The Best American Science and Nature Writing 2010

by Tim Folger

  To test his hypothesis, Speare began collecting samples from live African clawed frogs and also from specimens preserved in museums. He found that specimens dating back to the 1930s were indeed already carrying the fungus. He also found that live African clawed frogs were widely infected with Bd but seemed to suffer no ill effects from it. In 2004 he coauthored an influential paper that argued that the transmission route for the fungus began in southern Africa and ran through clinics and hospitals around the world.

  "Let's say people were raising African clawed frogs in aquariums, and they just popped the water out," Speare told me. "In most cases when they did that, no frogs got infected, but then, on that hundredth time, one local frog might have been infected. Or people might have said, 'I'm sick of this frog, I'm going to let it go.' And certainly there are populations of African clawed frogs established in a number of countries around the world, to illustrate that that actually did occur."

  At this point, Bd appears to be, for all intents and purposes, unstoppable. It can be killed by bleach—Clorox is among the donors to EVACC—but it is impossible to disinfect an entire rainforest. Sometime in the last year or so, the fungus jumped the Panama Canal. (When Edgardo Griffith swabbed the frogs on our trip, he was collecting samples that would eventually be analyzed for it.) It also seems to be heading into Panama from the opposite direction, out of Colombia. It has spread through the highlands of South America, down the eastern coast of Australia, and into New Zealand, and has been detected in Italy, Spain, and France. In the United States, it appears to have radiated from several points, not so much in a wavelike pattern as in a series of ripples.

  In the fossil record, mass extinctions stand out so sharply that the very language scientists use to describe Earth's history derives from them. In 1840 the British geologist John Phillips divided life into three chapters: the Paleozoic (from the Greek for "ancient life"), the Mesozoic ("middle life"), and the Cenozoic ("new life"). Phillips fixed as the dividing point between the first and second eras what would now be called the end-Permian extinction, and that between the second and third the end-Cretaceous event. The fossils from these eras were so different that Phillips thought they represented three distinct episodes of creation.

  Darwin's resistance to catastrophism meant that he couldn't accept what the fossils seemed to be saying. Drawing on the work of the eminent geologist Charles Lyell, a good friend of his, Darwin maintained that the apparent discontinuities in the history of life were really just gaps in the archive. In On the Origin of Species, he argued:

  With respect to the apparently sudden extermination of whole families or orders, as of Trilobites at the close of the palaeozoic period and of Ammonites at the close of the secondary period, we must remember what has been already said on the probable wide intervals of time between our consecutive formations; and in these intervals there may have been much slow extermination.

  All the way into the 1960s, paleontologists continued to give talks with titles like "The Incompleteness of the Fossil Record." And this view might have persisted even longer had it not been for a remarkable, largely inadvertent discovery made in the following decade.

  In the mid-1970s, Walter Alvarez, a geologist at the Lamont Doherty Earth Observatory, in New York, was studying Earth's polarity. It had recently been learned that the orientation of the planet's magnetic field reverses, so that every so often, in effect, south becomes north and vice versa. Alvarez and some colleagues had found that a certain formation of pinkish limestone in Italy, known as the scaglia rossa, recorded these occasional reversals. The limestone also contained the fossilized remains of millions of tiny sea creatures called foraminifera. In the course of several trips to Italy, Alvarez became interested in a thin layer of clay in the limestone that seemed to have been laid down around the end of the Cretaceous. Below the layer, certain species of foraminifera—or forams, for short—were preserved. In the clay layer there were no forams. Above the layer, the earlier species disappeared and new forams appeared. Having been taught the uniformitarian view, Alvarez wasn't sure what to make of what he was seeing, because the change, he later recalled, certainly "looked very abrupt."

  Alvarez decided to try to find out how long it had taken for the clay layer to be deposited. In 1977 he took a post at the University of California at Berkeley, where his father, the Nobel Prize–winning physicist Luis Alvarez, was also teaching. The older Alvarez suggested using the element iridium to answer the question.

  Iridium is extremely rare on Earth's surface but more plentiful in meteorites, which, in the form of microscopic grains of cosmic dust, are constantly raining down on the planet. The Alvarezes rea soned that if the clay layer had taken a significant amount of time to deposit, it would contain detectable levels of iridium, and if it had been deposited in a short time it wouldn't. They enlisted two other scientists, Frank Asaro and Helen Michel, to run the tests, and gave them samples of the clay. Nine months later, they got a phone call. There was something seriously wrong. Much too much iridium was showing up in the samples. Walter Alvarez flew to Denmark to take samples of another layer of exposed clay from the end of the Cretaceous. When they were tested, these samples, too, were way out of line.

  The Alvarez hypothesis, as it became known, was that everything—the clay layer from the scaglia rossa, the clay from Denmark, the spike in iridium, the shift in the fossils—could be explained by a single event. In 1980 the Alvarezes and their colleagues proposed that a six-mile-wide asteroid had slammed into Earth, killing off not only the forams but the dinosaurs and all the other organisms that went extinct at the end of the Cretaceous. "I can remember working very hard to make that 1980 paper just as solid as it could possibly be," Walter Alvarez recalled recently. Nevertheless, the idea was greeted with incredulity.

  "The arrogance of those people is simply unbelievable," one paleontologist told the Times.

  "Unseen bolides dropping into an unseen sea are not for me," another declared.

  Over the next decade, evidence in favor of an enormous impact kept accumulating. Geologists looking at rocks from the end of the Cretaceous in Montana found tiny mineral grains that seemed to have suffered a violent shock. (Such "shocked quartz" is typically found in the immediate vicinity of meteorite craters.) Other geologists, looking in other parts of the world, found small, glasslike spheres of the sort believed to form when molten-rock droplets splash up into the atmosphere. In 1990 a crater large enough to have been formed by the enormous asteroid that the Alvarezes were proposing was found, buried underneath the Yucatán. In 1991 that crater was dated and discovered to have been formed at precisely the time the dinosaurs died off.

  "Those eleven years seemed long at the time, but looking back they seem very brief," Walter Alvarez told me. '"Just think about it for a moment. Here you have a challenge to a uniformitarian view point 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."

  Today, it's generally accepted that the asteroid that plowed into the Yucatán led, in very short order, to a mass extinction, but scientists are still uncertain exactly how the process unfolded. One theory holds that the impact raised a cloud of dust that blocked the sun, preventing photosynthesis and causing widespread starvation. According to another theory, the impact kicked up a plume of vaporized rock traveling with so much force that it broke through the atmosphere. The particles in the plume then recondensed, generating, as they fell back to Earth, enough thermal energy to, in effect, broil the surface of the planet.

  Whatever the mechanism, the Alvarezes' discovery wreaked havoc with the uniformitarian idea of extinction. The fossil record, it turned out, was marked by discontinuities because the history of life was marked by discontinuities.

  In the nineteenth century, and then again during World War II, the Adirondacks were a major source of iron ore. As a re
sult, the mountains are now riddled with abandoned mines. On a gray day this winter, I went to visit one of the mines (I was asked not to say which) with a wildlife biologist named Al Hicks. Hicks, who is fifty-four, is tall and outgoing, with a barrel chest and ruddy cheeks. He works at the headquarters of the New York State Department of Environmental Conservation in Albany, and we met in a parking lot not far from his office. From there we drove almost due north.

  Along the way, Hicks explained how, in early 2007, he started to get a lot of strange calls about bats. Sometimes the call would be about a dead bat that had been brought inside by somebody's dog. Sometimes it was about a live—or half-alive—bat flapping around on the driveway. This was in the middle of winter, when any bat in the Northeast should have been hanging by its feet in a state of torpor. Hicks found the calls bizarre, but beyond that, he didn't know what to make of them. Then, in March 2007, some colleagues went to do a routine census of hibernating bats in a cave west of Albany. After the survey, they, too, phoned in.

  "They said, 'Holy shit, there's dead bats everywhere,'" Hicks recalled. He instructed them to bring some carcasses back to the office, which they did. They also shot photographs of live bats hanging from the cave's ceiling. When Hicks examined the photographs, he saw that the animals looked as if they had been dunked, nose first, in talcum powder. This was something he had never run across before, and he began sending the photographs to all the bat specialists he could think of. None of them could explain it, either.

  "We were thinking, Oh, boy, we hope this just goes away," he told me. "It was like the Bush administration. And, like the Bush administration, it just wouldn't go away." In the winter of 2008, bats with the white powdery substance were found in thirty-three hibernating spots. Meanwhile, bats kept dying. In some hibernacula, populations plunged by as much as 97 percent.

  That winter, officials at the National Wildlife Health Center, in Madison, Wisconsin, began to look into the situation. They were able to culture the white substance, which was found to be a never before identified fungus that grows only at cold temperatures. The condition became known as white-nose syndrome, or WNS. White nose seemed to be spreading fast; by March 2008, it had been found on bats in three more states—Vermont, Massachusetts, and Connecticut—and the mortality rate was running above 75 percent. This past winter, white nose was found to have spread to bats in five more states: New Jersey, New Hampshire, Virginia, West Virginia, and Pennsylvania.

  In a paper published recently in Science, Hicks and several co-authors observed that "parallels can be drawn between the threat posed by W.N.S. and that from chytridiomycosis, a lethal fungal skin infection that has recently caused precipitous global amphibian population declines."

  When we arrived at the base of a mountain not far from Lake Champlain, more than a dozen people were standing around in the cold, waiting for us. Most, like Hicks, were from the DEC and had come to help conduct a bat census. In addition, there was a pair of biologists from the U.S. Fish and Wildlife Service and a local novelist who was thinking of incorporating a subplot about white nose into his next book. Everyone put on snowshoes, except for the novelist, who hadn't brought any, and began tromping up the slope toward the mine entrance.

  The snow was icy and the going slow, so it took almost half an hour to reach an outlook over the Champlain Valley. While we were waiting for the novelist to catch up—apparently, he was having trouble hiking through the three-foot-deep drifts—the conversation turned to the potential dangers of entering an abandoned mine. These, I was told, included getting crushed by falling rocks, being poisoned by a gas leak, and plunging over a sheer drop of a hundred feet or more.

  After another fifteen minutes or so, we reached the mine entrance—essentially, a large hole cut into the hillside. The stones in front of the entrance were white with bird droppings, and the snow was covered with paw prints. Evidently, ravens and coyotes had discovered that the spot was an easy place to pick up dinner.

  "Well, shit," Hicks said. Bats were fluttering in and out of the mine and in some cases crawling on the ground. Hicks went to catch one; it was so lethargic that he grabbed it on the first try. He held it between his thumb and forefinger, snapped its neck, and placed it in a Ziploc bag.

  "Short survey today," he announced.

  At this point, it's not known exactly how the syndrome kills bats. What is known is that bats with the syndrome often wake up from their torpor and fly around, which leads them to die either of starvation or of the cold or to get picked off by predators.

  We unstrapped our snowshoes and put on helmets. Hicks handed out headlamps—we were supposed to carry at least one extra—and packages of batteries; then we filed into the mine, down a long, sloping tunnel. Shattered beams littered the ground, and bats flew up at us through the gloom. Hicks cautioned everyone to stay alert. "There's places that if you take a step you won't be stepping back," he warned. The tunnel twisted along, sometimes opening up into concert-hall-size chambers with side tunnels leading out of them.

  Over the years, the various sections of the mine had acquired names; when we reached something called the Don Thomas section, we split up into groups to start the survey. The process consisted of photographing as many bats as possible. (Later on, back in Albany, someone would have to count all the bats in the pictures.) I went with Hicks, who was carrying an enormous camera, and one of the biologists from the Fish and Wildlife Service, who had a laser pointer. The biologist would aim the pointer at a cluster of bats hanging from the ceiling. Hicks would then snap a photograph. Most of the bats were little brown bats; these are the most common bats in the United States and the ones you are most likely to see flying around on a summer night. There were also Indiana bats, which are on the federal endangered species list, and small-footed bats, which, at the rate things are going, are likely to end up there. As we moved along, we kept disturbing the bats, which squeaked and started to rustle around, like half-asleep children.

  Since white nose grows only in the cold, it's odd to find it living on mammals, which, except when they're hibernating (or dead), maintain a high body temperature. It has been hypothesized that the fungus normally subsists by breaking down organic matter in a chilly place and that it was transported into bat hibernacula, where it began to break down bats. When news of white nose began to get around, a spelunker sent Hicks photographs that he had shot in Howe's Cave, in central New York. The photographs, which had been taken in 2006, showed bats with clear signs of white nose and are the earliest known record of the syndrome. Howe's Cave is connected to Howe's Caverns, a popular tourist destination.

  "It's kind of interesting that the first record we have of this fungus is photographs from a commercial cave in New York that gets about two hundred thousand visits a year," Hicks told me.

  Despite the name, white nose is not confined to bats' noses; as we worked our way along, people kept finding bats with freckles of fungus on their wings and ears. Several of these were dispatched, for study purposes, with a thumb and forefinger. Each dead bat was sexed—males can be identified by their tiny penises—and placed in a Ziploc bag.

  At about 7 P.M., we came to a huge, rusty winch, which, when the mine was operational, had been used to haul ore to the surface. By this point, we were almost down at the bottom of the mountain, except that we were on the inside of it. Below, the path disappeared into a pool of water, like the River Styx. It was impossible to go any further, and we began working our way back up.

  Bats, like virtually all other creatures alive today, are masters of adaptation descended from lucky survivors. The earliest bat fossil that has been found dates from 53 million years ago, which is to say 12 million years after the impact that ended the Cretaceous. It belongs to an animal that had wings and could fly but had not yet developed the specialized inner ear that, in modern bats, allows for echolocation. Worldwide, there are now more than a thousand bat species, which together make up nearly a fifth of all species of mammals. Most feed on insects; there are also bats
that live off fruit, bats that eat fish—they use echolocation to detect minute ripples in the water—and a small but highly celebrated group that consumes blood. Bats are great colonizers—Darwin noted that even New Zealand, which has no other native mammals, has its own bats—and they can be found as far north as Alaska and as far south as Tierra del Fuego.

  In the time that bats have evolved and spread, the world has changed a great deal. Fifty-three million years ago, at the start of the Eocene, the planet was very warm, and tropical palms grew at the latitude of London. The climate cooled, the Antarctic ice sheet began to form, and, eventually, about 2 million years ago, a period of recurring glaciations began. As recently as 15,000 years ago, the Adirondacks were buried under ice.

  One of the puzzles of mass extinction is why, at certain junctures, the resourcefulness of life seems to falter. As powerful as the Alvarez hypothesis proved to be, it explains only a single mass extinction.

  "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, of course, 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."

  Andrew Knoll, a paleontologist at Harvard, has spent most of his career studying the evolution of early life. (Among the many samples he keeps in his office are fossils of microorganisms that lived 2.8 billion years ago.) He has also written about more recent events, like the end-Permian extinction, which took place 250 million years ago, and the current extinction event.