Yes, technically I don’t know that the Earth isn’t a hollow cylinder or something like that. But it’s obvious that the Earth curves, because distant objects fall away over the horizon. Also, if you go to the top of the mountain, you can actually see the Earth’s curvature.
In 240 BC, Eratosthenes not only knew the Earth was round* but calculated its radius to within a few percentage points of truth. In 2017… Teach The Controversy! ™
*technicaly, it’s an oblate spheroid.
