For over a decade now, archaeologists and geologists from around the world have been attempting to determine the origin of these stone spheres scattered throughout the globe, from Franz Joseph Land to New Zealand.4 photos

The largest number of stone spheres can be found in Costa Rica, where there are approximately 300 of them. The age of most of these spheres is estimated to be around 12,000 years. Scientists have discovered that while the majority are made from hard lava rock, some examples are also crafted from sedimentary rocks. These stones underwent thermal treatment—being repeatedly heated and cooled—to make their outer layers more malleable. Spheres similar to these have also been found in other countries in Central America, the United States, New Zealand, Romania, Kazakhstan, Brazil, and Russia. However, many of these spheres have been stolen, damaged, or destroyed. Treasure hunters once believed that gold might be hidden inside them, while scientists also speculate that in Central America, such spheres might have been displayed in front of the homes of wealthy individuals as a symbol of their status. It remains difficult to explain the purpose of these spheres in places like New Zealand or Franz Josef Land.