Figure 14.13Earth’s magnetic field changes over time. Blue colors show the strength of the inward-pointing field, and orange colors show the strength of the outward-pointing field. The magnetic field mapped at the surface (b) is more complex than a simple dipole (a), and it shows more complications when extrapolated to the core-mantle boundary (c). The features on the nondipole field change over time, as seen in (c) through (e), owing to convection in Earth’s fluid outer core.