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Evidence Piling Up for Coastal Migration Route

A few summers ago, archaeologist Joanne McSporran saw a sharp black rock in a pile of gravel pulled from the seafloor off British Columbia. The rock, an ancient knife, is another hint that the first Americans may have funneled onto the continent along the Pacific coast.

Anthropologists have long argued that the first human residents of North America scampered between two massive ice sheets through the interior of North America, moving from the Bering Land Bridge to the Great Plains of Canada and the U.S. Some researchers now believe that the Pacific coast in Alaska and British Columbia may have been free of ice before the end of the last ice age, allowing humans to pick their way along the coast from Asia to the New World.

McSporran found the stone tool when she was working as a volunteer on a project led by her husband, Daryl Fedje, an archaeologist with Parks Canada in Victoria, B.C. They were searching the sea bottom off the Queen Charlotte Islands, just south of Alaska, when they found the stone knife about 150 feet below the surface of the ocean.

Why look underwater for signs of ancient people? The scientists knew that the ocean floor just offshore the islands was dry land during the ice age, which lasted from about 25,000 to 11,000 years ago. During the peak of the ice age, about 17,000 years ago, massive ice sheets trapped enough of Earth's water that sea level was more than 300 feet lower than it is today. As the ice age waned, glaciers and ice caps melted, and the oceans rose to near-modern levels around 9,000 years ago.

Fedje and his colleague Heiner Josenhans of the Geological Survey of Canada used high-resolution sonar to map the surface of the sea floor off the Queen Charlotte Islands. Their map shows old river channels, lakes, bluffs and ridgetops that were above water at the end of the last ice age.

Fedje and Josenhans studied the seafloor map and chose a number of spots to lower a "clamshell-grab sampler," which looks like a coin-operated crane used to grab stuffed animals but weighs about a ton more. The sampler plucked the stone knife from an area Fedje chose because it looked like a nice campsite.

"The stone tool was sitting near the edge of a terrace that would have been dry land above a riverbed 10,000 years ago," he said.

The researchers also pulled up a rooted pine stump from a forested landscape now drowned beneath 500 feet of ocean. They dated the pine stump to about 12,200 years ago.

The Canadians' discovery of the stone tool and the ancient pine tree off the Queen Charlotte Islands strengthens the notion that early settlers of the Americas may have skirted North America's ice like kayakers do today, traveling from beach to beach between glaciers.

Findings by other researchers also support what archaeologists call "the coastal migration hypothesis." Timothy Heaton of the University of South Dakota found leg bones of brown and black bears that dated to 40,000 years ago in a Southeast Alaska cave. According to the older theory of how people populated the Americas, an ice sheet should have prevented any bears from living there at the time. Heaton and Fred Grady discovered human bones that are 9,200 years old in another Southeast cave. Though the bones-the oldest ever found in Alaska-date to a time when the ice had retreated, obsidian tools found near the bones hinted that people had lived on the Pacific coast for some time.