The fact that it's existed for billions of years means something must be regenerating it all the time. To the consternation of our desire to understand what's happening inside the planet we live on, Jules Verne's Journey to the Center of the Earth is still fiction. There's no way to penetrate 4,000 miles to Earth's center, nor to monitor fluid motions or magnetism in the outer core. The Glatzmaier-Roberts computational model may be the next best thing to a guided tour of inner Earth. While other models have given good clues that theory is on track, they have been limited by a two-dimensional approach that required simplifying assumptions.
Field lines extend two Earth radii from the core.
The location of the core-mantle boundary is evident where the structure becomes complex. Their objectives, in retrospect, were modest. No one's ever done that in a self-consistent manner. After nearly a year running almost daily, as allocated computing time was about to expire, the model produced its Eureka moment. The simulation also offers precious insight into the dynamics that sustain the magnetic field and generate reversals.