Yesterday, Jason Colavito posted a brilliant article contesting a claim that an Arab navigator made his way to America in 999 CE. The claim had made its way to Wikipedia, and has cropped up elsewhere. Colavito's takedown is excellent, and I recommend reading it.
Check out the rest of Colavito's website, as well. There's really no reason for anyone else to go about debunking Ancient Aliens when Colavito has already done the hard work for us.