In Intelligent Life in the Universe (1966) astrophysicists Iosif Shklovsky [Shklovskii] and Carl Sagan devote a chapter to the argument that scientists and historians should seriously consider the possibility that extraterrestrial contact occurred during recorded history; however, Shklovskii and Sagan stressed that these ideas were speculative and unproven.
Shklovskii and Sagan argued that sub-lightspeed interstellar travel by extraterrestrial life was a certainty when considering technologies that were established or feasible in the late 1960s; that repeated instances of extraterrestrial visitation to Earth were plausible; and that pre-scientific narratives can offer a potentially reliable means of describing contact with aliens.

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.
 Over a century after its occurrence it was then recorded by anthropologist George T. Emmons.
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.
 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, Shklovskii 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.

In his 1979 book Broca's Brain, Sagan suggested that he and Shklovskii might have inspired the wave of 1970s ancient astronaut books, expressing disapproval of "von Däniken and other uncritical writers" who seemingly built on these ideas not as guarded speculations but as "valid evidence of extraterrestrial contact."
Sagan argued that while many legends, artifacts, and purported out-of-place artifacts were cited in support of ancient astronaut hypotheses, "very few require more than passing mention" and could be easily explained with more conventional hypotheses.
Sagan also reiterated his earlier conclusion that extraterrestrial visits to Earth were possible but unproven, and improbable.
In Intelligent Life in the Universe (1966) astrophysicists Iosif Shklovsky [Shklovskii] and Carl Sagan devote a chapter to the argument that scientists and historians should seriously consider the possibility that extraterrestrial contact occurred during recorded history; however, Shklovskii and Sagan stressed that these ideas were speculative and unproven. Shklovskii and Sagan argued that sub-lightspeed interstellar travel by extraterrestrial life was a certainty when considering technologies that were established or feasible in the late 1960s; that repeated instances of extraterrestrial visitation to Earth were plausible; and that pre-scientific narratives can offer a potentially reliable means of describing contact with aliens.
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.  Over a century after its occurrence it was then recorded by anthropologist George T. Emmons. 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.  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, Shklovskii 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.
In his 1979 book Broca's Brain, Sagan suggested that he and Shklovskii might have inspired the wave of 1970s ancient astronaut books, expressing disapproval of "von Däniken and other uncritical writers" who seemingly built on these ideas not as guarded speculations but as "valid evidence of extraterrestrial contact." Sagan argued that while many legends, artifacts, and purported out-of-place artifacts were cited in support of ancient astronaut hypotheses, "very few require more than passing mention" and could be easily explained with more conventional hypotheses. Sagan also reiterated his earlier conclusion that extraterrestrial visits to Earth were possible but unproven, and improbable.
Ancient astronauts