Mysterious metal spheres measuring about an inch in diameter have been found in South Africa in rock dated to 2.8 billion years old, and some are etched with three parallel grooves. Fossils that seem out of place have also been found, including a human handprint in limestone estimated at 110 million years old and a possible human footprint from 300-600 million years ago. In 1938 in China, an expedition discovered a cave containing hundreds of stone disks approximately nine inches in diameter with a central circle and spiral groove etched with tiny hieroglyphs telling a story about a crashed spacecraft and its pilots called the Dropa.