Ancient astronaut theories are various proposals that Earth has been visite by intelligent extraterrestrial beings, and that such contact is linked to either the origins or development of human cultures, technologies and/or religions. Some of these theories suggests that gods from most — if not all — religions are actually extraterrestrial beings, and their technologies were mistaken for divine entities by primitive man. While no peer-reviewed scientific journal validates such claims, these theories have been popularized, particularly in the latter half of the 20th century, by writers Erich von Däniken, Zecharia Sitchin and others.