How and when humans first entered the Americas has been hotly debated for centuries. The Beringian Land Bridge theory has been widely accepted since the 1930s. This model proposes that Paleo-Indians migrated from Siberia into Alaska overland, via the now-submerged landmass of Beringia, then on into North America by way of an interior passage (the Mackenzie Corridor) along the eastern flank of the Rocky Mountains.
The Pacific Coast Migration Model came to prominence in 1979 when archaeologist Knut Fladmark proposed another migration route into the Americas which followed the Pacific Rim from Asia, along the coastal edges of Beringia and down along the Alaskan and Canadian coast.
Geological evidence up to now suggested that, when the Laurentide and Cordilleran ice sheets were at their maximum extent, both routes were impassable between 23,000 and 15,000 years ago. The ice sheets covered hundreds of thousands of square miles of North America from coast to coast, and were up to 2 miles thick in places. Deep crevasses on their surface made travel across them potentially lethal. Glaciers hundreds of miles wide which flowed into the sea, and masses of icebergs, made travel by watercraft equally hazardous.
However, increasing archaeological evidence of coastal sites in South America, the earliest dating to around 15,000 years ago, has contradicted this accepted chronology. Around the time that Paleo-Indians were establishing a settlement at Monte Verde in southern Chile, the Pacific coast and Mackenzie Corridor routes thousands of miles to the north were supposedly just becoming free from the ice which had blocked off the whole continent to human migration.
Sanak Island lies around the midpoint of the Aleutian Archipelago extending off Alaska. It is 15 miles long by 6 miles wide and is capped by a single volcano called Sanak Peak. The Aleutians would have been the highest point on the Beringian landmass. The analysis of pollen from sagebrush, heather, willow and grasses, as well as radiocarbon-dated deep water sediments, from the bottom of 3 lakes on Sanak indicate that the island and its now-submerged coastal plains (and therefore the northern part of the Pacific coastal route) were free of ice by around 17,000 years ago.
This would have allowed a first wave of maritime-adapted Paleo-Indians from Beringia to move south down the coastal islands from Alaska by watercraft. Within 2,000 years their descendants could comfortably have reached as far south as the Chilean coast, just as their land-lubbing Beringian cousins were moving through the ice free Mackenzie Corridor in the north.
The evidence for this Pacific coastal migration remains largely circumstantial as any archaeological evidence that these seafaring Paleo-Indians may have left behind now lies under 160 feet of water. However, the findings on Sanak Island will certainly fuel this long-running debate.