today it is already proven that the earth is a sphere shaped. it is given that the shape is proven because of science, and astronauts outside the earth could tell you the proof. but even along time ago, around 1500's, Ferdinand Magellan had an expedition, a circumnavigation the first voyage, he only headed to one direction. He was fascinated that he came back to the same place he started and concluded that the earth is round. this is a proof that the Flat earth theory is not a theory anymore for it is proven wrong.