# Geomagnetic reversal?

I have always been told that the geomagnetic field acts "as if" there were a bar magnet inside the Earth. I now this is not true, but I feel that knowing what is actually going on would help me understand the answer to the question that I'm about to ask:

Why does geomagnetic reversal happen? Is it something gradual or relatively fast?

(What is the origin of the geomagnetic field? Can we answer my questions starting from this mechanism?

• Most estimates for the duration of a polarity transition are between 1,000 and 10,000 years. Source: a not very reliable site (but do check its sources in turn). – Renan Jul 25 '14 at 18:41