"We spend a great deal of time studying history," Stephen Hawking said in a 2016 lecture, "which, let's face it, is mostly the history of stupidity." Smart man, that Hawking. It may seem cynical to take this approach, but you'll find after scanning the beliefs of the past that it's a pretty spot-on assessment.
Let us now take a moment to mourn nine debunked and disproved theories of the past. Hope you're ready for a spook, because nothing is scarier than scientific inaccuracies! Rest in peace, dumb beliefs about the world; no longer shall you live in the collective consciousness of society.