Ancient Chinese explorers

I just finished reading an interesting book called "1421 The Year China Discovered America". The author (Gavin Menzies) makes the claim that during the period of about 1400 to 1421 China sent out huge flotillas (hundreds of very large ships) to explore the earth from top-to-bottom (or maybe stem-to-stern). If his thesis is correct, they explored and influenced cultures in all major parts of the world, including the east and west coast of America, South America and others. It is a very interesting book, well worth the time to check it out. I would like to do a little independent research to check some of his references to try to convince myself that it isn't completely made up. It sounds like it is factual, seems to make sense, and "feels right" to me - but there are always hoaxes to deal with.

One of the things that it points out is that there was a whole lot more ocean traveling going on than we know about, or have been told about in school. I have always been convinced that the three major parts of the world have been much more tightly connected than we have been told. For example, it seems very likely that the Egyptians took their very large and seaworthy vessels out into the Atlantic. If they did that, there is nothing stopping them from going to South America and then back home again. In fact, it is almost difficult not to do that considering the ocean currents and winds. Once you get out in the ocean you naturally going around in the big circle. All you have to do is be able to stay alive long enough to make the trip, and it will be made. It looks to me like their 150+ foot ships were perfectly capable of doing that. This kind of trip would help explain the ancient corn that has supposedly been found in the tombs in Egypt. Corn only comes from South America and requires man to plant it (it doesn't propagate on its own). Therefore, if there really was corn (maze) in the Egyptian tombs, it had to have been brought there by someone - and that someone had to have gotten it from South America. This all makes perfectly good sense once you come to the conclusion that the old people traveled across the oceans. The same kind of thing happens in the Pacific Ocean. If you put a boat in the ocean somewhere around Japan you will go north to Alaska, down the west coast of the US, down to about Panama and then back home again.