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They are hardly a new discovery, nor are they especially mysterious.In fact, archaeological excavations undertaken at sites with stone balls in the 1950s found them to be associated with pottery and other materials typical of the Pre-Columbian cultures of southern Costa Rica.They were transported, primarily by rail, all over Costa Rica. There are two balls on display to the public in the U. One is in the museum of the National Geographic Society in Washington, D. The other is in a courtyard near the Peabody Museum of Archaeology and Ethnography, at Harvard University in Cambridge, Massachusetts.
These objects are not natural in origin, unlike the stone balls in Jalisco, Mexico that were described in a 1965 National Geographic article.The balls were most likely made by reducing round boulders to a spherical shape through a combination of controlled fracture, pecking, and grinding.The granodiorite from which they are made has been shown to exfoliate in layers when subjected to rapid changes in temperature.Finally, they were ground and polished to a high luster.This process, which was similar to that used for making polished stone axes, elaborate carved metates, and stone statues, was accomplished without the help of metal tools, laser beams, or alien life forms.