OT: Earth's orbit changing?

[Kamog]

I never understood this idea of the earth's magnetic poles moving around. How can the magnetic field, which was stable for a long period of time, suddenly reverse polarity? If the magnetic field is produced by the flow of molten material inside the earth, then it takes a tremendous amount of energy to change the direction of flow for so much mass. Where does this energy come from? Also, I thought that a flow of material will not produce a magnetic field unless there's an electrical current flowing through it. I mean, if you take a piece of iron and move it around where there's no magnetic field, it's not going to produce its own magnetic field, would it?