Other followers noted this and protested that Tsoukalos' claims were "not science" because they were not falsifiable or repeatable. Tsoukalos' idea of "repeatable" shows his ignorance of the idea. In archaeology, it would involve finding the same type of artifact in similar contexts. Instead, Tsoukalos believes "repeatability" refers to "doing the same thing again and again." In his mind, taking the small gold pre-Columbian jewelry vaguely shaped like airplanes, altering models of them to make them of different material and add a propulsion system not in the original, and then claiming they are "really" alien airplanes is "repeatability" because the "experiment" always comes out the same way when you make the same alterations according to a set of assumptions. (I don't really have a problem with imagining that the Inca invented small toy gliders; it really isn't that much more sophisticated than a paper airplane. The problem comes in imagining these were based on full-sized, functional aircraft with fuel and propulsion systems.)
To a question on whether ancient astronaut claims have been presented in peer-reviewed journals, he responds:
I challenge Tsoukalos to present any peer-reviewed journal articles from modern times (say, the past 20 years) in the fields of archaeology, anthropology, astronomy, the physical sciences, religious history, Classics, or related disciplines that positively support the ancient astronaut theory and utilize it in explaining material.
Tsoukalos promises to "tear to shreds" anyone who dares challenge him. I guess we'll have some fun this fall when I'm scheduled to appear on National Geographic Channel to do just that.