Map Proof Chinese Discovered America?

Its owner says this map changes history. But skeptics say he's way off course.
Antiquities collector Liu Gang unveiled the map in Beijing on Monday, saying it proves that Chinese seafarer Zheng He discovered America more than 70 years before Christopher Columbus set foot in the New World.
The map depicts all of the continents, including a small Australia, a roughed-out North America, and Antarctica.
An inscription identifies the map as a copy made in 1763 of an original drawn in 1418.

If verified, that date would coincide with the voyages of Zheng He, an admiral in the Ming dynasty's imperial navy. Zheng is known to have sailed as far as Africa between 1405 and 1433.
(See National Geographic magazine feature: "China's Great Armada.")
A lab in New Zealand is radiocarbon-dating a scrap of the map's bamboo paper to determine its age.
Liu says he purchased the map from a dealer in Shanghai in 2001 but didn't suspect its importance until he read 1421, a book that claims Zheng discovered America.

The book, written by retired British Navy officer Gavin Menzies, also asserts that Zheng was the first to circumnavigate the globe and that Chinese settlers established now-vanished colonies throughout the Americas.
Many scholars, including Chinese historians, have dismissed these claims.

"I sincerely believe that other maps exist and books exist [that support the claims], but no one has been paying attention to them," Liu told the AFP news agency. "It is my purpose to try to wake these [scholars] up."
—Blake de Pastino