DID THE CHINESE DISCOVER AMERICA?

ALONG of history,we have known about discovery of AMERICA by CHISTOPHER COLUMBUS but according to GAVIN MENZIES chinese explored AMERICA before  CHRISTOPHER COLUMBUS.MENZIES has made some theories about discovery.HE said that when the spanish colonialists come to the region in the sixteenth century,they met descendants of the chinese mariners and diseases were spread by themselves which wiped out 90% of native populatrion besides MENZIES alleged  that NICOLO da CONTI (who was traveling with ZHENG HE,the first chinese explorer)brought the maps to VENICE in1428 for this reason CHRISTOPHER COLUMBUS had the map of AMERICA.