”) St. Jago seemed to prove his point. “ The island was clearly volcanic in origin, but it had several curious features, including a ribbon of white limestone halfway up the dark cliffs. The only way to explain these features, Darwin concluded, was as evidence of uplift. The very first place “which I geologised convinced me of the infinite superiority of Lyell’s views,” he would later write. So taken was Darwin with volume one of the Principles that he had volume two shipped to him for pickup at Montevideo. Volume three, it seems, caught up with him in the Falklands.”

“While the Beagle was sailing along the west coast of South America, Darwin spent several months exploring Chile. He was resting after a hike one afternoon near the town of Valdivia when the ground beneath him began to wobble, as if made of jelly. “One second of time conveys to the mind a strange idea of insecurity, which hours of reflection could never create,” he wrote.” “Several days after the earthquake, arriving in Concepción, Darwin found the entire city had been reduced to rubble. “It is absolutely true, there is not one house left habitable,” he reported. The scene was the “most awful yet interesting spectacle” he’d ever witnessed. A series of surveying measurements that FitzRoy took around Concepción’s harbor showed that the quake had elevated the beach by nearly eight feet. Once again, Lyell’s Principles appeared to be rather spectacularly confirmed. Given enough time, Lyell argued, repeated quakes could raise an entire mountain chain many thousands of feet high.”

“he more Darwin explored the world, the more Lyellian it seemed to him to be. Outside the port of Valparaiso, he found deposits of marine shells far above sea level. These he took to be the result of many episodes of elevation like the one he’d just witnessed. “I have always thought that the great merit of the Principles was that it altered the whole tone of one’s mind,” he would later write. (While in Chile, Darwin also discovered a new and rather remarkable species of frog, which became known as the Chile Darwin’s frog. Males of the species incubated their tadpoles in their vocal sacs. Recent searches have failed to turn up any Chile Darwin’s frogs, and the species is now believed to be extinct.)”

“Toward the end of the Beagle’s voyage, Darwin encountered coral reefs. These provided him with his first major breakthrough, a startling idea that would ease his entrée into London’s scientific circles. Darwin saw that the key to understanding coral reefs was the interplay between biology and geology. If a reef formed around an island or along a continental margin that was slowly sinking, the corals, by growing slowly upward, could maintain their position relative to the water. Gradually, as the land subsided, the corals would form a barrier reef. If, eventually, the land sank away entirely, the reef would form an atoll.”

“Darwin’s account went beyond and to a certain extent contradicted Lyell’s; the older man had hypothesized that reefs grew from the rims of submerged volcanoes. But Darwin’s ideas were so fundamentally Lyellian in nature that when, upon his return to England, Darwin presented them to Lyell, the latter was delighted. As the historian of science Martin Rudwick has put it, Lyell “recognized that Darwin had out-Lyelled him.”

“One biographer summed up Lyell’s influence on Darwin as follows: “Without Lyell there would have been no Darwin.” Darwin himself, after publishing his account of the voyage of the Beagle and also a volume on coral reefs, wrote, “I always feel as if my books came half out of Lyell’s brains.”

“LYELL, who saw change occurring always and everywhere in the world around him, drew the line at life. That a species of plant or animal might, over time, give rise to a new one he found unthinkable, and he devoted much of the second volume of the Principles to attacking the idea, at one point citing Cuvier’s mummified cat experiment in support of his objections.”

“Lyell’s adamant opposition to transmutation, as it was known in London, is almost as puzzling as Cuvier’s. New species, Lyell realized, regularly appeared in the fossil record. But how they originated was an issue he never really addressed, except to say that probably each one had begun with “a single pair, or individual, where an individual was sufficient” and multiplied and spread out from there. This process, which seemed to depend on divine or at least occult intervention, was clearly at odds with the precepts he had laid out for geology. Indeed, as one commentator observed, it seemed to require “exactly the kind of miracle” that Lyell had rejected.”

“With his theory of natural selection, Darwin once again “out-Lyelled” Lyell. Darwin recognized that just as the features of the inorganic world—deltas, river valleys, mountain chains—were brought into being by gradual change, the organic world similarly was subject to constant flux. Ichthyosaurs and plesiosaurs, birds and fish and—most discomfiting of all—humans had come into being through a process of transformation that took place over countless generations. This process, though imperceptibly slow, was, according to Darwin, still very much going on; in biology, as in geology, the present was the key to the past. In one of the most often-quoted passages of On the Origin of Species, Darwin wrote:

It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers.”

“Natural selection eliminated the need for any sort of creative miracles. Given enough time for “every variation, even the slightest” to accumulate, new species would emerge from the old. Lyell this time was not so quick to applaud his protégé’s work. He only grudgingly accepted Darwin’s theory of “descent with modification,” so grudgingly that his stance seems to have eventually ruined their friendship.”

“Darwin’s theory about how species originated doubled as a theory of how they vanished. Extinction and evolution were to each other the warp and weft of life’s fabric, or, if you prefer, two sides of the same coin. “The appearance of new forms and the disappearance of old forms” were, Darwin wrote, “bound together.” Driving both was the “struggle for existence,” which rewarded the fit and eliminated the less so.”

“The theory of natural selection is grounded on the belief that each new variety, and ultimately each new species, is produced and maintained by having some advantage over those with which it comes into competition; and the consequent extinction of less favoured forms almost inevitably follows.

“Darwin used the analogy of domestic cattle. When a more vigorous or productive variety was introduced, it quickly supplanted other breeds. In Yorkshire, for example, he pointed out, “it is historically known that the ancient black cattle were displaced by the long-horns,” and that these were subsequently “swept away” by the short-horns, “as if by some murderous pestilence.”

Darwin stressed the simplicity of his account. Natural selection was such a powerful force that none other was needed. Along with miraculous origins, world-altering catastrophes could be dispensed with. “The whole subject of the extinction of species has been involved in the most gratuitous mystery,” he wrote, implicitly mocking Cuvier.”

“From Darwin’s premises, an important prediction followed. If extinction was driven by natural selection and only by natural selection, the two processes had to proceed at roughly the same rate. If anything, extinction had to occur more gradually.

“The complete extinction of the species of a group is generally a slower process than their production,” he observed at one point.”

“No one had ever seen a new species produced, nor, according to Darwin, should they expect to. Speciation was so drawn out as to be, for all intents and purposes, unobservable. “We see nothing of these slow changes in progress,” he wrote. It stood to reason that extinction should have been that much more difficult to witness. And yet it wasn’t. In fact, during the years Darwin spent holed up at Down House, developing his ideas about evolution, the very last individuals of one of Europe’s most celebrated species, the great auk, disappeared. What’s more, the event was painstakingly chronicled by British ornithologists. Here Darwin’s theory was directly contradicted by the facts, with potentially profound implications.”

“THE Icelandic Institute of Natural History occupies a new building on a lonely hillside outside Reykjavik. The building has a tilted roof and tilted glass walls and looks a bit like the prow of a ship. It was designed as a research facility, with no public access, which means that a special appointment is needed to see any of the specimens in the institute’s collection. These specimens, as I learned on the day of my own appointment, include: a stuffed tiger, a stuffed kangaroo, and a cabinet full of stuffed birds of paradise.”

“The reason I’d arranged to visit the institute was to see its great auk. Iceland enjoys the dubious distinction of being the bird’s last known home, and the specimen I’d come to look at was killed somewhere in the country—no one is sure of the exact spot—in the summer of 1821. The bird’s carcass was purchased by a Danish count, Frederik Christian Raben, who had come to Iceland expressly to acquire an auk for his collection (and had nearly drowned in the attempt). “Raben took the specimen home to his castle, and it remained in private hands until 1971, when it came up for auction in London. The Institute of Natural History solicited donations, and within three days Icelanders contributed the equivalent of ten thousand British pounds to buy the auk back. (One woman I spoke to, who was ten years old at the time, recalled emptying her piggy bank for the effort.) Icelandair provided two free seats for the homecoming, one for the institute’s director and the other for the boxed bird.”

“Guðmundur Guðmundsson, who’s now the institute’s deputy director, had been assigned the task of showing me the auk. Guðmundsson is an expert on foraminifera, tiny marine creatures that form intricately shaped shells, known as “tests.” On our way to see the bird, we stopped at his office, which was filled with boxes of little glass tubes, each containing a sampling of tests that rattled like sprinkles when I picked it up. Guðmundsson told me that in his spare time he did translating. A few years ago he had completed the first Icelandic rendering of On the Origin of Species. He’d found Darwin’s prose quite difficult—“sentences inside sentences inside sentences”—and the book, Uppruni Tegundanna, had not sold well, perhaps because so many Icelanders are fluent in English.

We made our way to the storeroom for the institute’s collection. The stuffed tiger, wrapped in plastic, looked ready to lunge at the stuffed kangaroo. The great auk—Pinguinus impennis—was standing off by itself, in a specially made Plexiglas case. It was perched on a fake rock, next to a fake egg.”

“As the name suggests, the great auk was a large bird; adults grew to be more than two and a half feet tall. The auk could not fly—it was one of the few flightless birds of the Northern Hemisphere—and its stubby wings were almost comically undersized for its body. The auk in the case had brown feathers on its back; probably these were black when the bird was alive but had since faded. “UV light,” Guðmundsson said gloomily. “It destroys the plumage.” The auk’s chest feathers were white, and there was a white spot just beneath each eye. The bird had been stuffed with its most distinctive feature—its large, intricately grooved beak—tipped slightly into the air. This lent it a look of mournful hauteur.

“Guðmundsson explained that the great auk had been on display in Reykjavik until 2008, when the institute was restructured by the Icelandic government. At that point, another agency was supposed to create a new home for the bird, but various mishaps, including Iceland’s financial crisis, had prevented this from happening, which is why Count Raben’s auk was sitting on its fake rock in the corner of the storeroom. On the rock, there was a painted inscription, which Guðmundsson translated for me: THE BIRD WHO IS HERE FOR SHOW WAS KILLED IN 1821. IT IS ONE OF THE FEW GREAT AUKS THAT STILL EXIST.”

“N its heyday, which is to say, before humans figured out how to reach its nesting grounds, the great auk ranged from Norway over to Newfoundland and from Italy to Florida, and its population probably numbered in the millions. When the first settlers arrived in Iceland from Scandinavia, great auks were so common that they were regularly eaten for dinner, and their remains have been found in the tenth-century equivalent of household trash. While I was in Reykjavik, I visited a museum built over the ruins of what’s believed to be one of the most ancient structures in Iceland—a longhouse constructed out of strips of turf. “According to one of the museum’s displays, the great auk was “easy prey” for Iceland’s medieval inhabitants. In addition to a pair of auk bones, the display featured a video re-creation of an early encounter between man and bird. In the video, a shadowy figure crept along a rocky shore toward a shadowy auk. When he drew close enough, the figure pulled out a stick and clubbed the animal over the head. The auk responded with a cry somewhere between a honk and a grunt. I found the video grimly fascinating “cinating and watched it play through a half a dozen times. Creep, clobber, squawk. Repeat.”

“As best as can be determined, great auks lived much as penguins do. In fact, great auks were the original “penguins.” They were called this—the etymology of “penguin” is obscure and may or may not be traced to the Latin pinguis, meaning “fat”—by European sailors who encountered them in the North Atlantic. Later, when subsequent generations of sailors met similar-colored flightless birds in the Southern Hemisphere, they used the same name, which led to much confusion, since auks and penguins belong to entirely different families. (Penguins constitute their own family, while auks are members of the family that includes puffins and guillemots; genetic analysis has shown that razorbills are the great auk’s closest living relatives.)”

“Like penguins, great auks were fantastic swimmers—eyewitness accounts attest to the birds’ “astonishing velocity” in the water—and they spent most of their lives at sea. But during breeding season, in May and June, they waddled ashore in huge numbers, and here lay their vulnerability. Native Americans clearly hunted the great auk—one ancient grave in Canada was found to contain more than a hundred great auk beaks—as did paleolithic Europeans: great auk bones have been found at archaeological sites in, among other places, Denmark, Sweden, Spain, Italy, and Gibraltar. By the time the first settlers got to Iceland, many of its breeding sites had already been plundered and its range was probably much reduced. Then came the wholesale slaughter.”

“Lured by the rich cod fishery, Europeans began making regular voyages to Newfoundland in the early sixteenth century. Along the way, they encountered a slab of pinkish granite about fifty acres in area, which rose just above the waves. In the spring, the slab was covered with birds, standing, in a manner of speaking, shoulder to shoulder. Many of these were gannets and guillemots; the rest were great auks. The slab, about forty miles off Newfoundland’s northeast coast, became known as the Isle of Birds or, in some accounts, Penguin Island; today it is known as Funk Island. Toward the end of a long transatlantic journey, when provisions were running low, fresh meat was prized, and the ease with which auks could be picked off the slab was soon noted. In an account from 1534, the French explorer Jacques Cartier wrote that some of the Isle of Birds’ inhabitants were “as large as geese.”

“They are always in the water, not being able to fly in the air, inasmuch as they have only small wings … with which … they move as quickly along the water as the other birds fly through the air. And these birds are so fat it is marvellous. In less than half an hour we filled two boats full of them, as if they had been stones, so that besides them which we did not eat fresh, every ship did powder and salt five or six barrels full of them.

“A British expedition that landed on the island a few years later found it “full of great foules.” The men drove a “great number of the foules” into their ships and pronounced the results to be quite tasty—“very good and nourishing meat.” A 1622 account by a captain named Richard Whitbourne describes great auks being driven onto boats “by hundreds at a time as if God had made the innocency of so poor a creature to become such an admirable instrument for the sustenation of Man.”

“Over the next several decades, other uses for the great auk were found besides “sustenation.” (As one chronicler observed, “the great auks of Funk Island were exploited in every way that human ingenuity could devise.”) Auks were used as fish bait, as a source of feathers for stuffing mattresses, and as fuel. Stone pens were erected on Funk Island—vestiges of these are still visible today—and the birds were herded into the enclosures until someone could find time to butcher them. Or not. According to an English seaman named Aaron Thomas, who sailed to Newfoundland on the HMS Boston:

“If you come for their Feathers you do not give yourself the trouble of killing them, but lay hold of one and pluck the best of the Feathers. You then turn the poor Penguin adrift, with his skin half naked and torn off, to perish at his leisure.”

“There are no trees on Funk Island, and hence nothing to burn. This led to another practice chronicled by Thomas.”

“You take a kettle with you into which you put a Penguin or two, you kindle a fire under it, and this fire is absolutely made of the unfortunate Penguins themselves. Their bodys being oily soon produce a Flame.”

“It’s been estimated that when Europeans first landed at Funk Island, they found as many as a hundred thousand pairs of great auks tending to a hundred thousand eggs. (Probably great auks produced only one egg a year; these were about five inches long and speckled, Jackson Pollock–like, in brown and black.) Certainly the island’s breeding colony must have been a large one to persist through more than two centuries of depredation. By the late seventeen hundreds, though, the birds’ numbers were in sharp decline. The feather trade had become so lucrative that teams of men were spending the entire summer on Funk, scalding and plucking. In 1785, George Cartwright, an English trader and explorer, observed of these teams: “The destruction which they have made is incredible.” If a stop were not soon put to their efforts, he predicted, the great auk would soon “be diminished to almost nothing.”

“Whether the teams actually managed to kill off every last one of the island’s auks or whether the slaughter simply reduced the colony to the point that it became vulnerable to other forces is unclear. (Diminishing population density may have made survival less likely for the remaining individuals, a phenomenon that’s known as the Allee effect.) In any event, the date that’s usually given for the extirpation of the great auk from North America is 1800. Some thirty years later, while working on The Birds of America, John James Audubon traveled to Newfoundland in search of great auks to paint from life. He couldn’t find any, and for his illustration had to make do with a stuffed bird from Iceland that had been acquired by a dealer in London. In his description of the great auk, Audubon wrote that it was “rare and accidental on the banks of Newfoundland” and that it was “said to breed on a rock on that island,” a curious contradiction since no breeding bird can be said to be “accidental.”

“ONCE the Funk Island birds had been salted, plucked, and deep-fried into oblivion, there was only one sizable colony of great auks left in the world, on an island called the Geirfuglasker, or great auk skerry, which lay about thirty miles off southwestern Iceland’s Reykjanes Peninsula. Much to the auk’s misfortune, a volcanic eruption destroyed the Geirfuglasker in 1830. This left the birds one solitary refuge, a speck of an island known as Eldey. By this point, the great auk was facing a new threat: its own rarity. Skins and eggs were avidly sought by gentlemen, like Count Raben, who wanted to fill out their collections. It was in the service of such enthusiasts that the very last known pair of auks was killed on Eldey in 1844.”

“Before setting out for Iceland, I’d decided that I wanted to see the site of the auk’s last stand. Eldey is only about ten miles off the Reykjanes Peninsula, which is just south of Reykjavik. But getting out to the island proved to be way more difficult to arrange than I’d imagined. Everyone I contacted in Iceland told me that no one ever went there. Eventually, a friend of mine “who’s from Iceland got in touch with his father, who’s a minister in Reykjavik, who contacted a friend of his, who runs a nature center in a tiny town on the peninsula called Sandgerði. The head of the nature center, Reynir Sveinsson, in turn, found a fisherman, Halldór Ármannsson, who said he’d be willing to take me, but only if the weather was fair; if it was rainy or windy, the trip would be too dangerous and nausea-inducing, and he wouldn’t want to risk it.”

“Fortunately, the weather on the day we’d fixed turned out to be splendid. I met Sveinsson at the nature center, which features an exhibit on a French explorer, Jean-Baptiste Charcot, who died when his ship, the infelicitously named Pourquoi-Pas, sunk off Sandgerði in 1936. We walked over to the harbor and found Ármannsson loading a chest onto his boat, the Stella. He explained that inside the chest was an extra life raft. “Regulations,” he shrugged. Ármannsson had also brought along his fishing partner and a cooler filled with soda and cookies. He seemed pleased to be making a trip that didn’t involve cod.”

“We motored out of the harbor and headed south, around the Reykjanes Peninsula. It was clear enough that we could see the snow-covered peak of Snæfellsjökull, more than sixty miles away. (To English speakers, Snæfellsjökull is probably best known as the spot where in Jules Verne’s A Journey to the Center of the Earth the hero finds a tunnel through the globe.) Eldey, being much shorter than Snæfellsjökull, was not yet visible. Sveinsson explained that Eldey’s name means “fire island.” He said that although he’d spent his entire life in the area, he’d never before been out to it. He’d brought along a fancy camera and was shooting pictures more or less continuously.”

“As Sveinnson snapped away, I chatted with Ármannsson inside the Stella’s small cabin. I was intrigued to see that he had dramatically different colored eyes, one blue and one hazel. Usually, he told me, he fished for cod using a long line that extended six miles and trailed twelve thousand hooks. The baiting of the hooks was his father’s job, and it took nearly two days. A good catch could weigh more than seven metric tons. Often Ármannsson slept on the Stella, which was equipped with a microwave and two skinny berths.”

“After a while, Eldey appeared on the horizon. The island looked like the base of an enormous column, or like a giant pedestal waiting for an even more gigantic statue. When we got within maybe a mile, I could see that the top of the island, which from a distance appeared flat, was actually tilted at about a ten-degree angle. We were approaching from the shorter end, so we could look across the entire surface. It was white and appeared to be rippling. As we got closer, I realized that the ripples were birds—so many that they seemed to blanket the island—and when we got even closer, I could see that the birds were gannets—elegant creatures with long necks, cream-colored heads, and tapered beaks. Sveinsson explained that Eldey was “home to one of the world’s largest colonies of northern gannets—some thirty thousand pairs. He pointed out a pyramid-like structure atop the island. This was a platform for a webcam that Iceland’s environmental agency had set up. It was supposed to stream a live feed of the gannets to bird-watchers, but it had not functioned as planned.”

“The birds do not like this camera,” Sveinsson said. “So they fly over it and shit on it.” The guano from thirty thousand gannet pairs has given the island what looks like a coating of vanilla frosting.”

“Because of the gannets, and perhaps also because of the island’s history, visitors are not allowed to step onto Eldey without special (and hard-to-obtain) permits. When I first learned this, I was disappointed, but when we got right up to the island and I saw the way the sea beat against the cliffs, I felt relieved.”

“THE last people to see great auks alive were around a dozen Icelanders who made the trip to Eldey by rowboat. They set out one evening in June 1844, rowed through the night, and reached the island the following morning. With some difficulty, three of the men managed to clamber ashore at the only possible landing spot: a shallow shelf of rock that extends from the island to the northeast. (A fourth man who was supposed to go with them refused to on the grounds that it was too dangerous.) By this point the island’s total auk population, probably never very numerous, appears to have consisted of a single pair of birds and one egg. On catching sight of the humans, the birds tried to run, but they were too slow. Within minutes, the Icelanders had captured the auks and strangled them. The egg, they saw, had been cracked, presumably in the course of the chase, so they left it behind. Two of the men were able to jump back into the boat; the third had to be hauled through the waves with a rope.”

“The details of the great auks’ last moments, including the names of the men who killed the birds—Sigurður Iselfsson, ”

“Ketil Ketilsson, and Jón Brandsson—are known because fourteen years later, in the summer of 1858, two British naturalists traveled to Iceland in search of auks. The older of these, John Wolley, was a doctor and an avid egg collector; the younger, Alfred Newton, was a fellow at Cambridge and soon to be the university’s first professor of zoology. The pair spent several weeks on the Reykjanes Peninsula, not far from the site of what is now Iceland’s international airport, and during that time, they seem to have talked to just about everyone who had ever seen an auk, or even just heard about one, including several of the men who’d made the 1844 expedition. “he pair spent several weeks on the Reykjanes Peninsula, not far from the site of what is now Iceland’s international airport, and during that time, they seem to have talked to just about everyone who had ever seen an auk, or even just heard about one, including several of the men who’d made the 1844 expedition. The pair of birds that had been killed in that outing, they discovered, had been sold to a dealer for the equivalent of about nine pounds. The birds’ innards had been sent to the Royal Museum in Copenhagen; no one could say what had happened to the skins. (Subsequent detective work has traced the skin of the female to an auk now on display at the Natural History Museum of Los Angeles.)”

“Wolley and Newton hoped to get out to Eldey themselves. Wretched weather prevented them. “Boats and men were engaged, and stores laid in, but not a single opportunity occurred when a landing would have been practicable,” Newton would later write. “It was with heavy hearts that we witnessed the season wearing away.”

“Wolley died shortly after the pair returned to England. For Newton, the experience of the trip would prove to be life-altering. He concluded that the auk was gone—“for all practical purposes therefore we may speak of it as a thing of the past”—and he developed what one biographer referred to as a “peculiar attraction” to “extinct and disappearing faunas.” Newton realized that the birds that bred along Britain’s long coast were also in danger; he noted that they were being gunned down for sport in great numbers.”

“The bird that is shot is a parent,” he observed in an address to the British Association for the Advancement of Science. “We take advantage of its most sacred instincts to waylay it, and in depriving the parent of life, we doom the helpless offspring to “the most miserable of deaths, that by hunger. If this is not cruelty, what is?” Newton argued for a ban on hunting during breeding season, and his lobbying resulted in one of the first laws aimed at what today would be called wildlife protection: the Act for the Preservation of Sea Birds.”

“AS it happens, Darwin’s first paper on natural selection appeared in print just as Newton was returning home from Iceland. The paper, in the Journal of the Proceedings of the Linnean Society, had—with Lyell’s help—been published in a rush soon after Darwin had learned that a young naturalist named Alfred Russel Wallace was onto a similar idea. (A paper by Wallace appeared in the same issue of the Journal.) Newton read Darwin’s essay very soon after it came out, staying up late into the night to finish it, and he immediately became a convert. “It came to me like the direct revelation of a higher power,” he later recalled, “and I awoke next morning with the consciousness that there was an end of all the mystery in the simple phrase, ‘Natural Selection.’” He had, he wrote to a friend, developed a case of “pure and unmitigated Darwinism. “A few years later, Newton and Darwin became correspondents—at one point Newton sent Darwin a diseased partridge’s foot that he thought might be of interest to him—and eventually the two men paid social calls on each other.”

“Whether the subject of the great auk ever came up in their conversations is unknown. It is not mentioned in Newton and Darwin’s surviving correspondence, nor does Darwin allude to the bird or its recent demise in any of his other writings. But Darwin had to be aware of human-caused extinction. In the Galápagos, he had personally witnessed, if not exactly a case of extinction in action, then something very close to it.”

“Darwin’s visit to the archipelago took place in the fall of 1835, nearly four years into the voyage of the Beagle. On Charles Island—now Floreana—he met an Englishman named Nicholas Lawson, who was the Galápagos’s acting governor as well as the warden of a small, rather miserable penal colony. Lawson was full of useful information. Among the facts he related to Darwin was that on each of the islands in the Galápagos the tortoises had different-shaped shells. On this basis, Lawson claimed that he could “pronounce from which island any tortoise may have been brought.” Lawson also told Darwin that the tortoises’ days were numbered. “ The islands were frequently visited by whaling ships, which carried the huge beasts off as portable provisions. Just a few years earlier, a frigate visiting Charles Island had left with two hundred tortoises stowed in its hold. As a result, Darwin noted in his diary, “the numbers have been much reduced.” By the time of the Beagle’s visit, tortoises had become so scarce on Charles Island that Darwin, it seems, did not see a single one. Lawson predicted that Charles’s tortoise, known today by “the scientific name Chelonoidis elephantopus, would be entirely gone within twenty years. In fact, it probably disappeared in fewer than ten. (Whether Chelonoidis elephantopus was a distinct species or a subspecies is still a matter of debate.)”

“Darwin’s familiarity with human-caused extinction is also clear from On the Origin of Species. In one of the many passages in which he heaps scorn on the catastrophists, he observes that animals inevitably become rare before they become extinct: “we know this has been the progress of events with those animals which have been exterminated, either locally or wholly, through man’s agency.” It’s a brief allusion and, in its brevity, suggestive. Darwin assumes that his readers are familiar with such “events” and already habituated to them. He himself seems to find nothing remarkable or troubling about this. But human-caused extinction is of course troubling for many reasons, some of which have to do with Darwin’s own theory, and it’s puzzling that a writer as shrewd and self-critical as Darwin shouldn’t have noticed this.”

“n the Origin, Darwin drew no distinction between man and other organisms. As he and many of his contemporaries recognized, this equivalence was the most radical aspect of his work. Humans, just like any other species, were descended, with modification, from more ancient forebears. Even those qualities that seemed to set people apart—language, wisdom, a sense of right and wrong—had evolved in the same manner as other adaptive traits, such as longer beaks or sharper incisors. At the heart of Darwin’s theory, as one of his biographers has put it, is “the denial of humanity’s special status.”

“And what was true of evolution should also hold for extinction, since according to Darwin, the latter was merely a side effect of the former. Species were annihilated, just as they were created, by “slow-acting and still existing causes,” which is to say, through competition and natural selection; to invoke any other mechanism was nothing more than mystification. But how, then, to make sense of cases like the great auk or the Charles Island tortoise or, to continue the list, the dodo or the Steller’s sea cow? These animals had obviously not been done in by a rival species gradually evolving some competitive advantage. They had all been killed off by the same species, and all quite suddenly—in the case of the great auk and the Charles Island tortoise over the course of Darwin’s own lifetime. Either there had to be a separate category for human-caused extinction, in which case people really did deserve their “special status” as a creature outside of nature, or space in the natural order had to be made for cataclysm, in which case, Cuvier—distressingly—was right.”



Discoscaphites jerseyensis”

“The hill town of Gubbio, about a hundred miles north of Rome, might be described as a municipal fossil. Its streets are so narrow that on many of them not even the tiniest Fiat has room to maneuver, and its gray stone piazzas look much as they did in Dante’s era. (In fact, it was a powerful Gubbian, installed as lord mayor of Florence, who engineered Dante’s exile, in 1302.) If you visit in winter, as I did, when the tourists are gone, the hotels shuttered, and the town’s picture-book palace deserted, it almost seems as if Gubbio has fallen under a spell and is waiting to be awoken.”

“Just beyond the edge of town a narrow gorge leads off to the northeast. The walls of the gorge, which is known as the Gola del Bottaccione, consist of bands of limestone that run in diagonal stripes. Long before people settled the region—long before people existed—Gubbio lay at the bottom of a clear, blue sea. The remains of tiny marine creatures rained down on the floor of that sea, building up year after year, century after century, millennium after millennium. In the uplift that created the Apennine Mountains, the limestone was elevated and tilted at a forty-five-degree angle. To walk up the gorge today is thus to travel, layer by layer, through time. In the space of a few hundred yards, you can cover almost a hundred million years.”

“The Gola del Bottaccione is now a tourist destination in its own right, though for a more specialized crowd. It is here that in the late nineteen-seventies, a geologist named Walter Alvarez, who had come to study the origins of the Apennines, ended up, more or less by accident, rewriting the history of life. In the gorge, he discovered the first traces of the giant asteroid that ended the Cretaceous period and caused what may have been the worst day ever on planet earth. By the time the dust—in this case, literal as much as figurative—had settled, some three-quarters of all species had been wiped out.

“The evidence of the asteroid’s impact lies in a thin layer of clay about halfway up the gorge. Sightseers can park at a turnoff constructed nearby. There’s also a little kiosk explaining, in Italian, the site’s significance. The clay layer is easy to spot. It’s been gouged out by hundreds of fingers, a bit like the toes of the bronze St. Peter in Rome, worn down by the kisses of pilgrims. The day I visited was gray and blustery, and I had the place to myself. I wondered what had prompted all that fingering. Was it simple curiosity? A form of geologic rubbernecking? Or was it something more empathetic: the desire to make contact—however attenuated—with a lost world? I, too, of course, had to stick my finger in. I poked around in the groove and scraped out a pebble-sized piece of clay. It was the color of worn brick and the consistency of dried mud. I put it in an old candy wrapper and stuck it in my pocket—my own little chunk of planetary disaster.”

“WALTER Alvarez came from a long line of distinguished scientists. His great-grandfather and grandfather were both noted physicians, and his father, Luis, was a physicist at the University of California-Berkeley. But it was his mother who took him for long walks in the Berkeley hills and got him interested in geology. Walter attended graduate school at Princeton, then went to work for the oil industry. (He was living in Libya when Muammar Gaddafi took over the country in 1969.) A few years later he got a research post at the Lamont-Doherty Earth Observatory, across the Hudson from Manhattan. At the time, what’s sometimes called the “plate tectonics revolution” was sweeping through the profession, and just about everyone at Lamont got swept up in it.”

“Alvarez decided to try to figure out how, on the basis of plate tectonics, the Italian peninsula had come into being. Key to the project was a kind of reddish limestone, known as the scaglia “rosso, which can be found, among other places, in the Gola del Bottaccione. The project moved forward, got stuck, and shifted direction. “In science, sometimes it’s better to be lucky than smart,” he would later say of these events. Eventually, he found himself working in Gubbio with an Italian geologist named Isabella Premoli Silva, who was an expert on foraminifera.”

“Foraminifera, or “forams” for short, are the tiny marine creatures that create little calcite shells, or tests, which drift down to the ocean floor once the animal inside has died. The tests have a distinctive shape, which varies from species to species; some look (under magnification) like beehives, others like braids or bubbles or clusters of grapes. Forams tend to be widely distributed and abundantly preserved, and this makes them extremely useful as index fossils: on the basis of which species of forams are found in a given layer of rock, an expert like Silva can tell the rock’s age. As they worked their way up the Gola del Bottaccione, Silva pointed out to Alvarez a curious sequence. The limestone from the last stage of the Cretaceous period contained diverse, abundant, and relatively large forams, many as big as grains of sand. Directly above that, there was a layer of clay about half an inch thick with no forams in it. Above the clay there was limestone with more forams, but these belonged to only a handful of species, all of them very tiny and all totally different from the larger ones below.”

“Alvarez had been schooled in, to use his phrase, a “kind of hard-core uniformitarianism.” He’d been trained to believe, after Lyell and Darwin, that the disappearance of any group of organisms had to be a gradual process, with one species slowly dying out, then another, then a third, and so on. Looking at the sequence in the Gubbio limestone, though, he saw something different. The many species of forams in the lower layer seemed to disappear suddenly and all more or less at the same time; the whole process, Alvarez would later recall, certainly “looked very abrupt.” Then there was the odd matter of timing. The king-sized forams appeared to vanish right around the point the last of the dinosaurs were known to have died off. This struck Alvarez as more than just a coincidence. He thought it would be interesting to know exactly how much time that half-inch of clay represented.”

“In 1977, Alvarez got a job at Berkeley, where his father, Luis, was still working, and he brought with him to California his samples from Gubbio. While Walter had been studying plate tectonics, Luis had won a Nobel Prize. He’d also developed the first linear proton accelerator, invented a new kind of bubble chamber, designed several innovative radar systems, and codiscovered tritium. Around Berkeley, Luis had become known as the “wild idea man.” Intrigued by a debate over whether there were treasure-filled chambers inside Egypt’s second-largest pyramid, he’d at one point designed a test that required installing a muon detector in the desert. (The detector showed that the pyramid was, in fact, solid rock.) At another point, he’d become interested in the Kennedy assassination and had performed an experiment that involved wrapping cantaloupes in shipping tape and shooting them with a rifle. (The experiment demonstrated that the movement of the president’s head after he was hit was consistent with the findings of the Warren Commission.) “When Walter told his father about the puzzle from Gubbio, Luis was fascinated. It was Luis who came up with the wild idea of clocking the clay using the element iridium.”

“Iridium is extremely rare on the surface of the earth but much more common in meteorites. In the form of microscopic grains of cosmic dust, bits of meteorites are constantly raining down on the planet. Luis reasoned that the longer it had taken the clay layer to accumulate, the more cosmic dust would have fallen; thus the more iridium it would contain. He contacted a Berkeley colleague, Frank Asaro, whose lab was one of the few with the right kind of equipment for this sort of analysis. Asaro agreed to run tests on a dozen samples, though he said he very much doubted anything would come of it. Walter gave him some limestone from above the clay layer, some from below it, and some of the clay itself. Then he waited. Nine months later, he got a call. There was something seriously wrong with the samples from the clay layer. The amount of iridium in them was off the charts.”

“No one knew what to make of this. Was it a weird anomaly, or something more significant? Walter flew to Denmark, to collect some late-Cretaceous sediments from a set of limestone cliffs known as Stevns Klint. At Stevns Klint, the end of the Cretaceous period shows up as a layer of clay that’s jet black and smells like dead fish. When the stinky Danish samples were analyzed, they, too, revealed astronomical levels of iridium. A third set of samples, from the South Island of New Zealand, also showed an iridium “spike” right at the end of the Cretaceous.”

“Luis, according to a colleague, reacted to the news “like a shark smelling blood”; he sensed the opportunity for a great discovery. The Alvarezes batted around theories. But all the ones they could think of either didn’t fit the available data or were ruled out by further tests. Then, finally, after almost a year’s worth of dead ends, they arrived at the impact hypothesis. On an otherwise ordinary day sixty-five million years ago, an asteroid six miles wide collided with the earth. Exploding on contact, it released energy on the order of a hundred million megatons of TNT, or more than a million of the most powerful H-bombs ever tested. Debris, including iridium from the pulverized asteroid, spread around the globe. Day turned to night, and temperatures plunged. A mass extinction ensued.

The Alvarezes wrote up the results from Gubbio and Stevns Klint and sent them, along with their proposed explanation, to Science. “I can remember working very hard to make that paper just as solid as it could possibly be,” Walter told me.”

“THE Alvarezes’ paper, “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction,” was published in June 1980. It generated lots of excitement, much of it beyond the bounds of paleontology. Journals in disciplines ranging from clinical psychology to herpetology reported on the Alvarezes’ findings, and soon the idea of an end-Cretaceous asteroid was picked up by magazines like Time and Newsweek. One commentator observed that “to connect the dinosaurs, creatures of interest to but the veriest dullards, with a spectacular extraterrestrial event” seemed “like one of those plots a clever publisher might concoct to guarantee sales.” Inspired by the impact hypothesis, a group of astrophysicists led by Carl Sagan decided to try to model the effects of an all-out war and came up with the concept of “nuclear winter,” which, in turn, generated its own wave of media coverage.

But among professional paleontologists, the Alvarezes’ idea and in many cases the Alvarezes themselves were reviled. “The apparent mass extinction is an artifact of statistics and poor understanding of the taxonomy,” one paleontologist told the New York Times.”

“But among professional paleontologists, the Alvarezes’ idea and in many cases the Alvarezes themselves were reviled. “The apparent mass extinction is an artifact of statistics and poor understanding of the taxonomy,” one paleontologist told the New York Times.

“The arrogance of those people is unbelievable,” a second asserted. “They know next to nothing about how real animals evolve, live, and become extinct. But despite their ignorance, the geochemists feel that all you have to do is crank up some fancy machine and you’ve revolutionized science.”

“Unseen bolides dropping into an unseen sea are not for me,” a third declared.”

“The Cretaceous extinctions were gradual and the catastrophe theory is wrong,” yet another paleontologist stated. But “simplistic theories will continue to come along to seduce a few scientists and enliven the covers of popular magazines.” Curiously enough, the Times’ editorial board decided to weigh in on the matter. “Astronomers should leave to astrologers the task of seeking the cause of earthly events in the stars,” the paper admonished.

To understand the vehemence of this reaction, it helps to go back, once again, to Lyell. In the fossil record, mass extinctions stand out, so much so that the very language that’s used to describe earth’s history is derived from them. In 1841, John Phillips, a contemporary of Lyell’s who succeeded him as president of the Geological Society of London, divided life into three chapters. He called the first the Paleozoic, from the Greek for “ancient life,” the second the Mesozoic, meaning “middle life,” and the third the Cenozoic, “new life.” Phillips fixed as the dividing point between the Paleozoic and the Mesozoic what would now be called the end-Permian extinction, and between the Mesozoic and the Cenozoic, the end-Cretaceous event. (In geologic parlance, the Paleozoic, Mesozoic, and Cenozoic are “eras,” and each era comprises several “periods”; the Mesozoic, for example, spans the Triassic, the Jurassic, and the Cretaceous.) The fossils from the three eras were so different that Phillips thought they represented distinct acts of creation.

“Lyell was well aware of these breaks in the fossil record. In the third volume of the Principles of Geology, he noted a “chasm” between the plants and animals found in rocks from the late Cretaceous period and those found directly above, at the start of the Tertiary period (which is now technically known as the beginning of the Paleogene). For instance, late Cretaceous deposits contained the remains of numerous species of belemnites—squid-like creatures that left behind fossils shaped like bullet casings. But belemnite fossils were never found in more recent deposits. The same pattern held for ammonites, and for “rudist bivalves—mollusks that formed immense reefs. (Rudists have been described as oysters pretending to be corals.) To Lyell, it was simply impossible, or “unphilosophical,” to imagine that this “chasm” represented what it seemed to—sudden and dramatic global change. So, in a rather neat bit of circular reasoning, he asserted that the faunal gap was just a gap in the fossil record. After comparing the life forms on both sides of the supposed gap, Lyell concluded that the unaccounted-for interval must have been a long one, roughly equivalent to all the time that had passed since the record had resumed. Using today’s dating methods, the lacuna he was positing amounts to some sixty-five million years.”

“Darwin, too, was well informed about the discontinuity at the end of the Cretaceous. In the Origin, he observed that the disappearance of the ammonites seemed to be “wonderfully sudden.” And, just like Lyell, he dismissed the ammonites and what they seemed to be saying. “For my part,” he observed,”

“I look at the natural geological record, as a history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.”

“The fragmentary nature of the record meant that the semblance of abrupt change was just that: “With respect to the apparently sudden extermination of whole families or orders,” it must be remembered, he wrote, that “wide intervals of time” were probably unaccounted for. Had the evidence of these intervals not been lost, it would have shown “much slow extermination.” In this way, Darwin continued the Lyellian project of turning the geologic evidence on its head. “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!” he declared.”

“Darwin’s successors inherited the “much slow extermination” problem. The uniformitarian view precluded sudden or sweeping change of any kind. But the more that was learned about the fossil record, the more difficult it was to maintain that an entire age, spanning tens of millions of years, had somehow or other gone missing. This growing tension led to a series of increasingly tortured explanations. Perhaps there had been some sort of “crisis” at the close of the Cretaceous, but it had to have been a very slow crisis. Maybe the losses at the end of the period did constitute a “mass extinction.” But mass extinctions were not to be confused with “catastrophes.” The same year that the Alvarezes published their paper in Science, George Gaylord Simpson, at the time probably the world’s most influential paleontologist, wrote that the “turnover” at the end of the Cretaceous should be regarded as part of “a long and essentially continuous process.”

In the context of “hard-core uniformitarianism,” the impact hypothesis was worse than wrong. The Alvarezes were claiming to explain an event that hadn’t happened—one that couldn’t have happened. It was like peddling patent medicine for a fictitious illness. A few years after father and son published their hypothesis, an informal survey was conducted at a meeting of the Society of Vertebrate Paleontology. A majority of those surveyed said they thought some sort of cosmic collision might have taken place. But only one in twenty thought it had anything to do with the extinction of the dinosaurs. One paleontologist at the meeting labeled the Alvarez hypothesis “codswallop.”

“MEANWHILE, evidence for the hypothesis continued to accumulate.

The first independent corroboration came in the form of tiny grains of rock known as “shocked quartz.” Under high magnification, shocked quartz exhibits what look like scratch marks, the result of bursts of high pressure that deform the crystal structure. Shocked quartz was first noted at nuclear test sites and subsequently found in the immediate vicinity of impact craters. In 1984, grains of shocked quartz were discovered in a layer of clay from the Cretaceous-Tertiary, or K-T, boundary in eastern Montana. (K is used as the abbreviation for Cretaceous because C was already taken by the Carboniferous; today, the border is formally known as the Cretaceous-Paleogene, or K-Pg, boundary.)”

“The next clue showed up in south Texas, in a curious layer of end-Cretaceous sandstone that seemed to have been produced by an enormous tsunami. It occurred to Walter Alvarez that if there had been a giant, impact-induced tsunami, it would have scoured away shorelines, leaving behind a distinctive fingerprint in the sedimentary record. He scanned the records of thousands of sediment cores that had been drilled in the oceans, and found such a fingerprint in cores from the Gulf of Mexico. Finally, a hundred-mile-wide crater was discovered or, more accurately, rediscovered, beneath the Yucatán Peninsula. Buried under half a mile of newer sediment, the crater had shown up in gravity surveys taken in the nineteen-fifties by Mexico’s state-run oil company. Company geologists had interpreted it as the traces of an underwater volcano and, since volcanoes don’t yield oil, promptly forgotten about it. When the Alvarezes went looking for cores the company had drilled in the area, they were told that they’d been destroyed in a fire; really, though, they had just been misplaced. The cores were finally located in 1991 and found to contain a layer of glass—rock that had melted “, then rapidly cooled—right at the K-T boundary. To the Alvarez camp, this was the clincher, and it was enough to move many uncommitted”scientists into the pro-impact column. “Crater supports extinction theory,” the Times announced. By this point, Luis Alvarez had died of complications from esophageal cancer. Walter dubbed the formation the “Crater of Doom.” It became more widely known, after the nearest town, as the Chicxulub crater.”

“Those eleven years seemed long at the time, but looking back they seem very brief,” Walter told me. “Just think about it for a moment. Here you have a challenge to a uniformitarian viewpoint that basically every geologist and paleontologist had been trained in, as had their professors and their professors’ professors, all the way back to Lyell. And what you saw was people looking at the evidence. And they gradually did come to change their minds.”

“WHEN the Alvarezes published their hypothesis, they knew of only three sites where the iridium layer was exposed: the two Walter had visited in Europe and a third, which they’d been sent samples from, in New Zealand. In the decades since, dozens more have been located, including one near a nude beach in Biarritz, another in the Tunisian desert, and a third in suburban New Jersey. Neil Landman, a paleontologist who specializes in ammonites, often takes field trips to this last site, and one warm fall day I invited myself to tag along. We met in front of the American Museum of Natural History, in Manhattan, where Landman has his office in a turret overlooking Central Park, and, together with a pair of graduate students, headed south to the Lincoln Tunnel.

Driving through northern New Jersey, we passed a succession of strip malls and car dealerships that seemed to repeat every few miles, like dominoes. Eventually, in the general vicinity of Princeton, we pulled into a parking lot next to a baseball field.

“(Landman would prefer that I not reveal the exact location of the field, for fear of attracting fossil collectors.) In the parking lot, we met up with a geologist named Matt Garb, who teaches at Brooklyn College. Garb, Landman, and the graduate students shouldered their gear. We circumnavigated the baseball field—empty in the middle of a school day—and struck out through the underbrush. Soon we reached a shallow creek. Its banks were covered in rust-colored slime. Brambles hung over the water. Fluttering from these were tattered banners of debris: lost plastic bags, scraps of newspaper, the rings from ancient six-packs. “To me, this is better than Gubbio,” Landman announced.”

“During the late Cretaceous, he explained to me, the park, the creek bed, and everything around us for many miles would have been under water. At that point, the world was very warm—lush forests grew in the Arctic—and sea levels were high. Most of New Jersey formed part of the continental shelf of what’s now eastern North America, which, as the Atlantic was then much narrower, was considerably closer to what’s now Europe. Landman pointed to a spot in the creek bed a few inches above the water line. There, he told me, was the iridium layer. Although it wasn’t in any way visibly different, Landman knew where it was because he’d had the sequence analyzed a few years earlier. Landman is stocky, with a wide face and a graying beard. He had dressed for the trip in khaki shorts and old sneakers. “He waded into the creek to join the others, who were already hacking at the bed with their pickaxes. Soon, someone found a fossilized shark’s tooth. Someone else dug out a piece of an ammonite. It was about the size of a strawberry and covered in little pimples, or tubercles. Landman identified it as belonging to the species Discoscaphites iris.”

“AMMONITES floated through the world’s shallow oceans for more than three hundred million years, and their fossilized shells turn up all around the world. Pliny the Elder, who died in the eruption that buried Pompeii, was already familiar with them, although he considered them to be precious stones. (The stones, he related in his Natural History, were said to bring prophetic dreams.) In medieval England, ammonites were known as “serpent stones,” and in Germany they were used to treat sick cows. In India, they were—and to a certain extent still are—revered as manifestations of Vishnu.”

“Like nautiluses, to whom they were distantly related, ammonites constructed spiral shells divided into multiple chambers. The animals themselves occupied only the last and largest chamber; the rest were filled with air, an arrangement that might be compared to an apartment building in which just the penthouse is rented. The walls between the chambers, known as septa, were fantastically elaborate, folded into intricate ruffles, “like the edges of a snowflake. (Individual species can be identified by the distinctive patterns of their pleats.) This evolutionary development allowed ammonites to build shells that were at once light and robust—capable of withstanding many atmospheres’ worth of water pressure. Most ammonites could fit in a human hand; some grew to be the size of kiddie pools.”

“Based on the number of teeth ammonites had—nine—it’s believed that their closest living kin are octopuses. But since ammonites’ soft body parts are virtually never preserved, what exactly the animals looked like and how they lived are largely matters of inference. It’s probable, though not certain, that they propelled themselves by shooting out a jet of water, which means that they could only travel backward.

“I remember when I was a kid taking paleontology, and I learned that pterodactyls could fly,” Landman told me. “My immediate question was, well, how high could they fly? And it’s hard to come up with those numbers.”

“I’ve studied ammonites for forty years, and I’m still not sure exactly what they liked,” he went on. “I feel they liked water twenty, thirty, maybe forty meters deep. They were swimmers “but not very good swimmers. I think they lived a quiet existence.” In drawings, ammonites are usually depicted as resembling squids that have been stuffed into snail shells. Landman, however, has trouble with this depiction. He believes that ammonites, though commonly shown with several streaming tentacles, in fact had none. In a drawing that accompanies a recent journal article he published in the journal Geobios, ammonites are shown looking like little more than blobs. They have stubby armlike appendages, which are arrayed in a circle and connected by a web of tissue. In males, one of the arms pokes up out of the webbing to form the cephalopod version of a penis.”

“Landman attended graduate school at Yale in the nineteen-seventies. As a student in the pre-Alvarez days, he was taught that ammonites were declining throughout the Cretaceous, so their eventual disappearance was nothing to get too worked up about. “The sense was, oh, you know, the ammonites were just dying out,” he recalled. Subsequent discoveries, many of them made by Landman himself, have shown that, on the contrary, ammonites were doing just fine.”

“Here you have lots of species, and we’ve collected thousands of specimens over the last few years,” he told me over the clank of the others’ pickaxes. Indeed, in the creek bed, Landman recently came upon two entirely new species of ammonite. One of these he named, in honor of a colleague, Discoscaphites minardi. The other he named, in honor of the place, Discoscaphites jerseyensis. Discoscaphites jerseyensis probably had little spines poking out of its shell, which, Landman speculates, helped the animal appear larger and more intimidating than it actually was.”

“IN their original paper, the Alvarezes proposed that the main cause of the K-T mass extinction was not the impact itself or even the immediate aftermath. The truly catastrophic effect of the asteroid—or, to use the more generic term, bolide—was the dust. In the intervening decades, this account has been subjected to numerous refinements. (The date of the impact has also been pushed back—to sixty-six million years ago.) Though scientists still vigorously argue about many of the details, one version of the event runs as follows:”

“The bolide arrived from the southeast, traveling at a low angle relative to the earth, so that it came in not so much from above as from the side, like a plane losing altitude. When it slammed into the Yucatán Peninsula, it was moving at something like forty-five thousand miles per hour, and, due to its trajectory, North America was particularly hard-hit. A vast cloud of searing vapor and debris raced over the continent, expanding as it moved and incinerating anything in its path. “Basically, if you were a triceratops in Alberta, you had about two minutes before you got vaporized” is how one geologist put it to me.”

“n the process of excavating the enormous crater, the asteroid blasted into the air more than fifty times its own mass in pulverized rock. As the ejecta fell back through the atmosphere, the particles incandesced, lighting the sky everywhere at once from directly overhead and generating enough heat to, in effect, broil the surface of the planet. Owing to the composition of the Yucatán Peninsula, the dust thrown up was rich in sulfur. Sulfate aerosols are particularly effective at blocking sunlight, which is the reason a single volcanic eruption, like Krakatoa, can depress global temperatures for years. After the initial heat pulse, the world experienced a multiseason “impact winter. “Forests were decimated. Palynologists, who study ancient spores and pollen, have found that diverse plant communities were replaced entirely by rapidly dispersing ferns. (This phenomenon has become known as the “fern spike.”) Marine ecosystems effectively collapsed, and they remained in that state for at least half a million, and perhaps as many as several million, years. (The desolate post-impact sea has been dubbed the “Strangelove ocean.”)

It’s impossible to give anything close to a full account of the various species, genera, families, and even whole orders that went extinct at the K-T boundary. On land, every animal larger than a cat seems to have died out. The event’s most famous victims, the dinosaurs—or, to be more precise, the non-avian dinosaurs—suffered a hundred percent losses. “Among the groups that were probably alive right up to the end of the Cretaceous were such familiar museum shop fixtures as hadrosaurs, ankylosaurs, tyrannosauruses, and triceratops. (The cover of Walter Alvarez’s book on the extinction, T. Rex and the Crater of Doom, shows an angry-looking tyrannosaurus reacting with horror to the impact.) Pterosaurs, too, disappeared. Birds were also hard-hit; perhaps three-quarters of all bird families, perhaps more, went extinct. Enantiornithine birds, which retained such archaic features as teeth, were wiped out, as were Hesperornithine birds, which were aquatic and for the most part flightless. “The same goes for lizards and snakes; around four-fifths of all species vanished. Mammals’ ranks, too, were devastated; something like two-thirds of the mammalian families living at the end of the Cretaceous disappear at the boundary.”

“In the sea, plesiosaurs, which Cuvier had at first found implausible and then “monstrous,” died out. So did mosasaurs, belemnites, and, of course, ammonites. Bivalves, familiar to us today in the form of mussels and oysters, suffered heavy casualties, as did brachiopods, which look like clams but have a totally different anatomy, and bryozoans, which look like corals but once again are totally unrelated. Several groups of marine microorganisms came within a micron or two of annihilation. Among planktonic foraminifera, something like ninety-five percent of all species disappeared, including Abathomphalus mayaroensis, whose remains are found in the last layer of Cretaceous limestone in Gubbio. (Planktonic foraminifera live near the ocean surface; benthic species live on the ocean floor.)

In general, the more that’s been learned about the K-T boundary, the more wrongheaded Lyell’s reading of the fossil record appears. The problem with the record is not that slow extinctions appear abrupt. It’s that even abrupt extinctions are likely to look protracted.”

“Consider the accompanying diagram. Every species has what is known as a “preservation potential”—the odds that an individual of that species will become fossilized—and this varies depending on, among other things, how common the animal is, where it lives, and what it’s made out of. (Thick-shelled marine organisms have a much better chance of being preserved than, say, birds with hollow bones.)”

“In this diagram, the large white circles represent species that are rarely fossilized, the medium-sized circles those that are preserved more frequently, and the small white dots species that are more abundant still. Even if all of these species died out at exactly the same moment, it would appear that the white-circle species had vanished much earlier, simply because its remains are rarer. This effect—known as the Signor-Lipps effect, after the scientists who first identified it—tends to “smear out” sudden extinction events, making them look like long, drawn-out affairs.”

“Following the K-T extinction, it took millions of years for life to recover its former level of diversity. In the meantime, many surviving taxa seem to have shrunk. This phenomenon, which can be seen in the very tiny forams that show up above the iridium layer at Gubbio, is called the Lilliput effect.”

“LANDMAN, Garb, and the graduate students chipped away at the creek bed all morning. Although we were in the middle of the country’s most densely populated state, not a single person passed by to wonder at what we were doing. As the day grew warmer and more humid, it was pleasant to stand ankle-deep in the water (though I did wonder about the reddish slime). Someone had brought along an empty cardboard box, and, since I didn’t have a pickax, I helped out by gathering up the fossils the others had found and arranging them in the box. “Several more bits of Discoscaphites iris turned up, as well as pieces of an ammonite, Eubaculites carinatus, which, instead of having a spiral shell, had one that was long and slender and shaped like a spear. (One theory of the ammonites’ demise, popular in the early part of the twentieth century, was that the uncoiled shells of species like Eubaculites carinatus indicated that the group had exhausted its practical possibilities and entered some sort of decadent, Lady Gaga-ish phase.) At one point, Garb rushed over in a flurry of excitement. He was carrying a fist-sized chunk of the creek “bed and pointed out to me, along one edge, what looked like a tiny fingernail. This, he explained, was a piece of an ammonite’s jaw. Ammonite jaws are more common than other body parts but still extremely rare.”

“It was worth the trip just for that,” he exclaimed.

It’s unclear what aspect of the impact—the heat, the darkness, the cold, the change in water chemistry—did in the ammonites. Nor is it entirely clear why some of their cephalopod cousins survived. In contrast to ammonites, nautiluses, for example, sailed through the extinction event: pretty much all of the species known from the end of the Cretaceous survived into the Tertiary.”

“One theory of the disparity starts with eggs. Ammonites produced very tiny eggs, only a few hundredths of an inch across. The resulting hatchlings, or ammonitellae, had no means of locomotion; they just floated near the surface of the water, drifting along with the current. Nautiluses, for their part, lay very large eggs, among the largest of all invertebrates, nearly an inch in diameter. Hatchling nautiluses emerge, after nearly a year’s gestation, as miniature adults and then immediately start swimming around, searching for food in the depths. Perhaps in the aftermath of the impact, conditions at the ocean surface were so toxic that ammonitellae could not survive, while lower down in the water column the situation was less dire, so juvenile nautiluses managed to endure.”

“Whatever the explanation, the contrasting fate of the two groups raises a key point. Everything (and everyone) alive today is descended from an organism that somehow survived the impact. But it does not follow from this that they (or we) are any better adapted. In times of extreme stress, the whole concept of fitness, at least in a Darwinian sense, loses its meaning: how could a creature be adapted, either well or ill, for conditions it has never before encountered in its entire evolutionary history? At such moments, what Paul Taylor, a paleontologist at London’s Natural History Museum, calls “the rules of the survival game” abruptly change. Traits that for many millions of years were advantageous all of a sudden become lethal (though it may be difficult, millions of years after the fact, to identify just what those traits were). And what holds for ammonites and nautiluses applies equally well to belemnites and squids, plesiosaurs and turtles, dinosaurs and mammals. The reason this book is being written by a hairy biped, rather than a scaly one, has more to do with dinosaurian misfortune than with any particular mammalian virtue.”

“There’s nothing ammonites were doing wrong,” Landman told me as we packed up the last fossils from the creek and prepared to head back to New York. “Their hatchlings would have been like plankton, which for all of their existence would have been terrific. What better way to get around and distribute the species? Yet here, in the end, it may well have been their undoing.”



Dicranograptus ziczac

“In 1949, a pair of Harvard psychologists recruited two dozen undergraduates for an experiment about perception. The experiment was simple: students were shown playing cards and asked to identify them as they flipped by. Most of the cards were perfectly ordinary, but a few had been doctored, so that the deck contained, among other oddities, a red six of spades and a black four of hearts. When the cards went by rapidly, the students tended to overlook the incongruities; they would, for example, assert that the red six of spades was a six of hearts, or call the black four of hearts a four of spades. When the cards went by more slowly, they struggled to make sense of what they were more slowly, they struggled to make sense of what they were seeing. Confronted with a red spade, some said it looked “purple” or “brown” or “rusty black.” Others were completely flummoxed.”

“The symbols “look reversed or something,” one observed.

“I can’t make the suit out, whatever it is,” another exclaimed. “I don’t know what color it is now or whether it’s a spade or heart. I’m not even sure now what a spade looks like! My God!”

The psychologists wrote up their findings in a paper titled “On the Perception of Incongruity: A Paradigm.” Among those who found this paper intriguing was Thomas Kuhn. To Kuhn, the twentieth century’s most influential historian of science, the experiment was indeed paradigmatic: it revealed how people process disruptive information. Their first impulse is to force it into a familiar framework: hearts, spades, clubs. Signs of mismatch are disregarded for as long as possible—the red spade looks “brown” or “rusty.” At the point the anomaly becomes simply too glaring, a crisis ensues—what the psychologists dubbed the “’My God!’ reaction.”

“This pattern was, Kuhn argued in his seminal work, The Structure of Scientific Revolutions, so basic that it shaped not only individual perceptions but entire fields of inquiry. Data that did not fit the commonly accepted assumptions of a discipline would either be discounted or explained away for as long as possible. The more contradictions accumulated, the more convoluted the rationalizations became. “In science, as in the playing card experiment, novelty emerges only with difficulty,” Kuhn wrote. But then, finally, someone came along who was willing to call a red spade a red spade. Crisis led to insight, and the old framework gave way to a new one. This is how great scientific discoveries or, to use the term Kuhn made so popular, “paradigm shifts” took place.”

“The history of the science of extinction can be told as a series of paradigm shifts. Until the end of the eighteenth century, the very category of extinction didn’t exist. The more strange bones were unearthed—mammoths, Megatherium, mosasaurs—the harder naturalists had to squint to fit them into a familiar framework. And squint they did. The giant bones belonged to elephants that had been washed north, or hippos that had wandered west, or whales with malevolent grins. When Cuvier arrived in Paris, he saw that the mastodon’s molars could not be fit into the established framework, a “My God” moment that led him to propose a whole new way of seeing them. Life, Cuvier recognized, had a history. This history was marked by loss and punctuated by events too terrible for human imagining. “Though the world does not change with a change of paradigm, the scientist afterward works in a different world” is how Kuhn put it.”

“In his Recherches sur les ossemens fossiles, Cuvier listed dozens of espèces perdues, and he felt sure there were more awaiting discovery. Within a few decades, so many extinct creatures had been identified that Cuvier’s framework began to crack. To keep pace with the growing fossil record, the number of disasters had to keep multiplying. “God knows how many catastrophes” would be needed, Lyell scoffed, poking fun at the whole endeavor. Lyell’s solution was to reject catastrophe altogether. In Lyell’s—and later Darwin’s—formulation, extinction was a lonely affair. Each species that had vanished had shuffled off all on its own, a victim of the “struggle for life” and its own defects as a “less improved form.”

“The uniformitarian account of extinction held up for more than a century. Then, with the discovery of the iridium layer, science faced another crisis. (According to one historian, the Alvarezes’ work was “as explosive for science as an impact would have been for earth.”) The impact hypothesis dealt with a single moment in time—a terrible, horrible, no-good day at the end of the Cretaceous. But that single moment was enough to crack the framework of Lyell and Darwin. Catastrophes did happen.”

“What is sometimes labeled neocatastrophism, but is mostly nowadays just regarded as standard geology, holds that conditions on earth change only very slowly, except when they don’t. In this sense the reigning paradigm is neither Cuvierian nor Darwinian but combines key elements of both—“long periods of boredom interrupted occasionally by panic.” Though rare, these moments of panic are disproportionately important. They determine the pattern of extinction, which is to say, the pattern of life.”

“THE path leads up a hill, across a fast-moving stream, back across the stream, and past the carcass of a sheep, which, more than just dead, looks deflated, like a lost balloon. The hill is bright green but treeless; generations of the sheep’s aunts and uncles have kept anything from growing much above muzzle-height. In my view, it’s raining. Here in the Southern Uplands of Scotland, though, I’m told by one of the geologists I’m hiking with, this counts only as a light drizzle, or smirr.”

“Our goal is 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 reach the cliff, the smirr seems to be smirring harder. There’s a view over a waterfall, which crashes down into a narrow valley. A few yards farther up the path there’s a jagged outcropping of rock, which is striped vertically, like an umpire’s jersey, in bands of light and dark. Jan Zalasiewicz, a stratigrapher from the University of Leicester, sets his rucksack down on the soggy ground and adjusts his red rain jacket. He points to one of the light-colored stripes. “Bad things happened in here,” he tells me.”

“The rocks that we are looking at date back some 445 million years, to the last part of the Ordovician period. At that point, the globe was experiencing a continental logjam; most of the land—including what’s now Africa, South America, Australia, and Antarctica—was joined into one giant mass, Gondwana, which spanned more than ninety degrees latitude. England belonged to the continent—now lost—of Avalonia, and Dob’s Linn lay in the Southern Hemisphere, at the bottom of an ocean known as the Iapetus.”

“The Ordovician period followed directly after the Cambrian, which is known, even to the most casual of geology students, for the “explosion” of new life forms that appeared.* The Ordovician, too, was a time when life took off excitedly in new directions—the so-called Ordovician radiation—though it remained, for the most part, still confined to the water. During the Ordovician, the number of marine families tripled, and the seas filled with creatures we would more or less recognize (the progenitors of today’s starfish and sea urchins and snails and nautiluses) and also plenty that we would not (conodonts, which probably were shaped like eels; trilobites, which sort of resembled horseshoe crabs; and giant sea scorpions, which, as best as can be determined, looked like something out of a nightmare).”

“The first reefs appeared, and the ancestors of today’s clams took on their clam-like form. Toward the middle of the Ordovician, the first plants began to colonize the land. These were very early mosses or liverworts, and they clung low to the ground, as if not quite sure what to make of their new surroundings.”

“At the end of the Ordovician, some 444 million years ago, the oceans emptied out. Something like eighty-five percent of marine species died off. For a long time, the event was regarded as one of those pseudo-catastrophes that just went to show how little the fossil record could be trusted. Today, it’s seen as the first of the Big Five extinctions, and it’s thought to have taken place in two brief, intensely deadly pulses. Though its victims are nowhere near as charismatic as those taken out at the end of “the Cretaceous, it, too, marks a turning point in life’s history—a moment when the rules of the game suddenly flipped, with consequences that, for all intents and purposes, will last forever.”

“Those animals and plants that made it through the Ordovician extinction “went on to make the modern world,” the British paleontologist Richard Fortey has observed. “Had the list of survivors been one jot different, then so would the world today.”

“ZALASIEWICZ—MY guide at Dob’s Linn—is a slight man with shaggy hair, pale blue eyes, and a pleasantly formal manner. He is an expert on graptolites, a once vast and extremely diverse class of marine organisms that thrived during the Ordovician and then, in the extinction event, were very nearly wiped out. To the naked eye, graptolite fossils look like scratches or in some cases tiny petroglyphs. (The word “graptolite” comes from the Greek meaning “written rock”; it 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 individual, known as a zooid, built itself a tiny, tubular shelter, known as a theca, which 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. No one knows exactly what the zooids looked like—as with ammonites, the creatures’ soft parts resist preservation—but graptolites are now believed to be related to pterobranchs, a small and hard-to-find class of living marine organisms that resemble Venus flytraps.”

“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 compares them to Natasha, “the tender heroine of War and Peace. They were, he says, “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.”

“Finding graptolites at Dob’s Linn turns out, even for the most amateur of collectors, to be easy. The dark stone in the jagged outcropping is shale. It takes only a gentle hammer-tap to dislodge a chunk. Another tap splits the chunk laterally. It divides like a book opening to a well-thumbed page. Often on the stony surface there’s nothing to see, but just as often there’s one (or more) faint marks—messages from a former world. One of the graptolites I happen across has been preserved with peculiar clarity. It’s shaped like a set of false eyelashes, but very small, as if for a Barbie. Zalasiewicz tells me—doubtless exaggerating—that I have found a “museum quality specimen.” I pocket it.”

“Once Zalasiewicz shows me what to look for, I, too, can make out the arc of the extinction. In the dark shales, graptolites are plentiful and varied. Soon I’ve collected so many, the pockets of my jacket are sagging. Many of the fossils are variations on the letter V, with two arms branching away from a central node. Some look like zippers, others like wishbones. Still others have arms growing off their arms like tiny trees.”

“The lighter stone, by contrast, is barren. There’s barely a graptolite to be found in it. The transition from one state to another—from black stone to gray, from many graptolites to almost none—appears to have occurred suddenly and, according to Zalasiewicz, did occur suddenly.”

“The change here from black to gray marks a tipping point, if you like, from a habitable sea floor to an uninhabitable one,” he tells me. “And one might have seen that in the span of a human lifetime.” He describes this transition as distinctly “Cuvierian.”

“Two of Zalasiewicz’s colleagues, Dan Condon and Ian Millar, of the British Geological Survey, have made the hike with us out to Dob’s Linn. The pair are experts in isotope chemistry and are planning to collect samples from each of the stripes in the outcropping—samples they hope will contain tiny crystals of zircon. Once back at the lab, they will dissolve the crystals and run the results through a mass spectrometer. This will allow them to say, give or take half a million years or so, when each of the layers was formed. Millar is Scottish and claims to be undaunted by the smirr. “Eventually, though, even he has to acknowledge that, in English, it’s pouring. Rivulets of mud are running down the face of the outcropping, making it impossible to get clean samples. It is decided that we will try again the following day. The three geologists pack up their gear, and we squish back down the trail to the car. Zalasiewicz has made reservations at a bed-and-breakfast in the nearby town of Moffat, whose attractions, I have read, include the world’s narrowest hotel and a bronze sheep.”

“Once everyone has changed into dry clothes, we meet in the sitting room of the B & B for tea. Zalasiewicz has brought along several recent publications of his on graptolites. Settling back in their chairs, Condon and Millar roll their eyes. Zalasiewicz ignores them, patiently explaining to me the import of his latest monograph, “Graptolites in British Stratigraphy,” which runs sixty-six single-spaced pages and includes detailed illustrations of more than 650 species. In the monograph, the effects of the extinction show up more systematically, if also less vividly than on the rain-slicked hillside. Until the end of the Ordovician, V-shaped graptolites dominated. “ These included species like Dicranograptus ziczac, whose tiny cups were arranged along arms that curled away and then toward each other, like tusks, and Adelograptus divergens, which, in addition to its two main arms, had little side-arms that stuck out like thumbs. “Only a handful of graptolite species survived the extinction event; eventually, these diversified and repopulated the seas in the Silurian. But Silurian graptolites had a streamlined body plan, more like a stick than a set of branches. The V-shape had been lost, never to reappear. Here writ very, very small is the fate of the dinosaurs, the mosasaurs, and the ammonites—a once highly successful form relegated to oblivion.”

“WHAT happened 444 million years ago to nearly wipe out the graptolites, not to mention the conodonts, the brachiopods, the echinoderms, and the trilobites?”

“In the years immediately following the publication of the Alvarez hypothesis, it was generally believed—at least among those who considered the hypothesis more than “codswallop”—that a unified theory of mass extinction was at hand. If an asteroid had produced one “chasm” in the fossil record, it seemed reasonable to expect that impacts had caused all of them. This idea received a boost in 1984, when a pair of paleontologists from the University of Chicago published a comprehensive analysis of the marine fossil record.”

“The study revealed that in addition to the five major mass extinctions, there had been “many lesser extinction events. When all of these were considered together, a pattern emerged: mass extinctions seemed to take place at regular intervals of roughly twenty-six million years. Extinction, in other words, occurred in periodic bursts, like cicadas crawling out of the earth. The two paleontologists, David Raup and Jack Sepkoski, were unsure what had caused these bursts, but their best guess was some “astronomical and astrophysical cycle,” having to do with “the passage of our solar system through the spiral arms of the Milky Way. A group of astrophysicists—as it happened, colleagues of the Alvarezes at Berkeley—took the speculation one step farther. The periodicity, the group argued, could be explained by a small “companion star” to the sun, which, every twenty-six million years, passed through the Oort cloud, producing comet showers that rained destruction on the earth. The fact that no one had ever seen this star, dubbed with horror-movie flair “Nemesis,” was, to the Berkeley group, a problem, but not an insurmountable one; there were plenty of small stars out there, still waiting to be cataloged.”

“In the popular media, what became known as the “Nemesis Affair” generated almost as much excitement as the original asteroid hypothesis. (One reporter described the story as having everything but sex and the royal family.) Time ran a cover article, which was soon followed by another disapproving editorial in the New York Times. (The editorial pooh-poohed the notion of a “mysterious death-star.”) This time, the newspaper was onto something. Though the Berkeley group spent the next year or so scanning the heavens for Nemesis, no glimmer of a “death star” was discovered. More significantly, upon further analysis, the evidence for periodicity began to fall apart. “If there’s a consensus, it’s that what we were seeing was a statistical fluke,” David Raup told me.”

“Meanwhile, the search for iridium and other signs of extraterrestrial impacts was faltering. Together with many others, Luis Alvarez had thrown himself into this hunt. At a time when scientific collaboration with the Chinese was practically unheard of, he’d managed to obtain rock samples from southern China that spanned the boundary between the Permian and Triassic periods. The end-Permian or Permo-Triassic extinction was the biggest of the Big Five, an episode that came scarily close to eliminating multicellular life altogether. Luis was thrilled to find a layer of clay nestled between the bands of rock from southern China, just as there had been at Gubbio. “We felt sure that there would be lots of iridium there,” he would later recall. But the Chinese clay turned out to be, chemically speaking, mundane, its iridium content too infinitesimal to be measured. Higher-than-normal iridium levels were subsequently detected at the end of the Ordovician, in rocks from, among other places, Dob’s Linn. ”

“However, none of the other telltale signs of an impact, such as shocked quartz, turned up in the right time frame, and “it was determined that the elevated iridium levels were more plausibly—if less spectacularly—attributed to the vagaries of sedimentation”

“The current theory is that the end-Ordovician extinction was caused by glaciation. For most of the period, a so-called greenhouse climate prevailed—carbon dioxide levels in the air were high and so, too, were sea levels and temperatures. But right around the time of the first pulse of extinction—the one that wreaked havoc among the graptolites—CO2 levels dropped. Temperatures fell and Gondwana froze. Evidence of the Ordovician glaciation has been found in such far-flung remnants of the supercontinent as Saudi Arabia, Jordan, and Brazil. Sea levels plummeted, and many marine habitats were eliminated, presumably to the detriment of marine organisms. The oceans’ chemistry changed, too; among other things, colder water holds more oxygen. “No one is sure whether it was the temperature change or one of the many knock-on effects that killed the graptolites; as Zalasiewicz put it to me, “You have a body in the library, and a half a dozen butlers wandering around, looking sheepish.” Nor does anyone know what caused the change to begin with. One theory has it that the glaciation was produced by the early mosses that colonized the land and, in so doing, helped draw carbon dioxide out of the air. If this is the case, the first mass extinction of animals was caused by plants.”

“The end-Permian extinction also seems to have been triggered by a change in the climate. But in this case, the change went in the opposite direction. Right at the time of extinction, 252 million years ago, there was a massive release of carbon into the air—so massive that geologists have a hard time even imagining where all the carbon could have come from. Temperatures soared—the seas warmed by as much as eighteen degrees—and the chemistry of the oceans went haywire, as if in an out-of-control aquarium. The water became acidified, and the amount of dissolved oxygen dropped so low that many organisms probably, in effect, suffocated. Reefs collapsed. “The end-Permian extinction took place, though not quite in a human lifetime, in geologic terms nearly as abruptly; according to the latest research by Chinese and American scientists, the whole episode lasted no more than two hundred thousand years, and perhaps less than a hundred thousand. By the time it was over, something like ninety percent of all species on earth had been eliminated. Even intense global warming and ocean acidification seem inadequate to explain losses on such a staggering scale, and so additional mechanisms are still being sought. One hypothesis has it that the heating of the oceans favored bacteria that produce hydrogen sulfide, which is poisonous to most other forms of life. According to this scenario, hydrogen sulfide accumulated in the water, killing off marine creatures, then it leaked into the air, killing off most everything else. The sulfate- “reducing bacteria changed the color of the oceans and the hydrogen sulfide the color of the heavens; the science writer Carl Zimmer has described the end-Permian world as a “truly grotesque place” where glassy, purple seas released poisonous bubbles that rose “to a pale green sky.”

“If twenty-five years ago it seemed that all mass extinctions would ultimately be traced to the same cause, now the reverse seems true. As in Tolstoy, every extinction event appears to be unhappy—and fatally so—in its own way. It may, in fact, be the very freakishness of the events that renders them so deadly; all of a sudden, organisms find themselves facing conditions for which they are, evolutionarily, completely unprepared.”

“I think that, after the evidence became pretty strong for the impact at the end of the Cretaceous, those of us who were working on this naively expected that we would go out and find evidence of impacts coinciding with the other events,” Walter Alvarez told me. “And it’s turned out to be much more complicated. We’re seeing right now that a mass extinction can be caused by human beings. So it’s clear that we do not have a general theory of mass extinction.”

“THAT evening in Moffat, once everyone had had enough of tea and graptolites, we went out to the pub on the ground floor of the world’s narrowest hotel. After a pint or two, the conversation turned to another one of Zalasiewicz’s favorite subjects: giant rats. Rats have followed humans to just about every corner of the globe, and it is Zalasiewicz’s professional opinion that one day they will take over the earth.”

“Some number will probably stay rat-sized and rat-shaped,” he told me. “But others may well shrink or expand. Particularly if there’s been epidemic extinction and ecospace opens up, rats may be best placed to take advantage of that. And we know that change in size can take place fairly quickly.” I recalled a rat I once watched drag a pizza crust along the tracks at an Upper West Side subway station. I imagined it waddling through a deserted tunnel blown up to the size of a Doberman.”

“Though the connection might seem tenuous, Zalasiewicz’s interest in giant rats represents a logical extension of his interest in graptolites. He is fascinated by the world that preceded humans and also—increasingly—by the world that humans will leave behind. One project informs the other. When he studies the Ordovician, he’s trying to reconstruct the distant past on the basis of the fragmentary clues that remain: fossils, isotopes of carbon, layers of sedimentary rock. When he contemplates the future, he’s trying to imagine what will remain of the present once the contemporary world has been reduced to fragments: fossils, isotopes of carbon, layers of sedimentary rock. “Zalasiewicz is convinced that even a moderately competent stratigrapher will, at the distance of a hundred million years or “so, be able to tell that something extraordinary happened at the moment in time that counts for us as today. This is the case even though a hundred million years from now, all that we consider to be the great works of man—the sculptures and the libraries, the monuments and the museums, the cities and the factories—will be compressed into a layer of sediment not much thicker than a cigarette paper. “We have already left a record that is now indelible,” Zalasiewicz has written.”

“One of the ways we’ve accomplished this is through our restlessness. Often purposefully and just as often not, humans have rearranged the earth’s biota, transporting the flora and fauna of Asia to the Americas and of the Americas to Europe and of Europe to Australia. Rats have consistently been on the vanguard of these movements, and they have left their bones scattered everywhere, including on islands so remote that humans never bothered to settle them. The Pacific rat, Rattus exulans, a native of southeast Asia, traveled with Polynesian seafarers to, among many other places, Hawaii, Fiji, Tahiti, Tonga, Samoa, Easter Island, and New Zealand. Encountering few predators, stowaway Rattus exulans multiplied into what the New Zealand paleontologist Richard Holdaway has described as “a grey tide” that turned “everything edible into rat protein.” (A recent study of pollen and animal remains on Easter Island concluded that it wasn’t humans who deforested the landscape; rather, it was the rats that came along for the ride and then bred unchecked. ”

“The native palms couldn’t produce seeds fast enough to keep up with their appetites.) When Europeans arrived in the Americas, and then continued west to the islands the Polynesians had settled, they brought with them the even-more-adaptable Norway rat, Rattus norvegicus.” “In many places, Norway rats, which are actually from China, outcompeted the earlier rat invaders and, in so doing, ravaged the bird and reptile populations the Pacific rats had missed. Rats thus might be said to have created their own “ecospace,” which their progeny seem well positioned to dominate. The descendants of today’s rats, according to Zalasiewicz, will radiate out to fill the niches that Rattus exulans and Rattus norvegicus helped empty. He imagines the rats of the future evolving into new shapes and sizes—some “smaller than shrews,” others as large as elephants. “We might,” he has written, “include among them—for curiosity’s sake and to keep our options open—a species or two of large naked rodent, living in caves, shaping rocks as primitive tools and wearing the skins of other mammals that they have killed and eaten.”

“Meanwhile, whatever the future holds for rats, the extinction event that they are helping to bring about will leave its own distinctive mark. Not yet anywhere near as drastic as the one recorded in the mudstone at Dob’s Linn or in the clay layer in Gubbio, it will nevertheless appear in the rocks as a turning point. Climate change—itself a driver of extinction—will also “leave behind geologic traces, as will nuclear fallout and river diversion and monoculture farming and ocean acidification.”

“For all of these reasons, Zalasiewicz believes that we have entered a new epoch, which has no analog in earth’s history. “Geologically,” he has observed, “this is a remarkable episode.”

“OVER the years, a number of different names have been suggested for the new age that humans have ushered in. The noted conservation biologist Michael Soulé has suggested that instead of the Cenozoic, we now live in the “Catastrophozoic” era. Michael Samways, an entomologist at South Africa’s Stellenbosch University, has floated the term “Homogenocene.” Daniel Pauly, a Canadian marine biologist, has proposed the “Myxocene,” from the Greek word for “slime,” and Andrew Revkin, an American journalist, has offered the “Anthrocene.” (Most of these terms owe their origins, indirectly at least, to Lyell, who, back in the eighteen-thirties, coined the words Eocene, Miocene, and Pliocene.)”

“The word “Anthropocene” is the invention of Paul Crutzen, a Dutch chemist who shared a Nobel Prize for discovering the effects of ozone-depleting compounds. The importance of this discovery is difficult to overstate; had it not been made—and had the chemicals continued to be widely used—the ozone “hole” that opens up every spring over Antarctica would have expanded until eventually it encircled the entire earth. (One of Crutzen’s fellow Nobelists reportedly came home from his lab one night and told his wife, “The work is going well, but it looks like it might be the end of the world.”)”

“Crutzen told me that the word “Anthropocene” came to him while he was sitting at a meeting. The meeting’s chairman kept referring to the Holocene, the “wholly recent” epoch, which began at the conclusion of the last ice age, 11,700 years ago, and which continues—at least officially—to this day.”

“Let’s stop it,’” Crutzen recalled blurting out. “’We are no longer in the Holocene; we are in the Anthropocene.’ Well, it was quiet in the room for a while.” At the next coffee break, the Anthropocene was the main topic of conversation. Someone came up to Crutzen and suggested that he patent the term.

Crutzen wrote up his idea in a short essay, “Geology of Mankind,” that ran in Nature. “It seems appropriate to assign the term ‘Anthropocene’ to the present, in many ways human-dominated, geological epoch,” he observed. Among the many geologic-scale changes people have effected, Crutzen cited the following:

• Human activity has transformed between a third and a half of the land surface of the planet.

• Most of the world’s major rivers have been dammed or diverted.”

“• Fertilizer plants produce more nitrogen than is fixed naturally by all terrestrial ecosystems.

• Fisheries remove more than a third of the primary production of the oceans’ coastal waters.

• Humans use more than half of the world’s readily accessible fresh water runoff.”

“Most significantly, Crutzen said, people have altered the composition of the atmosphere. Owing to a combination of fossil fuel combustion and deforestation, the concentration of carbon dioxide in the air has risen by forty percent over the last two centuries, while the concentration of methane, an even more potent greenhouse gas, has more than doubled.

“Because of these anthropogenic emissions,” Crutzen wrote, the global climate is likely to “depart significantly from natural behavior for many millennia to come.”

Crutzen published “Geology of Mankind” in 2002. Soon, the “Anthropocene” began migrating out into other scientific journals.”

“Global Analysis of River Systems: From Earth System Controls to Anthropocene Syndromes” was the title of a 2003 article in the journal Philosophical Transactions of the Royal Society B.

“Soils and Sediments in the Anthropocene” ran the headline of a piece from 2004 in the Journal of Soils and Sediments.

When Zalasiewicz came across the term, he was intrigued. He noticed that most of those using it were not trained stratigraphers, and he wondered how his colleagues felt about this. At the time, he was head of the stratigraphy committee of the Geological Society of London, the body Lyell and also William Whewell and John Phillips once presided over. At a luncheon meeting, Zalasiewicz asked his fellow committee members what they thought of the Anthropocene. Twenty-one out of the twenty-two thought that the concept had merit.”

“The group decided to examine the idea as a formal problem in geology. Would the Anthropocene satisfy the criteria used for naming a new epoch? (To geologists, an epoch is a subdivision of a period, which, in turn, is a division of an era: the Holocene, for instance, is an epoch of the Quaternary, which is a period in the Cenozoic.) The answer the members arrived at after a year’s worth of study was an unqualified “yes.” The sorts of changes that Crutzen had enumerated would, they decided, leave behind “a global stratigraphic signature” that would still be legible millions of years from now, the same way that, say, the Ordovician glaciation left behind a “stratigraphic signature” that is still legible today. Among other things, the members of the group observed in a paper summarizing their findings, the Anthropocene will be marked by a unique “biostratigraphical signal,” a product of the current extinction event on the one hand and of the human propensity for redistributing life on the other. “signal will be permanently inscribed, they wrote, “as future evolution will take place from surviving (and frequently anthropogenically relocated) stocks.” Or, as Zalasiewicz would have it, rats.”

“By the time of my visit to Scotland, Zalasiewicz had taken the case for the Anthropocene to the next level. The International Commission on Stratigraphy, or ICS, is the group responsible for maintaining the official timetable of earth’s history. It’s the ICS that settles such matters as: when exactly did the Pleistocene begin? (After much heated debate, the commission recently moved that epoch’s start date back from 1.8 to 2.6 million years ago.) Zalasiewicz had convinced the ICS to look into formally recognizing the Anthropocene, an effort that, logically enough, he himself was put in charge of. As head of the Anthropocene Working Group, Zalasiewicz is hoping to bring a proposal to a vote by the full body in 2016. If he’s successful and the Anthropocene is adopted as a new epoch, every geology textbook in the world immediately will become obsolete.”

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