There's a whole subjection on the FAQ that I believe is in the same camp as your question http://www.reddit.com/r/AskHistorians/wiki/dailylife#wiki_early_ideas_about_aliens_and_ufos

Sorry, we don't allow throughout history questions. These tend to produce threads which are collections of trivia, not the in-depth discussions about a particular topic we're looking for. If you have a specific question about a historical event or period or person, please feel free to re-compose your question and submit it again. Alternatively, questions of this type can be directed to more appropriate subreddits, such as /r/history or /r/askhistory.

This is a question about possible events that long predate human history. It would be better to ask in /r/Askanthropology, or maybe /r/paleontology?