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 nineteen-thirties 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 co-authored 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 rain forest. 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 U.S., 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 the 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 between the second and the 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
nineteen-sixties, 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-nineteen-seventies, Walter Alvarez, a geologist at the Lamont
Doherty Earth Observatory, in New York, was studying the 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 then 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 the surface of
the earth, but more plentiful in meteorites, which, in the form of
microscopic grains of cosmic dust, are constantly raining down on the
planet. The Alvarezes reasoned 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 the 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
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.”
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 travelling 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 the Second World War, the
Adirondacks were a major source of iron ore. As a result, 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 ninety-seven per cent.
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 W.N.S. 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 seventy-five per cent. 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 D.E.C., 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 ziplock 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 U.S. 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 ziplock 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. [#unhandled_cartoon]
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 fifty-three million years ago, which is to say
twelve 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
land 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 two million years ago, a period of recurring
glaciations began. As recently as fifteen thousand 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. 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 naïvely 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 two hundred and fifty million years ago, and the current
extinction event.
Knoll noted that the world can change a lot
without producing huge losses; ice ages, for instance, come and go.
“What the geological record tells us is that it’s time to worry when the
rate of change is fast,” he told me. In the case of the end-Permian
extinction, Knoll and many other researchers believe that the trigger
was a sudden burst of volcanic activity; a plume of hot mantle rock from
deep in the earth sent nearly a million cubic miles’ worth of flood
basalts streaming over what is now Siberia. The eruption released
enormous quantities of carbon dioxide, which presumably led—then as
now—to global warming, and to significant changes in ocean chemistry.
“CO2
is a paleontologist’s dream,” Knoll told me. “It can kill things
directly, by physiological effects, of which ocean acidification is the
best known, and it can kill things by changing the climate. If it gets
warmer faster than you can migrate, you’re in trouble.”
In the end, the most deadly aspect of human activity may simply be the pace of it. Just in the past century, CO2
levels in the atmosphere have changed by as much—a hundred parts per
million—as they normally do in a hundred-thousand-year glacial cycle.
Meanwhile, the drop in ocean pH levels that has occurred over the past
fifty years may well exceed anything that happened in the seas during
the previous fifty million. In a single afternoon, a pathogen like Bd
can move, via United or American Airlines, halfway around the world.
Before man entered the picture, such a migration would have required
hundreds, if not thousands, of years—if, indeed, it could have been
completed at all.
Currently, a third of all amphibian species,
nearly a third of reef-building corals, a quarter of all mammals, and an
eighth of all birds are classified as “threatened with extinction.”
These estimates do not include the species that humans have already
wiped out or the species for which there are insufficient data. Nor do
the figures take into account the projected effects of global warming or
ocean acidification. Nor, of course, can they anticipate the kinds of
sudden, terrible collapses that are becoming almost routine.
I
asked Knoll to compare the current situation with past extinction
events. He told me that he didn’t want to exaggerate recent losses, or
to suggest that an extinction on the order of the end-Cretaceous or
end-Permian was imminent. At the same time, he noted, when the asteroid
hit the Yucatán “it was one terrible afternoon.” He went on, “But it was
a short-term event, and then things started getting better. Today, it’s
not like you have a stress and the stress is relieved and recovery
starts. It gets bad and then it keeps being bad, because the stress
doesn’t go away. Because the stress is us.”
Aeolus
Cave, in Dorset, Vermont, is believed to be the largest bat
hibernaculum in New England; it is estimated that, before white nose
hit, more than two hundred thousand bats—some from as far away as
Ontario and Rhode Island—came to spend the winter there.
In late
February, I went with Hicks to visit Aeolus. In the parking lot of the
local general store, we met up with officials from the Vermont Fish and
Wildlife Department, who had organized the trip. The entrance to Aeolus
is about a mile and a half from the nearest road, up a steep, wooded
hillside. This time, we approached by snowmobile. The temperature
outside was about twenty-five degrees—far too low for bats to be
active—but when we got near the entrance we could, once again, see bats
fluttering around. The most senior of the Vermont officials, Scott
Darling, announced that we’d all have to put on latex gloves and Tyvek
suits before proceeding. At first, this seemed to me to be paranoid;
soon, however, I came to see the sense of it.
Aeolus
is a marble cave that was created by water flow over the course of
thousands of years. The entrance is a large, nearly horizontal tunnel at
the bottom of a small hollow. To keep people out, the Nature
Conservancy, which owns the cave, has blocked off the opening with huge
iron slats, so that it looks like the gate of a medieval fortress. With a
key, one of the slats can be removed; this creates a narrow gap that
can be crawled (or slithered) through. Despite the cold, there was an
awful smell emanating from the cave—half game farm, half garbage dump.
When it was my turn, I squeezed through the gap and immediately slid on
the ice, into a pile of dead bats. The scene, in the dimness, was
horrific. There were giant icicles hanging from the ceiling, and from
the floor large knobs of ice rose up, like polyps. The ground was
covered with dead bats; some of the ice knobs, I noticed, had bats
frozen into them. There were torpid bats roosting on the ceiling, and
also wide-awake ones, which would take off and fly by or, sometimes,
right into us.
Why bat corpses pile up in some places, while in
others they get eaten or in some other way disappear, is unclear. Hicks
speculated that the weather conditions at Aeolus were so harsh that the
bats didn’t even make it out of the cave before dropping dead. He and
Darling had planned to do a count of the bats in the first chamber of
the cave, known as Guano Hall, but this plan was soon abandoned, and it
was decided just to collect specimens. Darling explained that the
specimens would be going to the American Museum of Natural History, so
that there would at least be a record of the bats that had once lived in
Aeolus. “This may be one of the last opportunities,” he said. In
contrast to a mine, which has been around at most for a few centuries,
Aeolus, he pointed out, has existed for millennia. It’s likely that bats
have been hibernating there, generation after generation, since the end
of the last ice age.
“That’s what makes this so dramatic—it’s breaking the evolutionary chain,” Darling said.
He
and Hicks began picking dead bats off the ground. Those which were too
badly decomposed were tossed back; those which were more or less intact
were sexed and placed in two-quart plastic bags. I helped out by holding
open the bag for females. Soon, it was full and another one was
started. It struck me, as I stood there holding a bag filled with
several dozen stiff, almost weightless bats, that I was watching mass
extinction in action.
Several more bags were collected. When the
specimen count hit somewhere around five hundred, Darling decided that
it was time to go. Hicks hung back, saying that he wanted to take some
pictures. In the hours we had been slipping around the cave, the carnage
had grown even more grotesque; many of the dead bats had been crushed
and now there was blood oozing out of them. As I made my way up toward
the entrance, Hicks called after me: “Don’t step on any dead bats.” It
took me a moment to realize that he was joking. ♦
