10. Round earth
This is an idea that is fully accepted by most people, but it was not always held with such certainty. While it is a misconception to think that most people believed in a flat earth well into the early modern period, it was certainly a commonly held belief in early Chinese
thought, and it was not until the great Greek mathematicians that Europeans started to accept the spherical earth theory. Pythagoras is the man most commonly associated with the idea, but it was really only in the Renaissance, and the beginning of voyages that circumnavigated the earth, that his ideas became proved beyond all doubt.