Ancient Aliens is counting down the top ten mysteries of the deep, from sunken continents to puzzling ruins on the ocean floor and even artifacts that might be remnants of Atlantis. Could these underwater mysteries provide a record of extraterrestrial visitation?

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The Human Experiment

Ancient Aliens explores the controversial theory that extraterrestrials have visited Earth for millions of years. From the age of the dinosaurs to ancient Egypt, from early cave drawings to continued mass sightings in the US, each episode in this hit HISTORY series gives historic depth to the questions, speculations, provocative controversies, first-hand accounts and grounded theories surrounding this age-old debate. Did intelligent beings from outer space visit Earth thousands of years ago?