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.