However it happened, the first ever human migration through the Americas is sure to have been dramatic. After crossing the Bering Land Bridge between Siberia and North America, the earliest arrivals in the (old) New World would have been greeted by a hostile, icy landscape. Until recently, it had been assumed that these original American pioneers later worked their way south via a corridor that opened up between two retreating ice sheets, although new research suggests that this passage was actually completely uninhabitable at the time, and any attempt to traverse it would most likely have proved deadly.
According to previous radiocarbon dating studies, the Cordilleran and Laurentide ice sheets that once covered much of northern North America began to retreat several millennia ago, leading to the appearance of a 1,500-kilometer (930-mile) corridor between the two around 14-15,000 years ago. For a long time, archaeologists believed that the earliest settlers in the Americas were the Clovis people, who appeared to the south of these ice sheets around 13,400 years ago. Given these dates, it made sense to deduce that they had probably migrated south through this corridor.
The corridor between the Cordilleran and Laurentide ice sheets became traversable around 12,600 years ago, suggesting that the first migration southwards through the Americas may have followed a coastal route instead. Mikkel Winther Pedersen
More recently, however, new evidence has come to light indicating that people lived in the Americas around 14,700 years ago. While some debate exists as to who these mysterious early settlers were, their appearance also calls into question the classic tale of the first American migration, leading many to favor a new theory that the original Pan-American highway was not down the middle of two ice sheets, but along the Pacific coast.