The Klerksdorp Spheres, from South Africa, dated 2.8 billion years ago

OOPARTS is an acronym for out of place artefacts, a term first coined by Ivan Sanderson to denote manufactured objects found in solid, undisturbed rock strata, just as fossilized animals and planets are found. Such objects are considered by some researchers as evidence of visitation to this planet by technologically-advanced extraterrestrials during ancient times. Reportedly, steel nails, gold threads, a metallic bell-shaped vessel, a gold chain and other unidentified artificial objects have been found in rock and coal beds millions and hundreds of millions of years old.