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The first people who lived in North America arrived at least 14,000 years ago. They're largely a mystery. Archeologists haven't found much that tells us about their culture: hardly any weavings, pottery or other handiwork. But as NPR's Elizabeth Shogren reports, a new discovery shows that some of these early North Americans were surprisingly creative artists.

ELIZABETH SHOGREN, BYLINE: Ten years ago, Larry Benson got a chance to check out some rock art on an Indian reservation north of Reno. He was entranced.

DR. LARRY BENSON: Well, these things are incredibly beautiful. They're larger than most petroglyphs in the Southwest.

SHOGREN: He saw a heap of big boulders, nearly every surface covered with geometric patterns, things like concentric circles, groups of diamond shapes and tree-like symbols.

BENSON: And they're almost unique in the sense that the grooves have been carved down almost an inch deep in some cases.

SHOGREN: And just by looking at them, Benson thought he might know how old they were. He noticed that the symbols are much whiter than the gray rock they're carved into. Benson is a paleoclimatologist who works with the University of Colorado. He knew from his climate research that the dry area where the petroglyphs are located was once was a lake and that the white coating was probably left from the last time the rocks were submerged in water.

BENSON: So this would indicate that the petroglyphs were older than 11,000 years. And I did know, at least from my limited knowledge, that these were probably then the oldest dated petroglyphs in North America.

SHOGREN: But to prove it, he needed permission to take samples. That took years. Once he dated the different coatings on the rock, he confirmed that the artwork was at least 10,000 years old and maybe 15,000 years old. He published his findings in the journal of Archaeological Science.

BENSON: Well, I think it's really amazing that people that far back were creating such wonderful things.

SHOGREN: University of Oregon archeologist Dennis Jenkins dated the earliest known people in North America. He says it's nearly unheard of to find artwork of any kind as old as the Nevada petroglyphs.

DR. DENNIS JENKINS: To get something this complex this early is very, very rare.

SHOGREN: Jenkins says many other lakes in the West rose and fell thousands of years ago when the climate was making dramatic shifts. He's hoping that Benson's techniques for dating petroglyphs can be replicated elsewhere. That could help experts understand more about the people who lived on this continent long ago. Elizabeth Shogren, NPR News.

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