PASADENA, Calif. -- It was barely two hours into Day 1 of AlienCon and 500 years of accepted history and science were already being tossed out. Three thousand people had gathered inside the Civic Auditorium here for a panel discussion featuring presenters from ''Ancient Aliens,'' a History Channel documentary series.

Everyone had questions: about whether we were alone in the universe; about what our government really knows; about humanity's very origins.

One of the network's most popular and longest-running shows (Season 13 resumed on July 20), ''Ancient Aliens'' is itself a series of questions. Many are posed rhetorically by an unseen narrator intoning over a wide shot of a rubbly archaeological site. According to the show's talking heads, extraterrestrials may have had a role not only in the extermination of the dinosaurs, but also in the construction of the Egyptian pyramids.

Carl Sagan, the popular scientist who captivated television audiences of the 1970s and '80s, once said: ''Extraordinary claims require extraordinary evidence.''

But Mr. Sagan has been dead for years, and many Americans of the internet age have been in a mood to challenge established ideas. There has been a resurgence of the flat-earth theory. More than a few believe that global warming is a hoax, that survivors of mass shootings are crisis actors.

Yet for many at the conference, and elsewhere, this is not simply a political divide. We now know that the history that had been taught for years excluded the experiences of so many (African-Americans, women, the working poor). What else had been left out? Trust in the government and leaders who could set it all straight is historically low.

And there are so many people ready to believe that aliens visited Earth before recorded history that some 10,000 attendees paid to visit this conference over three days.

In the audience was Chris Bayley, a neatly dressed lawyer who had traveled from Arizona with his two adult sons. ''Just because someone says the Egyptians made the temples with ropes and wooden rollers doesn't make it true,'' Mr. Bayley said. ''We shouldn't accept blindly things we've been taught by quote-unquote scientists.''

Earlier that morning, a woman had risen from the crowd and told the ''Ancient Aliens'' producers: ''I'm indoctrinating my children in your show so they'll ask questions and not believe everything they're told.''

During the question-and-answer period, a wheelchair-bound man of about 60 was handed a microphone. He asked, ''Do you believe we are indigenous to this planet?''

It was Giorgio who answered him, naturally: Giorgio A. Tsoukalos, 44, the show's breakout star, the one they'd most come to see and get their picture with. He was dressed as he would be all weekend, in the khaki shirt and pants and sturdy leather boots of a field archaeologist, though in the strict academic sense, he has no such accreditation.

Before appearing on TV, he worked as a bodybuilding promoter while publishing ''Legendary Times,'' a newsletter about extraterrestrials. He is one of the show's so-called Ancient Astronaut Theorists....