The peoples of Micronesia, Melanesia, and Polynesia explored the Pacific long before the Europeans sailed upon it, but the Pacific was the last major portion of the earth's surface to become known to other than local inhabitants. Greek geographers, without actually knowing of such an ocean, reasoned that it must exist and named it the Eastern Ocean to balance the Western Ocean or the Atlantic. Arabian geographers learned much more about this ocean and renamed it the Green Sea. Marco Polo and his contemporary travelers brought back to Europe evidence that this ocean existed and descriptions of some of the islands close to Asia such as Japan and the East Indies. The Arabian and medieval travelers found that the ocean was traveled by Chinese vessels. How far back this Chinese navigation extends cannot be determined from present information, but it is evident from archeological evidence that the Chinese had contact at least with Java, the Philippines, and Japan as early as the Han Dynasty ( 200 B.C. to A.D. 221).
Before the Age of Discoveries, European geographic speculation placed a great ocean extending unbroken from Europe to the shores of Asia. This is shown on the Martin Behaim globe of 1492, which represents the concepts of the world developed by speculation on the part of Greek, European, and Moslem geographers up to the time of Columbus's voyage. As a result of Marco Polo's voyages Sumatra appears as Java Minor and Java as Java Major on the globe.
With the Age of Discoveries, the Americas were soon found to impose a barrier between the Eastern and Western oceans. On September 25, 1513, Vasco Núñez de Balboa crossed the isthmus of Panama and was the first European to see the Eastern Ocean from the New World. Since Balboa sighted the ocean to the south of a point where the isthmus of Panama runs east and west, the ocean was named the South Sea, and this name has continued to be applied to part or all of the ocean from the Arctic to the Antarctic. At about the same time, the ocean was entered from the other side. The Portuguese who had reached Malacca in 1509 pushed on from there, and in 1512 two of their captains, Abreu and Serrano, sighted New Guinea, although it was not until 1526that Meneses actually visited its shores. The Portuguese pushed up the coast of Asia, reaching Canton in 1514 and Japan in 1542.