Fieldwork revises ice-free corridor hypothesis of human migration

This series of maps shows the generalized glacial extent in North America as the Cordilleran and Laurentide ice sheets waxed and waned. From top to bottom, the maps show ice extent at about 25,000 years ago, 20,000 years ago, 14,500 years ago and 12,000 years ago. Credit: basemap by NOAA NGDC; modified by Kathleen Cantner, AGI.

The existence of an ice-free corridor through Canada during the climax of last glaciation, which allowed the first Americans to cross the Bering land bridge from Siberia and move south (about 13,000 years ago), has long been postulated in North American archaeology. Now, research based on the exposure ages of glacial rocks found in the corridor suggests a puzzling conclusion — that the open pathway closed several thousand years prior to 20,000 years ago and didn’t open again until between 13,000 and 12,000 years ago, well after the first Americans were in the Americas.

The findings, presented at last year’s Paleoamerican Odyssey conference, along with other recent findings, may leave researchers back “at square one,” with no conclusive evidence of when or how the first people arrived in North America, says Lionel Jackson, a geologist at Simon Fraser University in British Columbia and a co-author of one of the studies presented at the meeting. [...] http://earthmagazine.org