Zecharia Sitchin was an author of a number of books proposing an explanation for human origins involving ancient astronauts. Sitchin attributed the creation of the ancient Sumerian culture to the Anunnaki, which he claimed was a race of extraterrestrials from a planet beyond Neptune called Nibiru. Wikipedia

Sitchin states that when struck by one of planet Nibiru's moons, Tiamat split in two, and then on a second pass Nibiru itself struck the broken fragments and one half of Tiamat became the asteroid belt. The second half, struck again by one of Nibiru's moons, was pushed into a new orbit and became today's planet Earth.

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