One of my high school classmates majored in geology in college. No one ever convinced him that the earth was not flat.
He took Revelations 7:1 literally:
1And after these things I saw four angels standing on the four corners of the earth, holding the four winds of the earth, that the wind should not blow on the earth, nor on the sea, nor on any tree.
His reasoning was the earth could not have four corners if it was round............