Early traders navigated the seas with the of the big dipper north star orion milky way

North Star. Orion and the Big Dipper are constellations (well, the big dipper is an asterism, but that's irrelevant), and the Milky Way is our galaxy. The only one that assists with navigation is the North Star, because it always, you guessed it, points North. Once North is located, the assistance of the passage of time combined with cartography and a bunch of other stuff can allow a navigator get his/her bearings.

The exchange of foods between the new and old worlds