In the Biblical account of creation, G-d divided the waters. The rabbi and Biblical commentator Nachmanides wrote about this that he believes the Greek demonstration that the earth is mostly covered with water.
I've been thinking about this statement. At first blush, the portion of the earth covered with water obviously seems to be an empirical question which could not be resolved by any logical argument. But I wonder whether Nachmanides was thinking of an ancient computation about the size of the earth (based on sun angles establishing the degrees of arc between two places at a known distance), coupled with the assumption that someone sailing west from Europe would encounter no land for most of the way to Japan, as apparently anyone would have thought who was unaware of the Americas.
(He would also need some opinion about the size of the known world, but apparently this is the easy part.)
Is there any way of identifying this argument with any greater specificity? What works of Greek geography (or what would the word be?) were available to Nachmanides, and which of these dealt with the question of the amount of the earth's surface covered by water? How widely shared was this opinion?