Spearheads uncovered in an apple orchard here and a human skull fragment found in Kansas date back more than 10,000 years and could be evidence of the first humans to walk the continent, scientists say.

Two workers installing underground sprinklers at R&R Orchards last May stumbled upon stone spear points that could be 11,000 years old, said C. Vance Haynes, a University of Arizona professor of anthropology and geology."This is probably one of the most exciting finds that's occurred in many, many decades," Haynes said Tuesday. "There is a possibility these were the first people into the New World."

Artifacts uncovered so far in this central Washington town include stone tools, projectile points and bone implements. No human remains have been found since formal excavation began Monday, scientists say.

However, a human skull fragment discovered in Kansas was recently shown by new dating techniques to be about 15,400 years old, reported Larry Martin, a systematics and ecology professor at the University of Kansas.

The skull fragment, found in 1975, was dated using electron spin resonance, which involves measuring the density of trapped electrons that accumulate in bone as a result of environmental radiation after the material is buried.

The fragment likely "has a real shot at being one of the oldest Americans," Martin, curator of the university's Museum of Natural History, said last week.

Haynes, however, said resonance is a "much newer and less tried" method than the Carbon-14 dating usually used in dating archaeological discoveries. He said he was unaware of the Kansas discovery and was reluctant to compare the two finds.

The Washington artifacts have not been scientifically dated, say archaeologists on the excavation team, which includes representatives of Washington State University, the University of Wyoming and the Smithsonian Institution.

The orchard workers initially unearthed about 20 stone pieces, and an additional seven were found by archaeologists on Monday. Many are so-called Clovis points, named after a New Mexico site where such stone tools were initially discovered in the 1920s and 1930s.

The points would have been used on the end of spears to stab mammals like elephants, horses and bison, said Peter Mehringer of Washington State and director of the excavation project.

He, too, contended the find indicates people at least as old as any previously discovered in North America, although finds on other continents may be as old as 40,000 years.

"Clovis is the oldest (North American) culture for which we have duplicated evidence," Haynes said. Archaeologists on the scene said all previous Clovis finds have been scientifically dated to about 11,000 years ago.