You probably remember the Bering Land Bridge theory from history class: North America's first inhabitants traveled along a land bridge between Siberia and Alaska and discovered an immense new world less than 15,000 years ago. Just like the land bridge did 10,000 years ago, that belief now appears to be sinking. New research in the journal Nature suggests the land bridge was inhospitable until 12,600 years ago—some 900 years after the Clovis people were living in North America and 2,000 years after the earliest humans appeared in South America, report the Guardian and Los Angeles Times. This lends credence to the idea that the continent's first inhabitants actually arrived via boat or by traveling unknown routes along the Pacific shore.
Researchers who studied ancient plant and animal DNA from sites in Canada say a 930-mile land bridge existed by 13,000 years ago, but there was no vegetation—let alone any bison, mammoth, or rabbits—to sustain humans trekking across it until 12,600 years ago; a separate study published in June found bison on either side of the land bridge didn't mix until 13,000 years ago, reports Christian Science Monitor. "That means the first people entering what is now the US, Central and South America must have taken a different route," a researcher says. Scientists have yet to find evidence of boats or other travel routes along the Pacific shore, but as one scientist notes, because of the rise in ocean levels, "the majority of the archaeology is now underwater." (This study also knocks the land bridge theory.)