JACKSON: Hey, the world was flat until someone took a boat trip.
Jackson is promoting the modern misconception that people in the Middle Ages commonly believed that the Earth is flat. In fact people have known that the Earth is spherical since the Ancient Greeks – the mathematics to prove it aren’t particularly difficult. The myth seems to date from the 17th century, as a Protestant campaign against Catholic teaching.
The idea that it was the voyage of Christopher Columbus to the New World which changed everyone’s mind about the flat Earth comes from Washington Irving’s 1828 biography, A History of the Life and Voyages of Christopher Columbus.
Highly romanticised, it contained fictional scenes where some of the Spanish disagreed that the Earth was spherical. Even Irving pointed out that a flat Earth theory didn’t affect Columbus’ navigation, but rather the limited understanding of Earth’s size and position of the continents.
The Annotated Gilmore Girls 