New evidence supports/denies the "Solutrean hypothesis"

The Solutrean hypothesis:

The Solutrean hypothesis is a controversial proposal that peoples from Europe may have been among the earliest settlers in the Americas, as evidenced by similarities in stone tool technology of the Solutrean culture from prehistoric Europe to that of the later Clovis tool-making culture found in the Americas. It was first proposed in 1998. Its key proponents include Dennis Stanford, of the Smithsonian Institution, and Bruce Bradley, of the University of Exeter.

In this hypothesis, people associated with the Solutrean culture migrated from Ice Age Europe to North America, bringing their methods of making stone tools with them and providing the basis for later Clovis technology found throughout North America. The hypothesis rests upon particular similarities in Solutrean and Clovis technology that have no known counterparts in Eastern Asia, Siberia or Beringia, areas from which or through which early Americans are known to have migrated.

Today the Washington Post and The Independent have articles about new findings on the Atlantic coast of North America that support the Solutrean hypothesis.

At the core of Stanford’s case are stone tools recovered from five mid-Atlantic sites. Two sites lie on Chesapeake Bay islands, suggesting that the Solutreans settled Delmarva early on. Smithsonian research associate Darrin Lowery found blades, anvils and other tools found stuck in soil at least 20,000 years old [note only the soil can be reliably dated, not the artifacts themselves]...
Further, the Eastern Shore blades strongly resemble those found at dozens of Solutrean sites from the Stone Age in Spain and France, Stanford says. “We can match each one of 18 styles up to the sites in Europe.”..
Stone tools recovered from two other mid-Atlantic sites — Cactus Hills, Va., 45 miles south of Richmond, and Meadowcroft Rockshelter, in southern Pennsylvania — date to at least 16,000 years ago. Those tools, too, strongly resemble blades found in Europe...
“The reason people don’t like the Solutrean idea is the ocean,” he said. No Solutrean boats have been found. But given that people arrived in Australia some 60,000 years ago — and they didn’t walk there — wood-frame and seal-skin boats were clearly possible, Stanford argues... 

One major problem facing investigators is that early peoples would have lived on the coast next to the ocean - but sea levels have risen so far since that time that the original coast is perhaps 50 miles off the current shoreline and deep underwater.  Caves and artifacts from those locations are difficult to find.

Addendum:   We've updated this post (originally published in 2012) to add some items We've recently encountered - first, from Germany's Der Spiegel, reporting on DNA studies of North Americans:

Now a team of scientists led by the Danish geneticist Eske Willerslev has analyzed the boy's [Clovis-era, found in Montana] origins and discovered that he descends from a Siberian tribe with roots tracing back to Europe. Some of the boy's ancestors are likely even to have lived in present-day Germany.
Their findings go even further: More than 80 percent of all native peoples in the Americas -- from the Alaska's Aleuts to the Maya of Yucatan to the Aymaras along the Andes -- are descended from Montana boy's lineage.
Last week, the scientists published the results of sequencing the child's DNA in the scientific journal Nature. Late last year, the same team published the decoded genome of another early human: A juvenile buried near Lake Baikal in Siberia some 24,000 years ago. Their genomes showed surprising ancestral similarities.

This earned Willerslev's team an astounding publishing achievement in just 100 days: The decoding of the genomes of the oldest analyzed members of homo sapiens in both the Old and the New Worlds. This has allowed them to reconstruct the settlement of the Americas via the Beringia land bridge during the ice ages -- when what is now the Bering Strait between Russia and Alaska was frozen over -- in greater detail than ever before.

That report is discussed in a Reddit thread and summarized on the Wikipedia page, and at USA Today:

When researchers analyzed the Anzick child's DNA and compared it to the genomes of living Native Americans, they found that the boy's family members were the ancestors of multiple Central and South American groups, such as the Maya of Central America and the Karitiana people of Brazil. Willerslev estimates that roughly 80% of Native Americans are descended from the Anzick group, contradicting claims by other scholars that the Clovis people didn't leave much of a genetic legacy...
The results overturn the idea that migrants who colonized the Americas after the Clovis people are the true ancestors to Native Americans. And the discovery "puts the final nail in the coffin" for the idea that the ancestors of Native Americans may have crossed to the New World from Europe, says study author Ripan Malhi of the University of Illinois at Urbana-Champaign.
With the genetic data, the researchers can construct a rough narrative of the peopling of the New World. From Siberia, ancient people gradually crossed a now-vanished land bridge to Alaska. Some drifted south, giving rise to the Clovis people and colonizing the United States and Central and South America. Others stayed in the north and founded the lineage leading to the modern-day Cree and Athabascan peoples of northern North America. The study is published in this week's Nature.

We have accordingly inserted "/denies" after "supports" in the post's title.

Addendum:  Reposted again, in part because this post has become one of the most-commented posts  and we'd like to have the current generation of readers be aware of it.  Mostly we wanted to add this information from a recent comment:

Just returned from a visit with Dr. Al Goodyear and his folks at "The Topper Site" in South Carolina. Documented, dated by the best available science, Pre-Clovis artifacts found at a Chert quarry have been robustly tested and are found to be 50,000 years old +. In fact, charcoal remnants so old that Radio Carbon dating is impossible found in the same layer have proven the case for human occupation at the site . It is ,in fact, a tool manufacturing site of the first magnitude, It is located on the banks of the Savannah River in S.C.. It is interesting to note that more Clovis and Pre-Clovis artifacts have now been found of the East coast of the U.S.A.than all of the rest of the country. I know not what this means, but it definitely means something. Dr. Goodyear will publish a definitive paper very soon, but his find (The Topper Site) has been visited and observed by many national and international academe professionals and many of the artifacts examined in situ and in the lab.

We'll have to await that "definitive paper" for details; I suspect it will encounter substantial resistance during the peer-review process.  The Wikipedia entry offers the standard counterarguments:

Goodyear, who began excavating the Topper site in the 1980s, believes that lithic objects at that level are rudimentary stone tools (and thus "artifacts"). Other archaeologists dispute this conclusion, suggesting that the objects are natural and not human-made. Other archaeologists also have challenged the radiocarbon dating of the carbonized remains at Topper...

A recent article on the Topper site was posted in Charleston's Post and Courier.

"Unifacial flake tools found at the top of the soil layer holding artifacts said to be 50,000 years old."