The earliest immigrants to North America came from Asia by walking across a land bridge between Siberia and Alaska approximately 15,000 years ago when sea levels were significantly lower, according to the commonly accepted theory.
However, a new hypothesis pushes back the colonization of North America to 22,000 years ago with European settlers, a notion some archaeologists disagree with.
The Solutrean hypothesis suggests that early Europeans were the first immigrants to the Americas based on distinct similarities in the European Solutrean tool-making style 17,000 to 22,000 years ago and the American Clovis tool-making style, which existed approximately 13,000 years ago.
Researchers found weapons that shared characteristics between American-style Clovis weapons and European-style Solutrean weapons in the U.S. East Coast.
In 1970, Virginia fishermen found a mastodon tusk and a sharp eight-inch stone blade in their net.
Dennis Stanford, an anthropologist at the Smithsonian Institution, dated the mastodon tusk to more than 21,000 years ago - several thousand years before Asian immigrants are thought to have arrived - meaning the blade was likely that old as well. Stanford proposed the Solutrean theory in 1999.
Stanford concluded that since the blade was not smoothed out by ocean currents, it must have been buried there. At the end of the last ice age the spot where the archeologists found the blade would not have been underwater.
My guess is the blade was used to butcher the mastodon, Stanford told The Washington Post. I'm almost positive.
Stanford and his partner, Bruce Bradley, presented their evidence in a new book, Across Atlantic Ice, which is starting to turn some heads.
I drank the Solutrean Kool-Aid, Steve Black, an archaeologist at Texas State University in San Marcos, told The Washington Post. I had been very dubious. It's something a lot of [archaeologists] have dismissed out of hand. But I came away from the book feeling like it's an extremely credible idea that needs to be taken seriously.
Among the claimed evidence is a buried anvil discovered by Stanford's research assistant Darrin Lowery in Maryland. Lowery dated the soil holding the anvil to at least 21,000 years ago. Lowery also found stone tools in a tiny museum in Virginia that were very similar to the Soultrean style.
Not much is known about the Solutrean people who lived in what is now Spain, Portugal and France approximately 25,000 years ago. Stanford contends Solutrean rock art depicts a deep-sea halibut and seal with an arrow through it, evidence that the Solutreans had boats that they could have used to migrate to America.
Stanford has had a hard time convincing skeptics of his theory.
I'm not going to hang a completely novel interpretation of the peopling of the Americas from something dredged off the sea bottom 40 years ago and not properly documented, David Meltzer, an archaeologist at Southern Methodist University, told The Washington Post.
If Solutrean boat people washed up on our shores, they suffered cultural amnesia, genetic amnesia, dental amnesia, linguistic amnesia and skeletal amnesia, he said. Basically, all of the signals are pointing to Asia as where Americans originally came from, he said.
Critics add that Stanford has not yet proven that either the blades or the anvil, though very similar to Solutrean style, came from the earlier time period. The evidence came from a mastodon tusk found near the blade and dating the soil underneath the anvil.
Stanford knows he doesn't have all the answers yet - he's called the idea skeletal. He is planning a trip to the original Cinmar site, where he will look for more clues to support his hypothesis.
The Solutrean hypothesis isn't the only alternative theory of how humans came to the Americas. Costal migration theorists agree that the first people likely came from Asia, but not over a land bridge into Alaska.
Instead, the theorists say the early immigrants came by boat and followed the Pacific coast. This would explain how early settlers moved as far south as Chile and Venezuela in a short period of time, something the land bridge theory fails to do.