"The earliest reports of the stones come from the late 19th century, but they weren't really reported scientifically until the 1930s -- so they're a relatively recent discovery," Hoopes said. "They remained unknown until the United Fruit Company began clearing land for banana plantations in southern Costa Rica."
According to Hoopes, around 300 balls are known to exist, with the largest weighing 16 tons and measuring eight feet in diameter. Many of these are clustered in Costa Rica's Diquis Delta region. Some remain pristine in the original places of discovery, but many others have been relocated or damaged due to erosion, fires and vandalism.
The KU researcher said that scientists believe the stones were first created around 600 A.D., with most dating to after 1,000 A.D. but before the Spanish conquest.
Hoopes says the stones are definitely man made, despite legends linking them to Atlantis or space aliens, but scientists don't know why they were created. Link -via Digg