The first humans to settle in the Americas crossed the Bering land bridge from Asia, most archaeologists agree, and Norse sailors and Christopher Columbus were among the first Europeans to set foot in the New World. Or so goes conventional wisdom.

But amateur historian and author Gavin Menzies has made a lucrative career upending conventional wisdom, starting with his controversial book "1421: The Year China Discovered the World" (William Morrow, 2002), in which he claims that a Chinese fleet helmed by Admiral Zheng He sailed to the Americas in 1421 and left behind ample archaeological and genetic evidence of their journey.

Menzies' claims were roundly criticized by respected researchers and historians: "The historical equivalent of stories about … close encounters with alien hamsters" is how Felipe Fernandez-Armesto, professor of history at the University of London, described the book, according to the Telegraph. [9 Craziest Ocean Voyages]

Undeterred by relentless, scalding criticism, Menzies — a former sailor with Britain's Royal Navy — went on to write an equally scoffed-at sequel, "1434: The Year a Magnificent Chinese Fleet Sailed to Italy and Ignited the Renaissance" (William Morrow, 2008), and the widely mocked "The Lost Empire of Atlantis: History's Greatest Mystery Revealed" (Harper Collins, 2011).

Now, Menzies is back with a new book, "Who Discovered America: The Untold History of the Peopling of the Americas" (William Morrow, 2013), in which Menzies claims a Chinese map dated 1418 supports his contention that the Chinese were exploring the Americas in 1421, a full 71 years before Columbus' ships set sail.

"The traditional story of Columbus discovering the New World is absolute fantasy, it's fairy tales," Menzies told the Daily Mail, claiming instead that Chinese explorers reached the Americas about 40,000 years ago. "If you just go out in a plastic bathtub, the currents will just carry you there. They just came with the current, it's as simple as that."

The map on which Menzies stakes his claims, however, has been dismissed as a forgery. "Scholars who know this field have refuted this claim under no uncertain terms," Sally K. Church of the University of Cambridge told LiveScience in an earlier interview.

"The map is an 18th-century copy of a European map, as evidenced by the two hemispheres depicted, the continents shown and the nonmaritime [details] depicted," said Geoff Wade, a researcher at the University of Singapore's Asia Research Institute.

Despite his dismissal as a charlatan or, at best, a pseudo-historian, Menzies' books have made him very well-off, prompting historical author Louise Levathes to confess to an abiding respect for Menzies: "His promotional machine is nothing less than extraordinary," she told Salon.

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This story was originally written for Livescience.com and is republished with permission here. Copyright 2012 Livescience.com, a TechMediaNetwork company.