The scientists believe the tools were human-made, Mattson said, as opposed to having being chipped by glacial movements.
"We have trouble attributing this [chipping] to natural geological forces," he said.
"The pieces have been consistently worked . Combine that with the number of artifacts that we have in a confined area and it starts to look statistically at odds with a natural occurrence."
Most scientists believe the first humans entered North America from Asia via a land bridge to Alaska at least 15,000 years ago.
(Related news: "First Americans Arrived Recently, Settled Pacific Coast, DNA Study Says" [February 2, 2007].)
According to one theory, the first Americans initially spread into the continent along a coastal route.
The oldest human remains found in Minnesota date back to about 9,000 years ago and were discovered in 1933 near the western town of Browns Valley.
"If the [newly discovered] site does indeed prove to be 13,000 years old, it would indicate human movement into cooler latitudes during terminal Pleistocene times," said Tom Dillehay, chair of the anthropology department at Vanderbilt University.
The Pleistocene epoch lasted from 1.8 million years ago to 11,500 years ago. Shifting glaciers covered much of Minnesota at the time.
But some researchers have suggested that the north-central part of the state may have been something of an "oasis" 13,000 years ago—an area free of ice cover, with an access route to the southeast.
"The best glacial models that we have now indicate that the central part of Minnesota might have been viable for human occupation earlier than some of the rest of it," Minnesota-based archaeologist Mattson said.
"There are certainly things to be learned about the habitability of certain areas of Minnesota, which would open up the potential for more thorough testing of other similar or viable landforms related to a period of time that is not well understood," Mattson added.
The archaeologists hope that the Minnesota site, which lies in the path of a major city development project, can be preserved and further excavated.
The team also wants to use a geologic dating technique known as optically stimulated luminescence (OSL) to more directly determine the age of the objects.
Meltzer, the Southern Methodist University archaeologist, said he will reserve judgment until the objects have been dated and more is known about them.
"One hates to rain on the parade," he said, "but we've been down this road before—claims of great antiquity that fizzle—and have learned the hard way to be wary."
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