The evidence is argued to include archaeological artifacts that they deem anachronistic, or beyond the accepted technical capabilities of the historical cultures with which they are associated.These are sometimes referred to as "out-of-place artifacts"; and include artwork and legends which are interpreted in a modern sense as depicting extraterrestrial contact or technologies.Sagan illustrates this hypothesis by citing the 1786 expedition of French explorer Jean-François de Galaup, comte de La Pérouse, which made the earliest first contact between European and Tlingit cultures.The contact story was preserved as an oral tradition by the preliterate Tlingit.He further states that the reconstruction will be greatly aided if 1) the account is committed to written record soon after the event; 2) a major change is effected in the contacted society; and 3) no attempt is made by the contacting civilization to disguise its exogenous nature." Additionally, Shklovski and Sagan cited tales of Oannes, a fishlike being attributed with teaching agriculture, mathematics, and the arts to early Sumerians, as deserving closer scrutiny as a possible instance of paleocontact due to its consistency and detail.
The origins of many religions are interpreted by von Däniken as reactions to encounters with an alien race.Over a century after its occurrence it was then recorded by anthropologist George T. Although it is framed in a Tlingit cultural and spiritual paradigm, the story remained an accurate telling of the 1786 encounter.According to Sagan, this proved how "under certain circumstances, a brief contact with an alien civilization will be recorded in a re-constructible manner.Scholars have responded that gaps in contemporary knowledge are not evidence of the existence of ancient astronauts, and that advocates have not provided any convincing anecdotal or physical evidence of an artifact that might conceivably be the product of ETI contact.
According to astrophysicist Carl Sagan, "In the long litany of 'ancient astronaut' pop archaeology, the cases of apparent interest have perfectly reasonable alternative explanations, or have been misreported, or are simple prevarications, hoaxes and distortions".
He hypothesizes that the gods of old Mesopotamia were astronauts from the planet "Nibiru", which Sitchin states the Sumerians believed to be a remote "12th planet" (counting the Sun, Moon, and Pluto as planets) associated with the god Marduk.