Workmen hacking and burning their way through the dense jungle of Costa Rica to clear an area for banana plantations in the 1930s stumbled upon some incredible objects: dozens of stone balls , many of which were perfectly spherical. They varied in size from as small as a tennis ball to an astonishing 8 feet in diameter and weighing 16 tons! Although the great stone balls are clearly man-made, it is unknown who made them, for what purpose and, most puzzling, how they achieved such spherical precision.

While mineral hunting in the mountains of California near Olancha during the winter of 1961, Wallace Lane, Virginia Maxey and Mike Mikesell found a rock, among many others, that they thought was a geode - a good addition for their gem shop. Upon cutting it open, however, Mikesell found an object inside that seemed to be made of white porcelain. In the center was a shaft of shiny metal. Experts estimated that, if this was a geode, it should have taken about 500,000 years for this fossil-encrusted nodule to form, yet the object inside was obviously of sophisticated human manufacture. Further investigation revealed that the porcelain was surround by a hexagonal casing, and an x-ray revealed a tiny spring at one end, like a spark plug. There's a bit of controversy around this artifact, as you can imagine. Some contend that the artifact was not inside a geode at all, but encased in hardened clay. The artifact itself has been identified by experts as a 1920s-era Champion spark plug. Unfortunately, the Coso Artifact has gone missing and cannot be thoroughly examined. Is there a natural explanation for it? Or was it found, as the discoverer claimed, inside a geode? If so, how could a 1920s sparkplug get inside a 500,000-year-old rock?