When Did Humans Come to the Americas?
When Did Humans Come to the Americas?
Recent scientific findings date their arrival earlier than ever thought, sparking hot debate among archaeologists
Source - http://www.smithsonianmag.com/science-nature/When-Did-Humans-Come-to-the-Americas-187951111.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+smithsonianmag%2Fhistory-archaeology+%28History+%26+Archaeology+%7C+Smithsonian.com%29
Most analyses of contemporary and ancient human DNA suggest that America’s first immigrants came from Asia. They traveled over a land bridge or along the coast. An alternative theory is that members of Europe’s Solutrean culture voyaged to the East Coast. (5W Infographics)
For much of its length, the slow-moving Aucilla River in northern Florida flows underground, tunneling through bedrock limestone. But here and there it surfaces, and preserved in those inky ponds lie secrets of the first Americans.
For years adventurous divers had hunted fossils and artifacts in the sinkholes of the Aucilla about an hour east of Tallahassee. They found stone arrowheads and the bones of extinct mammals such as mammoth, mastodon and the American ice age horse.
Then, in the 1980s, archaeologists from the Florida Museum of Natural History opened a formal excavation in one particular sink. Below a layer of undisturbed sediment they found nine stone flakes that a person must have chipped from a larger stone, most likely to make tools and projectile points. They also found a mastodon tusk, scarred by circular cut marks from a knife. The tusk was 14,500 years old.
The age was surprising, even shocking, for it suddenly made the Aucilla sinkhole one of the earliest places in the Americas to betray the presence of human beings. Curiously, though, scholars largely ignored the discoveries of the Aucilla River Prehistory Project, instead clinging to the conviction that America’s earliest settlers arrived more recently, some 13,500 years ago. But now the sinkhole is getting a fresh look, along with several other provocative archaeological sites that show evidence of an earlier human presence in the Americas, perhaps much earlier.
Which is why I found myself on the banks of the Aucilla with Michael Waters, director of the Center for the Study of the First Americans at Texas A&M University. A tall, unassuming 57-year-old, with an easy confidence honed during more than 30 years in the field, he had organized archaeologists and divers to gather more evidence of the sinkhole’s role in prehistory. “This site is as old as anything in North America,” Waters said. “The context is fine, and the dating is fine, but people just looked at it and said, ‘Hmm, that’s interesting,’ and that was it. It had a lot of potential, but it was in limbo. We’re here to confirm the earlier work, and if we’re lucky, we’ll find some more artifacts.”
Waters’s team, led by Texas A&M underwater archaeologist Jessi Halligan, worked at the Page-Ladson sink, named for Buddy Page, who discovered it, and John Ladson, the property’s owner. The sink lies 30 feet below the opaque surface of the Aucilla, which, following heavy rains, was dyed nearly black by humus from the hardwood hammock. Fish were jumping in the water, while birds, turtles and the occasional gator patrolled nearby. Were it not for Halligan’s divers, there would be no human presence and the silence would be absolute.
Underwater archaeological sites are staked out and marked in meter-square quadrants, just like open-air excavations. The mud, troweled away by one diver, was fed into the mouth of a four-inch suction dredge held by a second diver. The dredge discharged into a pair of mesh screens mounted on a skiff moored in midstream. Big pieces—stones, bones, leaves and perhaps human artifacts—collected on the top screen, a quarter-inch mesh, and the small stuff was caught by the sixteenth-inch mesh below.
First the researchers had to clear the site of the detritus that had accumulated in the 15 years since the first excavation ended. Then, to reach the most promising level, divers removed a ten-foot layer of clay that overlay it. The work was tedious—“like diving in dark roast coffee,” said James Dunbar, an archaeologist and member of the original Aucilla team who’d returned for a second look—but the blanket of sediment guaranteed the site’s integrity. Everything below the sediment was as old as the people who left it there. In the oxygen-deprived deposits within the Aucilla mud, nothing decays.
Working in the Stygian gloom with lamps and suction pumps, the divers unearthed a number of small bone fragments, the fist-size vertebra of a large mammal and a manhole cover-size shoulder blade that might have belonged to the same mastodon whose tusk bore the cut marks of the ancient hunters. Also recovered in the fine-mesh screen were many pounds of mastodon digesta, the remains of vegetation that the six-ton beast ground to a mulch-like texture and swallowed.
The observations the researchers made in their days at the sinkhole validated the original excavation. (And on a subsequent expedition they found more mastodon bones.) Each new discovery generated fresh enthusiasm. “All we need now,” said Halligan, “are more human artifacts.”
About 100,000 years ago, modern human beings started spreading out from their initial homeland in Africa to occupy Europe, Asia and, by sea, even Australia, displacing or absorbing Neanderthals and other archaic hominid species. That diaspora took about 70,000 years, and when it was completed our ancestors stood triumphant.
The peopling of the Americas, scholars tend to agree, happened sometime in the past 25,000 years. In what might be called the standard view of events, a wave of big game hunters crossed into the New World from Siberia at the end of the last ice age, when the Bering Strait was a land bridge that had emerged after glaciers and continental ice sheets froze enough of the world’s water to lower sea level as much as 400 feet below what it is today.
The key question is precisely when the migration occurred. To be sure, there were constraints imposed by North America’s glacial history. Researchers suggest that it happened sometime after gradual warming began 25,000 years ago during the depths of the ice age, but well before a severe cold snap reversed the trend 12,900 years ago. Early in this window, when the weather was very cold, migration by boat was more likely because immense expanses of ice would have turned an overland journey into a nightmarish ordeal. Later, however, the ice receded, opening up plausible land bridges for trekkers coming across the Bering Strait.
For decades the most compelling evidence of this standard view consisted of distinctive, exquisitely crafted, grooved bifacial projectile points, called “Clovis points” after the New Mexico town near where they were first discovered in 1929. With the aid of radiocarbon dating in the 1950s, archaeologists determined that the Clovis sites were 13,500 years old. This came as little surprise, for the first Clovis points were found in ancient campsites along with the remains of mammoth and ice age bison, creatures that researchers knew had died out thousands of years ago. But the discovery dramatically undermined the prevailing wisdom that human beings and these ice age “megafauna” did not exist in America at the same time. Scholars flocked to New Mexico to see for themselves.
The idea that the Clovis people, as they came to be known, were the first Americans quickly won over the research community. “The evidence was unequivocal,” said Ted Goebel, a colleague of Waters at the Center for the Study of the First Americans. Clovis sites, it turned out, were spread all over the continent, and “there was a clear association of the fauna with hundreds, if not thousands, of artifacts,” Goebel said. “Again and again it was the full picture.”
Furthermore, the earliest Clovis dates corresponded roughly to the right geological moment—after the ice age warming, before the great cold snap. The northern ice had receded far enough so incoming settlers could curl around to the eastern slope of North America’s coastal mountains and hike south along an ice-free corridor between the cordilleran mountain glaciers to the west and the huge Laurentide ice sheet that swaddled much of Canada to the east. “It was a very nice package, and that’s what sealed the deal,” Goebel said. “Clovis as the first Americans became the standard, and it’s really a high bar.”
When they reached the temperate prairies, the migrants found an environment far different from what we know today—both fantastic and terrifying. There were mammoths, mastodons, giant sloths, camels, bison, lions, saber-toothed cats, cheetahs, dire wolves weighing 150 pounds, eight-foot beavers and short-faced bears that stood more than six feet tall on all fours and weighed 1,800 pounds. Clovis points, finely made and strong, were well suited for hunting large animals.
The hunters spread through the United States and Mexico, the story went, pursuing prey until too few animals remained to support them in the last cold snap. Radiocarbon dates show that most of the megafauna became extinct around 12,700 years ago. The Clovis points disappeared then as well, perhaps because there were no longer any large animals to hunt.
The Clovis theory, over time, acquired the force of dogma. “We all learned it as undergraduates,” Waters recalled. Any artifacts that scholars said came before Clovis, or competing theories that cast doubt on the Clovis-first idea, were ridiculed by the archaeological establishment, discredited as bad science or ignored.
Take South America. In the late 1970s, the U.S. archaeologist Tom D. Dillehay and his Chilean colleagues began excavating what appeared to be an ancient settlement on a creek bank at Monte Verde, in southern Chile. Radiocarbon readings on organic material collected from the ruins of a large tent-like structure showed that the site was 14,800 years old, predating Clovis finds by more than 1,000 years. The 50-foot-long main structure, made of wood with a hide roof, was divided into what appeared to be individual spaces, each with a separate hearth. Outside was a second, wishbone-shaped structure that apparently contained medicinal plants. Mastodons were butchered nearby. The excavators found cordage, stone choppers and augers and wooden planks preserved in the bog, along with plant remains, edible seeds and traces of wild potatoes. Significantly, though, the researchers found no Clovis points. That posed a challenge: either Clovis hunters went to South America without their trademark weapons (highly unlikely) or people settled in South America even before the Clovis people arrived.
There must have been “people somewhere in the Americas 15,000 or 16,000 years ago, or perhaps as long as 18,000 years ago,” said Dillehay, now at Vanderbilt University.
Of the researchers working sites that seemed to precede Clovis people, Dillehay was singled out for special criticism. He was all but ostracized by Clovis advocates for years. When he was invited to meetings, speakers stood up to denounce Monte Verde. “It’s not fun when people write to your dean and try to get you fired,” he recalled. “And then your grad students try to get jobs and they can’t get jobs.”
The Monte Verde site gained wider acceptance after a panel of well-known archaeologists visited it in 1997 and reached a consensus. Dillehay was pleased that the panel had verified the integrity of his team’s work, “but it was a small group of people,” he said, meaning others in the profession continued to harbor doubts.
Two years later, an independent archaeologist, Stuart Fiedel, denounced Monte Verde’s authenticity in Scientific American Discovering Archaeology. Dillehay “fails to provide even the most basic” information about the locations of “key artifacts” at Monte Verde, Fiedel wrote. “Unless and until numerous discrepancies in the final report are convincingly clarified, this site should not be construed as conclusive proof of a pre-Clovis occupation in South America.”
The skepticism lingers. Gary Haynes, a University of Nevada-Reno anthropologist and a Clovis advocate, is not convinced. “There are only a few artifacts, and no flakes,” he said of Monte Verde, citing some of Fiedel’s arguments. “There are a lot of things that have been interpreted as artifacts but don’t look like them. Many of the things may not be the same age, because it is difficult to know exactly where they were found in the site.”
Dillehay rebuffs the criticisms: “More than 1,500 pages were published on Monte Verde, which is five times more than were ever written on any other site in the Americas, including Clovis. All of the artifacts came from the same surface covered by the peat bog and they all made sense in terms of the site’s activities. The vast majority are flaked pebble tools, typical of South American unifacial technologies. North Americans impose their evaluations on South America without even knowing the data down south.” He went on, “Now the field has moved on, and there are numerous pre-Clovis sites that have come to the forefront.”