The latest research by scientists in the United States and Britain has found that the first humans to enter the Americas arrived by sea, not through the Bering Land Bridge, because 13,800 years ago, where the Bering Land Bridge was located, stood a huge ice wall up to 3,000 feet (about 914 meters), and the first humans who entered the Americas 26,500 years ago had to arrive from the sea.
The team examined exactly when the corridor that runs north-south through the land bridge corridor was fully opened.
For a long time, there have long been two theories about the way humans first migrated to North America, one is through the corridor known as the "Bering Land Bridge" that once connected Asia and North America, and the other is traveling along the Pacific coast from Asia by small water transport vehicles.
But whether the ancient humans entered North America by land depended on whether the Bering Land Bridge really existed in an ice-free corridor that allowed them to descend to the Great Plains.
The 60 footprints and stone artifacts discovered by scientists suggest that the first humans reached what is now the U.S. state of New Mexico about 23,000 years ago, and central Mexico before 26,500 years ago.
To find out whether they came by land or sea, a team at Oregon State University set out to determine when the ice-free corridor was opened.
Before 13,800 years ago, the land bridge passage was located with a huge ice wall, and ancient humans could only enter North America from the sea.
They found that the corridor was not fully opened until about 13,800 years ago, and that the corridor was located where it had previously stood up to 3,000 feet of ice, meaning the first ancient humans had to reach from the sea.
The study, the latest in a series of studies, does not support the long-standing "Clovis first" theory that the Clovis first arrived in the Americas from Siberia along an inland ice-free corridor formed during the last post-ice age.
The research team, led by Professor Jorie Clark of Oregon State University, said there was strong evidence that the ice-free corridor was not open to the first immigrants in the Americas, but was unavailable.
The team used the "cosmic nuclide exposure time" method to measure the time when rocks on the land bridge channel were exposed to the surface, and confirmed that the ice-free corridor did not open normally until 13,800 years ago.
To determine the exact opening hours of the ice-free corridor, the team examined 64 geological samples from 6 sites, spanning 745 miles, an area where the ice-free corridor is thought to exist.
The team looked at how long the rocks in these places were exposed to the surface, i.e., how long the rocks stayed on the ground without ice cover.
Dr Louise Guillaume, a team member from Imperial College London in the United Kingdom, said the team used a method known as "cosmic nuclide exposure time" to determine that the ice-free corridor did not open normally until 13,800 years ago, after a huge wall of ice blocked the corridor's entrance.
Study co-author Dr Dylan Rood from Imperial College London said the study clearly showed that the corridor could not have been used as a migration route as early as about 26,000 years ago when humans first entered the Americas, and that the "Clovis First" theory was self-defeating.
Text/Nandu reporter Chen Lin