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Lost World: Rewriting Prehistory-How New Science Is Tracing America's Ice Age Mariners
Cave of the Bears
"Watch your head," said paleontologist Tim Heaton, ducking as he led the way down into the fissure in the steep rock face, leaving the sunshine and warmth behind. It was cold, damp, and quiet. Underground, away from the droning of the big gasoline generator, there was only the barest murmur of seeping water. But we could see well enough. Thick electrical cables ran into the cave to a few lights that were strung along one side.
We were on Prince of Wales Island, Alaska, in the summer of 1999. The main chamber was tiny and cramped, only about ten feet wide, with a ceiling so low in places that we had to stoop. The rocky floor was wet and uneven, and the farthest nook was only about forty feet back from the entrance. Kneeling on the muddy floor of the chamber and scraping up dirt with a trowel was a slim young guy with a wispy black beard who turned to say hello. Kei Nozaki, from Japan, was one of the student assistants Heaton had brought up from the University of South Dakota for a season of fieldwork. Like us, Nozaki was wearing a caver's helmet and a rain suit over his clothes.
Off to the right, a second and much narrower tunnel sloped away into the shadows. "The cave branches here," said Heaton with the soft western twang of his native Utah. "This is what we call the 'Seal Passage,' because that's where we found so many of the seal bones. And it actually loops around and comes out at another entrance down the hillside a bit. It's got a tight little keyhole shape." I switched on my headlamp and flashlight and stepped down into the passageway to take a look.
Heaton wasn't exaggerating. The dank and constricted little gut had a symmetrical keyhole cross section all the way along the gentle downward grade to where it jogged out of sight maybe fifty feet away. From knee to head height the walls, glistening with moisture, had the shape of a round tube about three feet in diameter. Below that was a sort of lower extension, a slot barely wide enough to put one rubber boot past the other. This telltale keyhole shape resulted, Heaton explained, because initially, when the water table was high, a steady flow of ground water had dissolved the limestone over thousands of years, routing out a subterranean water pipe, a nearly perfect cylinder, what geologists call a "solution tube." At some later time, the water table dropped and water only flowed along the very bottom of the tube. This eroded the rock straight down from the center and carved out the lower part of the keyhole. Much of the limestone on the island, and elsewhere on the southeastern coast of Alaska, was riddled with similar tubes and passages. Some of the caves penetrate entire mountains and have never been fully explored — a caver's dream.
I figured I would make my way down the length of the seal passage and have a look at the other entrance, but it was so hard to squeeze one foot past the other in the tight slot that I soon had second thoughts. And then I discovered that I couldn't turn around. I was stuck in an awkward crouched position, with cold, slimy stone walls hemming me in on both sides. Being trapped in a mine or buried alive has always been one of my pet phobias. Little fingers of fear crept up my spine, even with Heaton right there, close behind. No, I decided, I did not really need to inspect the other end of that dark, narrow tunnel. I was forced to back my way slowly out and exhaled with relief when I was back in the main chamber.
Heaton chuckled at my discomfort. "I'm used to working under the adverse conditions of caves," he said. "This is my third big excavation on the island." He had done a lot of sport caving as a teenager in Utah — even meeting his wife Julie at a caving club there — and still went caving occasionally just for fun. His other hobby was being a ham radio operator. And, at about forty, he was in terrific shape: tall, lanky, and built like a marathon runner.
For Heaton, the difficulty of working in this accessible, relatively level cave was nothing. "There's one cave here on the island where you have to go headfirst down a tight vertical crawlway, which emerges at the top of a 150 foot cliff." Other caves have underground lakes and flowing rivers. There are tight spots where you have to take off your jacket to squeeze through; if you get stuck, nobody can help you. And if the battery-powered headlamp goes out, everything dissolves into stygian blackness. "I do some pretty hefty caving to get at some of the bones. Cave paleontology is a specialty. Even most paleontologists are not used to it. They'd get claustrophobic crawling through these muddy holes," he laughed.
But it's a handy skill to have in his profession. "There's lots of bones in caves." For one thing, animals can find shelter in caves, and those that hibernate, such as bears, use the caves as dens in winter. A big bonus for paleontologists is the excellent preservation of bones, teeth, antlers — anything made of calcium — in the alkaline environment of a limestone cave. "Bone doesn't preserve too well outside," said Heaton, pointing to the entrance. "You have the temperature and humidity fluctuations, and the acidity of the forest soil, but as you get inside, the bones become better and better preserved, and more common."
The main chamber where Nozaki was digging was called the "Bear Passage." It was a few bear bones Heaton had discovered years earlier, and the totally unexpected information they provided, that initially made this little cave more interesting to him than the many larger and more physically impressive ones on the island.
But it wasn't bear bones that had brought me here from my home in British Columbia; it was human bones and artifacts.
We went back out into the August sunshine, and Nozaki joined us for a break and to warm up from the chill of the cave's interior. Heaton shut down the generator, and we sat to talk among the fuel drums, buckets, hoses, and other clutter of the work site. We were on a south-facing slope in virgin forest of big hemlock and spruce. Heaton took off his helmet and ran his hand through closely cropped red hair. With the sun in his face, he warmed to the quirky tale of how this remote bear den with the official federal designation 49-PET-408 had become one of the most important ancient archaeological sites in North America.
And he might never have even inspected it if it hadn't been for the weather.
Heaton's plan that year was to spend only a couple of weeks on the island. His target was a high-elevation site called "Bumper Cave," which ran sixty-five feet back from the entrance in sparse subalpine forest high on the flanks of Calder Mountain, a bald rocky dome that loomed over the island's far north end. I had flown past this stark summit early that very morning in the stolid old Beaver float plane that brought me out from Ketchikan to Port Protection, population fifty. There were no roads connecting the settlement to the rest of the island, and no post office, either. Just a dock, a store, a little lodge, a fish plant, and a scattering of houses, all clinging like limpets to the rocky shore of a tiny sheltered cove.
Jim, a chunky, bearded guy, helped me unload my gear from the plane. Like a few other people who were hanging out on the dock, Jim fished a little for salmon with the small commercial fishing boat that was also his home for the summer. Come winter, he drove a taxi in New York City.
To get from Port Protection to 49-PET-408, I hired a lanky fellow named Bud, who was missing a few teeth and had gray hair that reached halfway down his back. He told me that he had moved up from the Lower Forty-Eight in 1972. He made ends meet mainly by cutting lumber for people with a small, portable sawmill, and collected old stone artifacts off the beaches as a hobby. We had to cruise a few miles around a jutting peninsula in an aluminum skiff with a sputtering outboard. Along the way, Bud took a slight detour to show me his favorite spot for finding ancient adzes and daggers made of a greenish stone, presumably by the Tlingit Indians before they first had contact with the Russians and other Europeans in the 1700s. The tide was low and, sure enough, dozens of sharp flakes of green-gray rock were lying among rounded cobbles near some grounded boom logs that were linked together by massive rusty chains. I was skeptical about some of the pieces of stone that he claimed were artifacts, but Bud just smiled knowingly. "Here," he said. "You're going to the cave. Show these to the archaeologists and see what they say." It turned out that he was right.
Bud dropped me off at a gravel beach that was tucked in behind a tangle of kelp. There was a little cluster of brightly colored tents in a sheltered spot above the beach, and just enough room for me to set up mine. But no one else was around; they were all up at the cave, working. From the beach campsite to the cave was a half hour's trudge through dense forest along a steep, muddy trail that climbed more than 400 feet from sea level. For safety, Heaton and his crew had rigged some of the nearly vertical rock faces with knotted ropes. I was panting and sweating by the time I reached the site. It was a hike that I would make morning and evening for the next five days.
Back in 1994, though, Heaton had no intention of hiking that mile-long trail; in fact, it did not exist yet. He and a colleague had assembled the equipment for their expedition up to Bumper Cave, including camping gear and food for at least ten days. They were even bringing along 1000 feet of fire hose, enabling them to run water from a stream to wash and screen the sediment from the cave for any tiny animal bones they might miss at first glance. Kevin Allred, the Alaska-based leader of the cave project, had discovered and mapped Bumper Cave the previous summer, and had regaled Heaton with the juicy details. It was just littered with bear skeletons, he said, probably seven or eight in all, some of them exquisitely preserved. Millennia-old bones from other caves on the island had already overthrown some long-held assumptions about the Ice Age distribution and migrations of both black bears and grizzlies. Heaton was excited by the prospect that Bumper Cave might round out the new and emerging picture.
But his arrival on the island coincided with the long Fourth of July weekend, which grounded the Forest Service helicopter that was to take him and his gear up the mountainside. Baichtal, the geologist, had arranged for him to stay at a Forest Service camp that was the cave project's home base. With comfortable old wooden bunkhouses and separate buildings for cooking and showers, all overlooking a sheltered arm of the sea, this was not exactly a hardship post. But then the coastal weather closed in, and the helicopter could not fly. Day after rainy and foggy day, Heaton was forced to wait, cooling his heels at the camp, a frustrating thing for a guy who hates to waste a moment.
Waking one morning to see the trees shrouded yet again in mist, he and Allred decided to take a side trip to another cave on the island's extreme northwestern tip that Allred had visited the year before. Allred had heard about it from a Forest Service surveying crew, who first noticed the dark opening in the hillside when they hiked through to plot out future logging roads. The cave's ceiling was so low that the initial designation 49-PET-408 eventually gave way to the moniker "On Your Knees Cave."
Allred and two colleagues had crawled through with their compass, inclinometer, and tape measure back in 1993. Later, they made a scale drawing for the cave project's files, and that might have been the end of it, except that they also noticed some animal bones, in particular the well preserved skeleton of a river otter. When he heard about it from Allred the following summer, Heaton wondered what else the cave might hold.
With the helicopter grounded, Heaton and Allred drove to the end of the main logging road and hiked through the woods out onto a peninsula called "Protection Head." The cave didn't look like much. Inside, it was as Allred had described it. There was the river otter, which was interesting. Gee, imagine an otter coming all this way up from the sea, Heaton said to himself. And there were a few larger bones lying exposed right on the surface. One of them, he thought, was the femur of a grizzly bear. This wasn't a surprise to Heaton. Grizzlies did not inhabit the island in modern times, although black bears did. And though it used to be thought that grizzlies never had, Heaton had been finding the bones of both grizzlies and black bears in many of the caves for years now.
Heaton put the visible bones into plastic bags, labeled them, noted their locations in his notebook, and returned to the Forest Service camp. Eventually the weather cleared, the helicopter took him and his partner up to Bumper Cave, and they collected a wealth of bear bones, which later proved to be from 7,200 to 11,600 years old. It was a highly successful, if short, season. As for On Your Knees Cave, Heaton wrote it off as having much less paleontological interest than many of the other caves on the island. All he had found, after all, were the otter skeleton and a few more bear bones.
His verdict would change drastically a few months later. He had sent off a minute sample of the grizzly bear femur to a specialized laboratory for carbon dating. The lab isolated perhaps a thousandth of a gram of bone protein, called collagen, and sent it on to a nuclear laboratory equipped with a high-energy linear accelerator linked to a mass spectrometer. By what is called accelerator mass spectrometry (or AMS) dating, individual ions of the radioactive carbon isotope, carbon 14, were counted. The results went back to the first lab for analysis.
Back in South Dakota, Heaton eventually received a carbon 14 date of 35,000 years for the bear femur, or three times as old as the oldest bear bone previously found on the island. This placed it well before the peak of the last glaciation. Bones from the other caves already showed that bears had inhabited the island in the final, waning years of the glaciation, around 12,300 years ago. Was it possible that they had survived there right through the most recent advance and retreat of the great ramparts of ice, from about 25,000 to 10,000 years ago? If so, the area was a glacial refuge, a sizable haven of life on the outer edge of what was for many millennia a largely sterile, frigid, and icebound coast.
These findings ran entirely contrary to what biologists and geologists had been saying. Most thought that the entire coast of southeastern Alaska, including the islands like Prince of Wales, had been smothered by ice, leaving no such refuges. In 1965, biologist David Klein undertook a study of mammal distributions in the islands of southeast Alaska and had proclaimed unequivocally: "During the [most recent] glaciation the present land areas of the coastal regions...were virtually completely overridden by ice. The now existing flora and fauna of the region have presumably become established in the 10,000 years since the recession of the ice." For decades, this remained the authoritative view.
Recently, though, a few scientists had begun to wonder. Even Heaton's earlier finds of bears dating to the very end of the Ice Age, from 10,000 to over 12,000 years ago, were a significant clue. Jim Baichtal had told the journal Science, "If bears were living here, then chances are pretty good that we were not overridden by a blanket of ice as the textbooks have been telling us."
And there was other evidence that pointed to the existence of Ice Age refuges. Grizzlies still inhabited islands farther north along the coast of Alaska. Several studies of their DNA by Gerald Shields and his colleagues at the University of Alaska showed that these grizzlies were more closely related to polar bears than to any other currently living bears, including other grizzlies that still inhabited the adjacent mainland of Alaska. And this affinity was despite the fact that the intervening channels were not too wide for the bears to swim across. This suggested that the offshore grizzlies had spent a very long time evolving in genetic isolation. Polar bears, in turn, were thought to have evolved from brown bears, the genus to which grizzlies belong, probably on the Siberian coast. The most likely explanation for this overall pattern was that the offshore Alaska grizzlies had been cut off from contact with other grizzlies during the last glaciation in a coastal refuge, or refugium, as the scientists like to call it. And it would have to be quite large to support a separate breeding population of bears. Now, thought Heaton, the bones from On Your Knees Cave might be telling a similar story.
Heaton had already tossed ideas back and forth with a few geologists and archaeologists who thought there might have been an entire network of such offshore refuges along the North Pacific coast. He realized that the northwestern tip of Prince of Wales Island had not likely been a tiny, isolated pocket of ice-free land. To the west and north of Prince of Wales Island — and therefore farther away from the mainland coast with its massive ice sheet — were other very sizable islands. If the tip of Prince of Wales had been beyond the reach of the ice, major parts of those other islands would probably have been ice-free as well.
Although the Cordilleran ice sheet may have been a mile or more thick where it blanketed the higher mountains of the mainland coast, at its outer edges to the west it would have thinned significantly, and as it advanced it would have split into separate glacial flows that followed the paths of least resistance. So it would be wrong to picture a monolithic wall of ice fronting the sea, like the vertical blue cliffs of an ice shelf on the coast of Antarctica. What reached out among today's coastal islands to the then-lower sea level on the continental shelf would have been massive snouts of grimy gray ice, oozing their way downhill under the force of gravity like stiff molasses. Where there were mountains or high ridges on the islands, these frozen rivers, propelled by the weight of ice behind them at higher elevation on the mainland shore, would have followed the deeper channels between the islands to grind opportunistic paths around the obstructions. And, because of lowered Ice Age sea level, there would also have been land beyond those islands that blocked the glacial flow, out on the gently sloping continental shelf. This land is now under water. At the peak of the glaciation, though, it would have been dry and quite habitable.
Tom Ager of the U.S. Geological Survey (USGS) has been systematically tracing the glacial flows through the archipelago of southeast Alaska and pinpointing these formerly exposed areas of land on bathymetric charts. To the west of Dall, Coronation, and Baranof Islands, says Ager, there were a number of distinct glacial refuges, a few of them hundreds of square miles in size.
To Tim Heaton, all of this suggested that along with the bears, people might have lived in the area as well. If these people had camped, fished, and hunted on the shores of an extensive glacial refuge, much of their prime territory would be under water today. But the cave could have acted as a magnet to draw them inland and uphill to hunt the denning bears, so it might offer the best chance to find traces of these early coastal dwellers. If, that is, people were actually on Prince of Wales or neighboring islands back in Ice Age times. Heaton was excited at the prospect of making a discovery that could overturn some of the most strongly held and long-established ideas about North American prehistory. He could hardly wait for the next summer, to get back to On Your Knees Cave and investigate further.
It would be two years before the human story of On Your Knees Cave began to unfold. And when it did, it went a long way to unravel the secrets of the late Ice Age coastal world.
But not all the pieces of the puzzle would come from the efforts of a lone paleontologist gathering bones in an Alaskan cave. Some would be dredged from the sea floor by a research ship in the Queen Charlotte Islands of British Columbia, a few hundred miles to the south. The bones of an extinct mouse species on an island off California would offer mute testimony about when an Ice Age woman died in a swampy canyon. Important information would come from a geologist who determined the length of time that a line of erratic boulders hundreds of miles long had been exposed to the sky. Other pieces of evidence, including razor-sharp microblades of volcanic glass, would be unearthed by young Tlingit and Haida Indians, the likely descendants of the very ancient people who left those artifacts behind.
It was a heady experience for those involved in the search. They knew that what they might find could revolutionize our most fundamental self-image. For we have been accustomed to thinking of ourselves as a species in terrestrial terms: evolving in the savanna of Africa; hunkering in caves in Europe; gradually spreading overland through Asia; and finally trekking dry-shod across a land bridge at the Bering Strait into the Americas while preying upon big Ice Age animals. But if the scientists on the Pacific coast were right, we also became bold seafarers at a very early date, maritime people who built boats and braved the stormy and icebound shores of the North Pacific. And we lived not just from hunting mammoths and huge bison, but also from spearing sea mammals, from fishing, and from gathering shellfish and seaweed. This would be quite a different picture, yet one that is just as heroic and compelling.
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