Ancient Astronaut Theorists believe that past evidence of ancient civilizations may have been destroyed. See more in this clip from Season 15, "The World Before Time."

Watch all new episodes of Ancient Aliens, Fridays at 8/7c, and next day on The HISTORY Channel website at history.com/schedule.

#AncientAliens

Subscribe for more from Ancient Aliens and other great The HISTORY Channel shows:
histv.co/SubscribeHistoryYT

Find out more about the show and watch full episodes on our site:
histv.co/AncientAliens

Check out exclusive The HISTORY Channel content:
History Newsletter - histv.co/newsletter
Website - histv.co/History
Facebook - histv.co/Facebook
Twitter - histv.co/Twitter

"Ancient Aliens" explores the controversial theory that extraterrestrials have visited Earth for millions of years.

HISTORY® is the leading destination for award-winning original series and specials that connect viewers with history in an informative, immersive, and entertaining manner across all platforms. The network’s all-original programming slate features a roster of hit series, premium documentaries, and scripted event programming.

• Ancient Aliens: Biblical Evidence of Lost Pre-Historic Civilization (Season 15) ( Download)
• Ancient Aliens: Mars Rover Captures Evidence of Lost Civilization! (Special) ( Download)
• Ancient Aliens: Lost Race of Biblical Giants Uncovered (Season 16) | History ( Download)
• Ancient Aliens: Hieroglyphics Discovery Alters Timeline of Human History (Season 15) ( Download)
• Ancient Aliens: Dead Sea Scrolls Reveal Noah's True Origins (Season 16) | History ( Download)
• Ancient Aliens: Biblical Proof of Alien Contact (Season 17) ( Download)
• Ancient Aliens: Mind-Boggling Extraterrestrial Links EXPOSED in India ( Download)
• Ancient Aliens: Mysterious Engineering of Nan Madol (Season 15) ( Download)
• Ancient Aliens: Otherworldly Structure Found on Nan Madol (Season 15) ( Download)
• Ancient Aliens: The Bible's Shocking Connection to the Number 12 (Season 16) | History ( Download)
• Ancient Aliens: TERRIFYING GIANT CREATURES LIVED ON EARTH! ( Download)
• Ancient Aliens: Da Vinci's MIND-BLOWING Secrets Revealed ( Download)
• Ancient Aliens: The Mighty Shiva (Season 11, Episode 15) | History ( Download)
• Ancient Aliens: Civilization Buried Under Antarctica's Ice! (S14, E1) | Full Episode ( Download)
• Ancient Aliens: HIDDEN ALIEN CODE IN DNA UNCOVERED (Season 13) | History ( Download)