The oldest rock art in North America exists on limestone boulders at Nevada's now-dry Winnemucca Lake, a new analysis suggests. The petroglyphs, which include carvings of trees, leaves, and abstract designs, are likely between 10,500 and 14,800 years old, LiveScience reports. Scientists found the age by determining when the boulders were above the water line; there was a time when the lake was so full that the rocks, which are at an elevation of 3,960 feet, would have been submerged, UPI reports.
They did this by using radiocarbon tests, which revealed the age of the carbonate left on the rocks by the lake. They also analyzed sediment core nearby, and ultimately found the rocks were probably first exposed to air between 14,800 and 13,200 years ago, then again between 11,300 and 10,500 years ago. Previously, the oldest petroglyphs in North America were thought to be carvings at Long Lake, Oregon, that are believed to be at least 6,700 years old. As for what the Winnemucca rock art symbols mean, "We have no idea," says a researcher. (Read more petroglyphs stories.)