During the last ice age , glaciers cover Brobdingnagian swathes of western North America . investigator have nominate that an ice - free corridor served as a pathway for human migration between the far north and the relief of the continent . Now , an analysis of bison fossils revealed that humans made their ice - free direction in and out of Alaska and the Yukon some 13,000 years ago . The determination are issue inProceedings of the National Academy of Sciencesthis week .
Our specie dispersed to the North American continent via an ancient nation bridgework that connected Siberia with Alaska , and from there , humans last on to colonize the rest of the Americas . In the seventies , geological studies proposed the creation of a homo ( and animate being ) migration itinerary through an ice - liberal corridor along the Rocky Mountains between large continental ice sheets toward the goal of the Pleistocene . The corridor in all probability open and close multiple time as the climate shift . We know , for example , that it was n’t open 21,000 old age ago at the height of the sparkler geezerhood because the ice sheets immix . Exactly when that corridor open for human migration remained unidentified .
To inquire , an outside squad led by University of Alberta ’s Duane Froese and Beth Shapiro from UC Santa Cruz reconstructed the corridor ’s chronology using carbon 14 go steady and mitochondrial DNA extracted from the fossilized teeth and bones of steppe bison ( Bison priscus ) . These giant mammals roamed freely throughout the grassland of North America until the ice plane cut off the bison in the north from those in the Confederate States of America . Over meter , they became genetically clear-cut .
The oldest bison fossils witness within the corridor neighborhood belong to to the derivation that spring up south of the icing sheets during a clip when the corridor was closed . The squad see these bison fossils to 13,400 age ago . " The carbon 14 dates told us how one-time the fossils were , but the key affair was the genic analysis , because that told us when bison from the northerly and southerly populations were able-bodied to meet within the corridor , " first author Peter Heintzman of UC Santa Cruz said in astatement . The southern part of the corridor open up up first , allow bison to move north . Later on , the northern population make a motion southward , and the two encounter in the corridor by around 13,000 twelvemonth ago . That means the corridor was undefendable – and fully traversable for humans – by this time .
However , archaeological evidence suggests that a southward migration out of Alaska and the Yukon occurred before 15,000 years ago – which we now know raven the corridor ’s opening . The research worker think the corridor was n’t used for this initial southbound dispersion – they likely took a Pacific coastal route . But the ice - loose corridor did enable subsequent movement , both northward and southward . The Clovis hound polish , for example , was widespread in the south some 13,000 yr ago . The earliest known Alaskan Clovis site date stamp back to 12,400 years ago .
