Also known as planet X, Nibiru is the 12th planet in our solar system. Every 3000 years or so, it comes between Earth and the sun and has an effect on Earth. Please read more below, to understand.
"What Will Be the Effects on Earth?
As stated before, the gravitational pull of a planet entering the inner solar system would have profound effects on the other orbiting bodies, including Earth. In fact, the Anunnaki story says that a previous appearance of Nibiru was responsible for the "Great Flood" recorded in Genesis, in which nearly all life on our planet was extinguished (but saved, thanks to Noah). Going even further back, some researchers into this topic suspect that Nibiru once even collided with Earth millions of years ago, creating the asteroid belt and resulting in the enormous gouges in our planet that the oceans now fill.
Mark Hazelwood and others say that Earth is in for some massive and catastrophic changes as Nibiru approaches. Floods, earthquakes, volcanic eruptions, a pole shift and other natural disasters will be so severe, Hazelwood says, that "only a few hundred million people will survive." Another site says the gravitational pull of Nibiru might even stop the Earth's rotation for three days, citing the "three days of darkness" predicted in the Bible.
Some of the Nibiru researchers also cite the prophecies of Edgar Cayce who predicted that we would soon suffer monumental Earth changes and a pole shift, even though he did not attribute them to anything as specific as a visiting planet. And, of course, the much-analyzed Mayan calendar is said to set the "end of world" in December, 2012.
Astronomers and other scientists who would seem to be in a position to know such things have made no announcements about the approach of any planet-sized body. Apparently, they have not detected anything of the kind. Those who believe Nibiru is approaching, however, say that scientists do know all about it and are just covering it up.
As with any such predictions, time will tell."
(cited; http://paranormal.about.com/library/weekly/aa021102b.htm)
