Читать книгу Spying on Whales - Nick Pyenson - Страница 13

Imagine floating above the great tapered tail of South America from space, seeing it stripped of clouds, ice, soil, and water so that the geologic world beneath is made visible. The familiar outline of the continent rises in stark, jagged relief. The high spine of the Andes is draped in red and gray bands to the east, toward Argentina, and ochers and sands cover Chile to the west. From this vantage, the cone of South America is locked in by a jigsaw puzzle of oceanic plates, and a surprisingly deep, dark cut mars its western boundary.

This incision marks the border between the Nazca and South American tectonic plates, where the lip of the former inexorably and slowly rolls under the edge of the latter. This action uplifts what was once seafloor, carrying ancient organisms buried in it—extinct whales included—slowly to dry land on the western edge of South America. This tectonic motion, called subduction, eventually yields mountain chains like the Andes over geologic time. But at the scale of human lifetimes, subduction can cause megathrust earthquakes that convulse entire cities, maroon fishing boats, and kill thousands in a span of seconds.

In 1835 a young Charles Darwin observed the outcome of this very process along the coast of Chile, near Concepción. Three years into its round-the-world voyage, the HMS Beagle had rounded the horn of Tierra del Fuego and made its way up the west coast of South America. Darwin was ashore when the earthquake started. A crescendo over the course of hours allowed most of the residents of Concepción to flee and limited the scope of fatalities to a few dozen people. Aftershocks rattled terrified locals for several days thereafter. Darwin later surveyed the devastation in Concepción firsthand, noting that most of the city was flattened, burned, or flooded by an accompanying tsunami—and that the entire shoreline of the harbor had risen several feet, stranding limpets and starfish. Darwin surmised that these catastrophic effects were connected with the volcanic eruptions he had observed during earlier forays hundreds of miles south near Chiloé. Darwin suspected that volcanic eruptions, the sudden uplift of coastlines, earthquakes, and tsunamis were linked by a common underlying mechanism. His intuitive guess was more right than he could have known; they are all consequences of subduction—the jerky slippage of great masses of tectonic plates against one another—and the central process that underpins the idea of plate tectonics.

Plate tectonics is a very young idea about how the Earth works. Until the late twentieth century, geology textbooks did not have a clear answer for why South America’s eastern edge fit so nicely with the west coast of Africa, which is a bit like launching moon-bound rockets without knowing Newton’s physics. Eventually scientists discovered that convection currents from deep inside the Earth drive the fragmented crust of the Earth’s rocky surface into constant motion, over geologic time. Every continent, and the ocean plates between them, floats on a vast, molten, and churning globe. The idea of plate tectonics also neatly explains a variety of patterns in the fossil record, including why so many plants and extinct animals across the southern continents look so similar—namely because they were once, a hundred million years ago, living together on a larger continental mass that has since broken apart.

Before he started thinking about evolution, Darwin was a geologist, one with a long view of history and the planet. Deep Time was a new idea when Darwin roamed the South American cone. What he saw there—the earthquake at Concepción, petrified forests in the high Andes, and fossils of extinct land mammals in Patagonia—resonated with the concept of an unfathomably old planet, one that had actually weathered many billions of years, time enough for the power of selection to yield finches, tortoises, and whales.

Darwin spent his last days in South America on horseback in the Atacama Desert of Chile, geologizing away at any exposure of inner Earth while en route to meeting the Beagle, which was moored along the northern coast near the town of Caldera. From there he headed north and westward by sea, eventually to the Galápagos Islands. Textbooks celebrate Darwin’s few weeks on the Galápagos but tend to minimize the fact that he spent two years in the South American cone. He never returned to Chile, but his social network continued the work he had begun. Correspondences born out of a shared love for the land, and scientific questions about it, roused a generation of Europeans who decamped for its rugged, open landscapes. The result is a testament to the strength of friendships that can transcend generations: they established the first centers of learning in Chile, including a national museum, whose collections still hold fossils that Darwin collected over 180 years ago. When you open up museum drawers and handle those specimens, you realize that these physical objects connect scientists across centuries, anchoring the questions that we have about evolution on this planet.

Sweeping offshore of the Atacama is the Humboldt Current, an enormous, ever-flowing body of water that cannot be discerned by the naked eye. Its namesake is a scientific figure of impressive breadth and accomplishment who preceded Darwin by decades—although Alexander von Humboldt never made it south of Lima, Peru. Today the Humboldt Current is renowned as one of the richest fisheries on the planet. Open any can of anchovies or sardines, and there’s a good chance that its contents came from the ocean current that stretches from Chilean Patagonia to Peru and the Galápagos.

Understanding how the Humboldt Current works, in the simplest terms, requires a step back to look at the coastal phenomenon of upwelling. When the Earth spins on its tilted axis, hot air rolls unevenly off the continents and transforms into trade winds over open ocean. These winds push hot water away from coastlines, and in its place arise enormous spirals of nutrient-rich water from the ocean’s depths, in a process called upwelling. Westerly coastlines across the world, from California to Chile to Angola, all share the right set of geographic features for this process. Upwelling forms the foundation for rich and productive ocean food webs because of the nutrients brought up from the deep: ocean water at the surface generally has enough oxygen, but it’s upwelling that carries nitrogen and phosphorus into shallower waters and enriches them by fertilizing both light-fixing phytoplankton and their consumers, zooplankton. The oceans may be vast, but upwelling creates specific places where these tiny organisms gather. Where there’s food to eat, that’s where whales, sardines, and penguins all want to be.

And if you’re a whale paleontologist, you want to be on the coast nearby, where upwelling and subduction combine in a perfect way. Upwelling gives us whales, and ultimately their remains—whale bones—to look for, while subduction uplifts ancient seafloors to dry land. Along with these two processes, the accident of the Atacama’s latitude makes the entire desert a gift for scientists seeking rocks: it’s devoid of grass, trees, and the blacktop of civilization. Arid and exposed badlands allow erosion to exhume the remains of ancient whales locked in rock without the interference of soil or tree roots.

Erosion helps, but paleontologists also have to find the right kind of rocks. Of the three categories, igneous, metamorphic, and sedimentary, for fossil whales only sedimentary rocks will do. Whales don’t preserve well in volcanic lava flows, and fossils hardly ever survive the tremendous heat and pressure that creates metamorphic rocks dozens of miles beneath the Earth’s surface. Among the array of sedimentary rocks, the most promising ones include mudstones, representing offshore seafloors, and sandstones, representing nearshore ones. Thanks to uplift, the only way to find fossils in the Atacama involves rolling across washes and mesas by foot or truck, finding these rocks, and keeping an eye out for a glint of bone. Whale bones tend to be relatively big, after all.

Since Darwin’s time, many thousands of bits of bone and teeth have been collected from the Caldera Basin, some ending up in natural history museums such as the one in Santiago, founded by Darwin’s correspondents. Fossil collections from Caldera consist almost entirely of fragments of skulls, limb bones, and teeth—never complete skeletons. But the little they show suggests that the Humboldt Current of the past was different: familiar species such as whales, sharks, and sea turtles lived alongside bizarre extinct ones, including nightmarish bony-toothed seabirds, long-snouted aquatic sloths, and school bus–size predatory sharks. When I started to contemplate working in the Atacama, the problem was that we didn’t have precise ages on all of these fossils in hand—we needed one complete chronicle of rocks in the Caldera Basin. Minimally we needed to identify the correct succession of layers these fossils came from, identifying oldest to youngest; at best, we hoped to pin down the ages of each fossil-bearing layer with numerical geologic dates. Once that context was arranged, we would be able to chart the rise and fall of each species over millions of years, against the backdrop of broader changes to ocean temperature, sea level, and circulation. Wear a geologist’s hat, find whale bones, and figure out the story of how the Humboldt Current’s ecosystem came to be.

After years of planning, correspondence, and false starts, I found myself sweating in the glare of the Atacama sun. I paused from scanning a geologic map of the Caldera Basin, spread across the hood of the Toyota pickup, and squinted, hoping to catch a glimpse of people summiting the flat top of a mesa in the distance. The harshness of the white light pinched my vision, split between the patchwork of colors on the map before me and the pale-blue dome above my head. I was frustrated, my mind elsewhere. We were late. The students on the field team hadn’t reconvened at the agreed-to time and we needed to keep moving.

We had followed the whale bone trail in the Atacama, and the trail led us straight into fault lines—many of them. Finding fossils wasn’t exactly our problem. Instead, it was their context. We were having a difficult time piecing together the succession of rock layers in which we were finding them. As tectonic processes uplifted ancient seafloors, they also broke them up, like a layer cake dropped on the floor. Consequently, deciphering the specific old-to-young sequence of layer upon layer of rock was complicated by long, vertical fractures that displaced the layers up and down relative to one another. We tend to think of geologic faults as stretching across hundreds of miles, and that’s certainly true for some of them. But they also manifest locally, in a rock outcrop that may be no broader than the side of a house. In the Caldera Basin, faulting sometimes created a jumbled layer of rock rather than a neat stack.

With boots on the ground, building a single chronology of rocks meant finding specific places where we could measure the thickness of the rock layer in a repeatable way, using a simple geologic tool called a Jacob’s staff. We would also note the composition, color, and texture of each rock layer. Occasionally we would also hammer out a sample of the most promising rocks—usually the ashes—in the hope of finding tiny volcanic grains that would yield precise geologic dates back in a laboratory. Through this slow, exacting work of measuring, describing, and sampling, we hoped to pin down actual dates in geologic time for enough layers in the sequence to understand the succession of different extinct species, whales and otherwise, that once lived in the Humboldt Current.

Back at the truck, however, I wasn’t thinking about geologic maps or envisioning layers of fossil whales captured through time. Instead, I was thinking about hours wasted, miles away from the air-conditioned convenience and sprawling desk work within my museum’s walls. I thought about all of the effort and time—coordinating airfares and truck rentals, pushing permits along, accounting for family and professional commitments. As the students crested the mesa, I waved at them. What I really wanted to do was slam on the truck’s horn until it was out of air.

Carolina Gutstein, my friend and colleague, then finishing her doctoral degree, stood with me at the truck. “You know, you can’t just rush people,” she leveled, without hesitation, sizing up my agitation like a sibling. “Trying to make things go faster here is only going to make them go a lot slower.” I laughed ever so slightly but stopped when I turned to look at her. Caro’s face was dispassionately still, her mountaineering sunglasses reflecting a stereo double of my own weary glance. I looked down in frustration, back toward the map on the hood, and exhaled. When I glanced her way again, she smiled, breaking the tension. “Why don’t we go see all those whales at Cerro Ballena?” she offered. “I’ll call Tuareg to show us around. He and Jim are over there now. You’re not going to believe it.”

Actually, I thought that I had good reason not to believe it, especially if it involved the man who calls himself Tuareg. His real name is Mario Suárez, and he is probably the single best fossil finder I have ever known. He demurs when asked, but Mario’s self-appointed nickname is clearly meant to evoke the stoic Berber people of the Sahara—an image he routinely betrays by losing his cell phone (he has lost more than a dozen) and completely going AWOL when needed (usually found at the nearest bakery). But at the time, we were strictly in his domain, working under his collecting permit, which he held as curator at the local paleontology museum in the town of Caldera.

Tuareg had e-mailed me earlier that year about a place he started to call Cerro Ballena, where he said complete whale skeletons had been found, but I’d had a hard time discerning much from afar. I remembered having seen the site on a past visit, a sloping road cut of the Pan-American Highway that trenched through a layer cake of orange and tan marine rocks. The only fossils I had noted were a smattering of skull bones from a large whale, likely a baleen one. Locals had tried tunneling out the bones, unsuccessfully, next to graffiti carved in the soft sandstone. None too auspicious. Fossil whale skulls are sometimes a jumble of broken bones that hardly make sense at the rock outcrop and require care and study back at a laboratory. Also, they almost always involve heavy logistics that simply outstripped our time, our resources, and, to be frank, my motivation.

Caro’s suggestion reminded me of that whale skull we had seen together by the side of the road, although I was only burdened by the recollection to a point. If we had more time, maybe we could collect it, but we had to make hard decisions on the use of our time. We were in the Atacama to understand the evolution of the Humboldt Current ecosystem, as read from layers of fossils from dozens of species across time—doing so offered the chance to find out much more than a single broken-up baleen whale skull could ever tell us. Constructing a single stratigraphic column from the stacks of rocks across miles of fractured desert terrain was something reasonable and feasible to achieve during a single field season, if not particularly sexy. I was also on the hook to deliver publications out of our work, as a foundation for future collaborations. As it turned out, I had no clue how wrong I was about the importance of that broken-up skull at the side of the road, nor a hint about the scope of what it represented.

If I was ambivalent about seeing Tuareg, at least I was buoyed by the thought of reuniting with Jim Parham. Jim is a like-minded scientist, a friend, and a terrific sounding board. His finely tuned bullshit detector always checked my field decisions about logistics. Earlier that day, we had split the field team in two to maximize our time: Caro and I took the students to the south, while Jim and Tuareg went north to Cerro Ballena. “I really don’t think we both should be in the same truck as Tuareg,” I said to Jim at breakfast. “Oh—just as a matter of sanity,” he assented.

When Jim, Caro, and I had visited Cerro Ballena with Tuareg several years earlier, we’d referred to its location as “that road cut next to Playa Pulpos,” taken from the nearest highway sign. By late 2010, it had become Cerro Ballena—literally “whale hill” in Spanish—if only because of global geopolitics, in this dusty part of the Atacama. In the past few decades, Chile’s geologic resources have become prized targets for extraction by the mining industry, and accommodating large mining machines has meant road widening along remote parts of the Pan-American Highway. An environmental-impact study at Cerro Ballena concluded that further expansion would very likely uncover more fossils. Nevertheless, a road-construction company was green-lighted to begin widening the highway. To comply, the company enlisted Tuareg and his museum for assistance, with Chile’s strong natural patrimony laws ensuring that any fossils would be saved. It was then that Tuareg had started sending me clipped e-mails and shaky videos from the site, not exactly adequately conveying the message of what was happening there. Besides, it was Tuareg—hard to pull out the facts from hyperbole.

When Caro and I arrived, Tuareg and Jim were pacing about the quarry. Large black felt tarps dotted the desert floor every dozen feet, stretching north and south. I ambled up to Jim. “Dude,” he said in a low voice, telling me everything I needed to know in a single word. “This is not the Playa Pulpos that we saw two years ago.” Everyone gathered to follow as Tuareg walked from tarp to tarp, rolling each one backward. My mouth fell open as I absorbed the fact that every tarp covered at least one complete whale skeleton, and sometimes several on top of one another. Every black tarp, dozens spread up and down the road-cut quarry, demarcated a whale skeleton. The sheer density of complete skeletons outstripped everything I thought that I knew about how whales get preserved as fossils.

The skeletons, some thirty feet long, were almost all complete in a way that fossil whales hardly ever are, nose to tail. Many looked as if the creature had died in place, carefully turned on its back, and then been pressed flat over geologic time, like a preserved flower. Skulls were easy to spot, their triangular projections and bowed jawbones at the end of a trail of bricklike vertebrae. Rib cages collapsed toward tails, like gigantic Slinkys. In many skeletons, the ribs were still adorned with shoulder blades connected to arms and even finger bones. The fossil whales at this site were jaw-droppingly complete. And it made no sense that there were so many, so close together. I couldn’t think of any other field site of fossil whales like it.

I was stunned. Tuareg gabbed away with a positively gleeful Caro and her students. I walked over to where Jim stood at the south end of the quarry, taking photos and rubbing sediment between his fingers. We silently watched the sun slipping over the horizon, evening cloud banks bringing a cool wind. In the distance, a single round peak—El Morro, a weathered mound of igneous rock—capped the view.

“It’s over,” Jim said, flatly. I looked north and south across the entire quarry, more than a football field in length. I knew exactly what he meant: anything we had thought about doing needed to make room for this site and the several dozen skeletons that stretched up and down the hill in each direction. Measuring the stratigraphic columns across the Caldera Basin, slotting in all of the fossils we already knew about, deciphering that geologic map full of faults—it all needed to wait. My hours and hours of planning had focused on a sure thing, returning with bags of rock samples and with notebooks full of the makings of promised papers. Entire whale skeletons were not part of that plan, certainly not dozens of them.

I breathed in, anxious and unsure. I was frustrated with myself for not listening to Tuareg more carefully earlier on, paralyzed by the enormity of the scene in front of me. At the same time, part of me recognized that the scope of the site, with its dozens of perfect whale skeletons, was undeniably significant—and I had an open invitation to be one of the first ones to study a place like nowhere else, as far as I knew, on the planet. It was vexing and tantalizing; it was a kind of Pandora’s box, and we’d just seen it crack open.

“I know,” I said. “What are we going to do?”