Wow. A really good video.

NOVA says, from the geological record, that when Earth undergoes a polar flip, it looses it's magnetic field for about 3000 years, at least that has been the history.

There's another video I just watched says it takes about 3000 yrs for the Earth and the entire solar system to cross the galactic plane.

So, here's my theory. I think the Earth does a pole shift every time it crosses the galactic plane, and because one has happened about 100,000 years, I think the Earth crosses the galactic plane about that time. In fact scientists really don't know how long is it between crossings (the period of a wave) whenever the Earth crosses the galactic plane, so it could very well be the earth crosses the galactic plane once every 100,000 years and during the 3000 years as it crosses it there is no Earth's magnetic field.