Fishing for the first Americans

Archaeology is moving underwater and along riverbanks to find clues left by the people who colonized the New World.

Emma Marris

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Calvert island photoEvidence of ancient Americans has turned up on Calvert Island in Canada. Keith Holmes

On 17 September, a catamaran will set off into the Pacific Ocean on a week-long cruise back to the Pleistocene. Laden with sonar instruments, the research vessel Shearwater will probe the ocean bottom to find places that were beaches and dry land more than 13,000 years ago, when the sea level was around 100 metres lower. The researchers are hunting for evidence that ancient people lived along this now-sunken coastline as they colonized the New World.

Meanwhile, other archaeologists are digging in the intertidal zone on a remote island off the shore of British Columbia in Canada, where the sea level has barely changed since the ice-age glaciers began to retreat. Since late last year, that team has found footprints and a tool that date back 13,200 years, making them some of the oldest human marks on the continent. Whoever left them had to have reached the island by boat.

Welcome to the newest wave of American archaeology: the idea that the first residents of the Americas came by sea, hugging the Pacific coast as they went south. This theory marks a sharp departure from the once-dominant hypothesis that Pleistocene hunters from Siberia migrated by foot across a land bridge to Alaska and then south into the heart of North America. This route opened up only when the vast sheets of ice covering the continent had melted enough to permit passage. It was thought that these first migrants made the distinctive stone spear tips called Clovis points, which began appearing at sites in the interior of North America around 13,000 years ago.

There has long been evidence that others reached the New World at least 1,000 years earlier. But only in the past decade have archaeologists accumulated enough evidence to abandon the Clovis-first model (see Nature 485, 30–32; 2012). Some of the earliest human sites in the Americas date to well before a corridor opened up between the ice sheets, which is forcing researchers to explore the idea that New World colonizers skirted the coastline. Travelling by boat, these early people could have hopscotched their way south of the ice sheets, subsisting on the rich marine resources of the ice-free strip along the shore.

The search for these sea-going settlers will not be easy. Much of the evidence that archaeologists seek is deep underwater — or was smashed long ago by the Pacific's legendary waves. But momentum is building to find those earliest settlers. “People are just more optimistic,” says Quentin Mackie, an archaeologist at the University of Victoria in Canada. Amanda Evans, a marine archaeologist at the ocean-survey company Tesla Offshore in Prairieville, Louisiana, says that prehistoric underwater archaeology in general is having a moment. “This year just seems to be the year that everybody was pushing the ball uphill and it finally crested.”

Tools of the trade

Loren Davis, an archaeologist at Oregon State University in Corvallis, is searching for the ancient seafarers in an unusual spot — at a site in Idaho called Cooper's Ferry, which is on a bank of the Salmon River, hundreds of kilometres away from the coast. At the dig site in August, Davis examines a piece of rock brought to him by one of his field crew. He turns it over to see whether it was shaped by human hands, perhaps by early toolmakers who littered the ground with flakes of rock as they worked.

Coopers ferry photoArchaeologists search for signs of early inhabitants near a riverbank at Cooper's Ferry, Idaho - Hayden Wilcox

Although Cooper's Ferry is far inland, Davis suggests that it is part of the coastal story. The Salmon is a tributary of the mighty Columbia River, which would have been the first large waterway encountered by people who made it south of the ice sheets during the last glacial epoch. At that time, valleys farther north would have been covered by glaciers. For a water-adapted culture, he says, “the first off-ramp south of the ice is the Columbia River”.

Having considered the stone, Davis hands it back to his colleague and says, “I think it is a flake.” His archaeological pits, which the crew has shaped into a series of neat holes, are full of flakes and finished 'western stemmed' points up to 13,200 years old1. Whereas the Clovis points are shaped like miniature surfboards, the western stemmed points from Cooper's Ferry are smaller and look like Christmas trees. Points resembling the western stemmed variety have been found throughout the western United States and in Siberia — a connection that suggests they were brought over to the New World by early hunters.

Davis's crew is quietly intent, and the air is filled with the gentle sound of trowels scraping earth, along with a rock wren's distinctive call. The peace is occasionally broken by shouts between diggers and data recorders: “Bone!”, “Fire-cracked rock!” or “Deb!” (short for debitage, or flakes). The position of each artefact is precisely recorded, then it is bagged up and stored in one of many boxes that are piling up in a nearby trailer. Precise dates will be assigned later, in the laboratory.

A sense of expectation hangs over the dig. If the team uncovers particularly old western stemmed points that definitively pre-date the Clovis era, that would strongly suggest that the first Americans carried these points there by sea and river. “You get a gambler's mentality,” Davis says. The hunt obsesses the crew, who spend weeks here, camped out and digging for hours each day. Sarah Skinner, an Oregon State student who supervises pit B, says that she wakes up clenching her fists around dream trowels. “When I close my eyes, I see artefacts,” she says.