Historians used to believe that the first people on this continent came via a Bering Strait land bridge that connected Alaska to Siberia sometime during the last ice age -- 17,000 to 11,000 years ago, said historian Nicholas Vrooman.

But new evidence is calling this into question. Some historians suggest the first people came to this continent by both land and sea.

European prehistoric artifacts similar to ones in North America, such as Clovis points, have led some scholars to suggest that European prehistoric people crossed the Atlantic Ocean in boats, said Vrooman.

And research in Siberia, where the Bering land bridge supposedly originated, reveals no solid evidence of Clovis points originating there, he said.

Some archaeological sites in the Americas predate the land bridge.

A site in Brazil yields possible evidence of human habitation 37,000 years ago, long before the land bridge is believed to have existed, said Vrooman.

However, there are also historians who contend that the land bridge and travel corridor opened and closed over thousands of years during different ice age periods.

Helena Forest archaeologist Carl Davis said it's also likely that early people walked down the frozen coast from Alaska to Baja thousands of years ago.

"I think the Pacific coastline route was a viable route because much of the ocean water was locked up in huge continental ice sheets, leaving vast tracts of shoreline exposed, as well as an ice-free corridor coming down from the Yukon," Davis said.

"Unfortunately any archaeological evidence of this migration has long since disappeared under hundreds of feet of water," he said.

It's also possible that later migrants crossed the Pacific and arrived on the coast of South America, he said.