For years, South African miners have been finding disks and spheres like this one. Usually brown or red, the objects can measure up to 10 centimeters in diameter, and like this one they’re often engraved with parallel grooves or ridges.

How could worked artifacts have found their way into mineral deposits that are billions of years old? Did aliens visit southern Africa in the remote past? Or is the region’s geologic history vastly different than we’d imagined?

Neither. Despite their artificial appearance, geologists say the objects arose naturally, probably as concretions as volcanic sediments in the region hardened into pyrophyllite.

See The Eltanin Antenna.