New evidence from caves in Oregon may finally put to rest the long-held theory that the early people who made Clovis spear points were the first inhabitants of North America.
The new evidence indicates that a second group of people that made what are known as western stemmed projectile points arrived on the North American continent at least as early as those who made the Clovis points, and perhaps even earlier. The new finds provide strong support for growing genetic evidence that indicates the Americas were populated in at least three waves of immigration beginning at least 15,000 years ago.
"Our evidence puts the final blow to the Clovis First theory," said geneticist Eske Willerslev of the University of Copenhagen in Denmark. "Culturally, biologically and chronologically, the theory is no longer viable."
The accumulation of new data represents "almost a revolution in our understanding of the early colonization of the Americas," said Brooks Hanson, an editor at the journal Science, in which the newest data was published Thursday.
The distinctive fluted Clovis spear points were first discovered in 1932 at Blackwater Draw, near the village of Clovis, N.M. They have subsequently been found throughout the eastern and Southern United States, and artifacts associated with them have been dated to about 13,000 years ago.
It has long been held that the points were made by people who immigrated to North America from Asia across the Bering land bridge, a route connecting Siberia and Alaska exposed when ocean levels fell during the most recent ice age. A second, technologically distinct spear point known as the western stemmed projectile point has been found throughout much of the western United States, and Clovis proponents have argued that it was a descendant of the Clovis technology. The two types of spear points differ primarily in how they are attached to the shaft of the spear.
The first crack in the Clovis First theory came in 2008 when Willerslev, archaeologist Dennis L. Jenkins of the University of Oregon, and their colleagues reported they had found 14,300-year-old human coprolites in the Paisley Caves of Oregon. Coprolites are essentially desiccated human feces. The team found other artifacts with the coprolites, but no Clovis points.
Critics, however, argued the coprolites had been contaminated, perhaps by the excavators or by animals urinating at the site. The critics also argued the stratigraphy of the site may have been scrambled by rodents burrowing through the sediments. Essentially, they claimed, the results were bogus.
The Paisley Caves, originally discovered in 1938 by University of Oregon anthropologist Luther Cressman, are in the Summer Lake basin about 220 miles southeast of Eugene on the east side of the Cascade Range. The eight caves, which face to the west, are wave-cut shelters on the shoreline of Lake Chewaucan, whose levels have risen and fallen with climate change.
Angered by the criticism, Jenkins and his students have revisited the caves during each of the last three summers. They wore full body suits, face masks and gloves to prevent human contamination of samples -- even though they had analyzed DNA of all the archaeologists and lab workers involved with the earlier study to rule out contamination.
The team also drilled small core samples through several different regions of the caves, dating each layer of sediment to show the layers had not been jumbled. Organic samples destined for radiocarbon dating were soaked in distilled water to remove potential contaminants. The distilled water itself was also dated to determine when foreign materials might have been introduced. They also found western stemmed projectile points, but no Clovis points.
Their conclusions: the same as before. The human sample dating was accurate and the western stemmed projectiles were 12,800 to 13,000 years old -- at least as old as the oldest dated Clovis points.
"From our dating, it appears to be impossible to derive western stemmed points from a proto-Clovis tradition," Jenkins said. ""It suggests that we may have here in the western United States a tradition that is at least as old as Clovis, and quite possibly older. We seem to have two different traditions co-existing in the United States that did not blend for a period of hundreds of years."
The increasingly older ages of human habitation of the continent suggests at least some of the new immigrants could not have crossed the Bering land bridge -- it was covered with water when they came.
University of Oregon archaeologist Jon Erlandson has been accumulating evidence -- much of it from the Channel Islands off the California coast -- that some of the first immigrants might have been a seagoing people that migrated along the coast lines of Asia and North America, exploiting wildlife found in kelp beds along the coast. Many of their potential camp sites and shelters, however, would have been flooded by rising sea levels and are no longer accessible.
Intriguingly, stemmed projectiles that could be attached to spears originated in Asia about 4,000 to 5,000 years before the points in the Paisley Caves were created, but archaeologists have never found either Clovis points or western stemmed points on that continent. The lack of evidence thus suggests that the technology for making both was uniquely American.