This has now been proven without a doubt.
ArchaeologyAshNews writes at Set Sail for Singapore! about the recent discovery of an ancient sailing vessel, the cargo of which convincingly proves ancient world seafaring long before the modern era.
That posting is about:
"[T]he 1998 discovery of a ninth-century shipwreck and its astonishing cargo of about 60,000 objects from Tang dynasty China, ranging from mass-produced ceramics to rare and extraordinary items of finely worked gold. The cargo had laid undisturbed on the ocean floor for more than 1,100 years until sea-cucumber divers discovered it off the coast of Indonesia's Belitung Island. The ship, an Arab dhow, and its contents confirm the existence of a direct maritime trade route (alluded to in ancient Chinese and Arabic texts) from China to the Persian Gulf and beyond-well before the Portuguese set sail in the 15th century."For the original story, see ArtKnowledgeNews.com at
Smithsonian and Singapore Organize World Tour of Shipwreck Treasure