Archaeologists at a Central Texas site have unearthed artifacts that the first humans arrived in North America roughly 2,500 years earlier than previously thought, raising questions about how they made it to the New World and what route they took to get here.

The artifacts found along a creek bed west of Salado by a Texas A&M University-led team date back as far as 15,500 years, more than 2,000 years before the Clovis people who were long believed to be the first humans in North America. The so-called Clovis people were named after a site found in 1930 near Clovis, N.M.

Known for their unique spearhead artifacts, the numerous Clovis artifacts were found over the last 80 years and showed they lived as far back as 13,100 years ago.

The Salado site isn’t the first find to challenge when humans migrated to the Americas — other sites have been found in Pennsylvania, Oregon and Chile — but it is the most complete with over 16,000 artifacts, said Michael Waters, director of the Center for the Study of the First Americans at Texas A&M University.

“”Now Texas can boast having the oldest (human) archaeological site in North America,”” Waters said. “”… This is the strongest evidence yet that humans colonized North America2,500 years earlier than we first thought.””

While other pre-Clovis locations have artifacts, they aren’t “”very robust.”” Waters said the latest discovery should win over most skeptics that humans occupied North America at an earlier date.

“”We have the … biggest assemblage of pre-Clovis material, the biggest variety of artifacts,”” Waters said.

Most of items would look like crude spears, knives, notches or other types of cutting or sharpening tools. But they indicate the area along a spring-fed creek was used as a campsite as they came and went from the area.

The archaeological evidence shows human occupation almost continuously for 15,000 years and signs that water was present even during times of drought. Recent historical records show the creek still had water during the severe droughts of the 1930s and 1950s.

The clay sediment helped preserve the artifacts and scientists used luminescence dating, a technique to date the sediment around the artifacts. It is done by dating the last time the sediment was exposed to sunlight.

Researchers “”had the right kind of sediment,”” said Lee Nordt, dean of the College of Arts and Sciences at Baylor University. “”Fortunately, it is very difficult to mix. The artifacts had a greater tendency to stay in place.””

Besides Baylor and Texas A&M, the work at the Central Texas site also included researchers from the University of Illinois-Chicago, the University of Minnesota and Texas State University. Their findings were released Thursday and are being published in the current issue of Science magazine.

Waters said the work at the Salado site adds to the evidence found at other pre-Clovis sites but that “”each site has to stand on its own and by its own merits.””

If humans arrived 2,500 years earlier in North America, it also raises the question of how they made their way to Texas.

Fifteen thousand years ago, the Canadian ice sheets would have blocked a land migration to North America, Waters said. That theory espoused by Waters and other archaeologists raises the possibility that humans traveled by boat along the West Coast of what is now Canada down to the Columbia River along the present-day Washington–Oregon border — or perhaps even farther south.

“”If you look at the genetic evidence, the native people in North America came from Northeast Asia, then crossed over into the New World, either coming across by the Bering land bridge or they could have skirted over by boat,”” Waters said. “”The corridor between the two ice sheets was closed 15,000 years ago. The only option to them is to come by boat in this kind of secondary way, along a coastal route to get into North America.””

Waters cautions that there is no empirical evidence to support it. Sea levels were lower 15,000 years ago, so any evidence would likely be buried under the ocean floor. But he notes that the oldest human skeletal remains in North America were found on the Channel Islands off the coast of California and are dated at 13,000 years old. Those islands were never part of the mainland so they would have been reached by boat and researchers are currently studying caves there for signs that humans could have been there 16,000 years ago.

For people to be living in Texas 15,500 years ago, it means they had to be in other parts of North America even earlier. The find underscores the need to search across other areas of North America for pre-Clovis sites. Besides the Channel Islands, researchers are currently combing the Columbia River for any evidence of humans that far back.

Over the next several decades, Waters expects the archaeological and DNA evidence to answer many of the unknowns.

“”What we’ve done here is create all sort of possibilities,”” Waters said, adding that researchers are no longer held back by “”the Clovis-first dogma.””

Yet there is much that isn’t known, like how early the first humans could have arrived in North America.

“”Yes, people were here earlier, but how much earlier?”” Waters said. “”That is the mystery. That is what we still need to know. Is it 16,000 or 24,000 years ago? Only time will tell.””