The Best American Science and Nature Writing 2014 (27 page)

Zalasiewicz's colleagues from the British Geological Survey, Dan Condon and Ian Millar, had come to Dob's Linn to collect samples from the various stripes. (Zalasiewicz also worked for many years at the BGS; he now teaches at the University of Leicester.) The samples, they hoped, would contain tiny crystals of zircon, which, after some complicated chemical manipulations, would allow them to date the layers of rock quite precisely. Millar, who grew up in Scotland, at first claimed to be undaunted by the smirr. But after a while even he admitted that it was pouring. Rivulets of mud were cascading down the face of the outcropping, compromising the samples. It was decided that we would have to come back the following day. The geologists packed up their gear and we squished back down the trail to the car. Zalasiewicz had made reservations at a bed-and-breakfast in the nearby town of Moffat. The town's attractions, I had read, included Britain's narrowest hotel and a bronze sheep.

 

The idea that the world can change suddenly and drastically—“in the span of a human lifetime”—is very old and, at the same time, very new. To the early members of the Geol Soc, the role of catastrophe in the earth's history was self-evident. These men—and they were, of course, all men—had read the great nineteenth-century French naturalist Georges Cuvier, who interpreted the fossil record as a chronicle of recurring tragedy. (When the Napoleonic Wars ended in 1815, Cuvier was made an honorary Geol Soc member.)

“Life on earth has often been disturbed by terrible events,” Cuvier wrote. “Living organisms without number have been the victims of these catastrophes.”

Cuvier's view of life was challenged by Charles Lyell, another of the nineteenth century's most influential naturalists. According to Lyell, who served as the Geol Soc's fourteenth president and also as its twenty-first, the earth was capable of changing only very gradually. The way to understand the distant past was to look at the present. Since no one had ever seen the kind of cataclysm that Cuvier invoked, it was unscientific or, to use Lyell's term, “unphilosophical,” to imagine that such events took place. If it appeared from the fossil record that the world had changed abruptly, Lyell maintained, this just went to show how little the record was to be trusted.

Among the early converts to Lyell's view was Charles Darwin. In
On the Origin of Species
, Darwin acknowledged that there were points in the earth's history when it appeared that “whole families or orders” had suddenly been exterminated. But like Lyell, he took this as evidence that “wide intervals of time” were unaccounted for. Had the evidence of these intervals not been lost, it would have shown “much slow extermination.” He wrote, “So profound is our ignorance, and so high our presumption, that we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world!”

Such was Lyell and Darwin's influence that for more than a century, even as it became increasingly clear that “whole families or orders” had indeed at various points suddenly been eliminated, geologists eschewed any account of these episodes that might be construed as Cuvierian. This reluctance extended into the 1980s, when it was proposed that an asteroid plowing into the earth at the end of the Cretaceous period, 65 million years ago, was what had done in the dinosaurs, along with the plesiosaurs, the mosasaurs, the pterosaurs, the ammonites, most birds, and a significant proportion of mammals. The impact hypothesis was resisted until the 1990s, when the existence of a huge impact crater formed precisely at the end of the Cretaceous was confirmed. The crater lies off the Yucatán Peninsula, buried under half a mile of newer sediment.

While the discovery of the impact crater didn't exactly invalidate Lyell and Darwin's model, it revealed their dismissal of catastrophe to have been itself “unphilosophical.” Life on earth
has
been “disturbed by terrible events,” and “living organisms without number” have been their victims. What is sometimes called “neocatastrophism,” but is mostly now just considered mainstream geology, holds that the world changes only very slowly, except when it doesn't.

As best as can be determined, the rate of change today is as fast as it's been at any time since the asteroid impact. This is why Zalasiewicz believes that the stratigraphers of the future should have a relatively easy time of it, even though who or what was responsible for the sudden alteration of the planet may not immediately be clear. At one point he mused, “It may take them a little while to sort out whether we were the drivers of this, or if the cats or the dogs or the sheep were.”

 

After everyone had changed into dry clothes, we met in the sitting room of the B & B for tea. Zalasiewicz had brought along several papers he had recently published on graptolites. Settling back in their chairs, Condon and Millar rolled their eyes. Zalasiewicz ignored them, patiently explaining to me the import of his latest monograph, “Graptolites in British Stratigraphy,” which ran to sixty-six pages and included illustrations of more than 650 species. In the monograph, the effects of the extinction event showed up more systematically, if also less vividly, than on the rain-slicked hillside. Until the end of the Ordovician, V-shaped graptolites were common. These included species like the
Dicranograptus ziczac
, whose tiny cups were arranged along arms that curled away and then toward each other, like tusks; and
Amphigraptus divergens
, which was shaped like a bat in flight. Only a handful of graptolite species survived the end-Ordovician extinction, which, it's now believed, was caused by the sudden glaciation of the supercontinent Gondwana. (No one is entirely sure what caused this glaciation.) Eventually the surviving graptolites diversified and repopulated the seas of 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, was the fate of the dinosaurs, the pterosaurs, and the ammonites—a once highly successful form now relegated to oblivion.

That evening, when everyone had had enough of tea and graptolites, we went out to the pub on the ground floor of Britain's narrowest hotel, which is twenty feet across. After a pint or two, the conversation turned to another one of Zalasiewicz's favorite subjects: giant rats. Zalasiewicz pointed out that rats have followed humans to just about every corner of the globe, and it is his professional opinion that one day they will take over the earth.

“Some number will probably stay rat-size 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 once watching a rat 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. When he studies the Ordovician and the Silurian, 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. One of the many aspects of the Anthropocene that he believes will leave a permanent mark is a reshuffling of the biosphere.

Often purposefully and just as often not, people have transported living things around the globe, importing the flora and fauna of Asia to the Americas and of the Americas to Europe and of Europe to Australia. Rats have consistently been in 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 Richard Holdaway, a New Zealand paleontologist, has described as “a grey tide” that turned “everything edible into rat protein.” (A recent study in the
Journal of Archaeological Science
concluded that it wasn't humans who deforested Easter Island; 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 appetite.)

When Europeans arrived in the Americas and then continued west to the islands that 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 ravaged whatever 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 in
The Earth After Us
(2008), “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 mark. Many evolutionary lineages have recently come to an end; many, many more are likely soon to follow. Extinction rates today are hundreds of times higher—for some groups, such as amphibians and freshwater mollusks, perhaps thousands, or even tens of thousands, of times higher—than they've been since mammals took over the ecospace emptied by the dinosaurs. For reasons of geological history, the current extinction event is often referred to as the “sixth extinction.” (By this accounting, the event recorded in the rocks at Dob's Linn is the first of the five major mass extinctions that have occurred since complex animal life evolved.) Whether the sixth extinction will turn out to be anywhere near as drastic as the first is impossible to know; nevertheless, it is likely to appear in the fossil record as a turning point. Climate change—itself a driver of extinction—will also leave behind geological traces, as will deforestation, industrial pollution, and monoculture farming.

Ultimately, most of our carbon emissions will end up in the oceans; this will dramatically alter the chemistry of the water, turning it more acidic. Ocean acidification is associated with some of the worst crises in biotic history, including what's known as the end-Permian extinction—the third of the so-called Big Five—which took place roughly 250 million years ago and killed off something like 90 percent of the species on the planet.

“Oh, ocean acidification,” Zalasiewicz said when we returned to Dob's Linn the following day. “That's the big nasty one that's coming down.”

 

In recent years, a number of names have been proposed 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 recommended 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 1830s, coined the names Eocene, Miocene, and Pliocene.)

The word “Anthropocene” was put into circulation by Paul Crutzen, a Dutch chemist who, in 1995, 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 globe. One of Crutzen's fellow Nobelists reportedly came home from his lab one night and said to his wife, “The work is going well, but it looks like the end of the world.”

Crutzen once told me that the word “Anthropocene” came to him while he was in 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, eleven and a half thousand years ago. According to the International Commission on Stratigraphy, or ICS, which maintains the official geological time scale, the Holocene continues 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, titled “Geology of Mankind,” which ran in the journal
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.

Many of the world's major rivers have been dammed or diverted.