What if life on Earth began in outer space? Are monuments like Stonehenge and Easter Island the last remains of an ancient alien visitation? This special investigates a theory some believe cannot be true, but many agree cannot be ignored.
If ancient aliens visited Earth, did they leave behind clues such as sophisticated aircraft, complex electrical grids and construction machinery? Are these examples of modern technology, or is there evidence that they existed thousands of years ago?
If ancient aliens visited Earth, who were they, and where did they come from? Possible historic evidence and beliefs from around the world are examined, from the Dogon people of West Africa to the Hopi and Zuni of North America.
If ancient aliens visited Earth, what was their mission? From crop circles to Egyptian hieroglyphics, evidence may exist in multiple cultures throughout history suggesting that aliens came here to explore, excavate raw materials and more.
Reports of encounters with strange beings and sightings of mysterious objects in the sky have occurred throughout history. Could these sightings, coming from every part of the world, be evidence that aliens have been with us all along?