ALL the predictions for the end-of-the-world of 2012 were invented during the summer of 2003 and after.
The Big 2012 Hoax itself was created by the same people who had made money from the Planet-X hoax, up to June 2003.
According to the original hoax (based on the dreams of Nancy L.), Planet X was to pass too close to Earth in May-June 2003 and cause all kinds of problems (global tsunami, crust shift, pole shift, hide the sun for months...), most of which were used in Roland's movie "2012".
The charlatans who made money with this hoax were selling books on how to survive, and selling seats on alien spacecrafts sent to save some of us (Roland changed them into the "Arks", the barges that would ride out the tsunami).
After June 2003, the money stopped coming in. So the charlatans needed a new hoax.
They picked the date from another lie (the Mayan calendar does not really end) and then modified a bunch of existing hoaxes, lies and stories, to make them fit their new hoax. Once the Big 2012 Hoax became popular, other charlatans invented new hoaxes (or modified their earlier ones) so that they would fit with the new date.
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In the late 1980s, a dude wanted to sell books on his 'esoteric' new-age-type predictions. This guy claimed to be a reincarnated Mayan priest (he is not -- he was born in Minnesota) and wrote a book about his "interpretations" of ancient Central-American calendars. Among other lies, he invented the idea that a Mayan calendar, called Long Count, ends. He picked a date on which the calendar passes a round figure (there is a round figure every 394 years and a quarter).
Our Calendar = Mayan Long Count
2012.12.20 = 12.19.19.17.19
2012.12.21 = 13.00.00.00.00
2012.12.22 = 13.00.00.00.01
and it continues...
with the next round figure to be in early 2407.
When the Planet-X charlatans picked this date for the Big 2012 Hoax, they were the ones who added the idea that end-of-calendar = end-of world.
José, the fake Mayan priest, had simply said that the end of the calendar promised a new chance for a humanity liberated from the old calendar.
The real Mayans (knowing that their calendar really continued) made no such predictions -- no end-of-the-world, no new-age-humanity-will-be-saved predictions.
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Back to the Big 2012 Hoax and the Planet-X charlatans:
They then proceeded to take existing hoaxes, lies and stories, and change them to fit their new hoax.
Here are a few examples:
Nibiru: from a story written in the 1960s. In that story, Nibiru is a planet that comes near Earth every 3700 years; the next passage cannot be before the year 2085. When it does pass close to us, it cannot harm us: the people on Nibiru need our help in order to survive their very long winter (3698 years).
The charlatans needed some ideas and data from the Nibiru story, so they stole it (without the original author's permission -- that is why Roland did not use it in his movie); they even stole the name Nibiru and used it for their hoax.
Photon belt: originally invented in Germany in 1949. The more 'modern' version (invented in the mid 1980s) claims that when we cross this photon belt, the force will modify us and make all humans much better (war and poverty would disappear, and so on).
According to the couple who made up the original version, Earth was to enter the Photon Belt in May 1997. I'm still waiting for the improvements...
The Bible Code was an exercise in statistics, published in a journal in 1994. The idea was to show that you can create order from a random set of elements, as long as the source of random elements is large enough. A very basic example of the exercise is: take the Bible as a source of letters (it certainly contains a lot of letters). Then take a regularly-spaced sampling (for example, every tenth letter). If you do this often enough, and with different methods, you will eventually form sentences that were not contained in the text.
The idea was to show the dangers of using that type of sampling method.
Sure enough, some charlatan actually believed the statements they found using this method, and published them as secret prophesies hidden in the Bible. World War 3 was to being in the year 2000 and end in a Global Nuclear Holocaust in... 2006.
The charlatans who made up the Big 2012 Hoax simply say that the Bible Code predicts the end-of-the-world of 2012. They don't even bother to say how they applied the code to get the prediction. They just made it up.
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BTW, when Planet X failed to show up in 2003, Nancy said that the aliens told her (in a dream, again) that they had made a small mistake and that the planet was coming in 2011. But by the time she had made that announcement, her "friends" has already created the Big 2012 Hoax.