Earth magnetic field is produced by relative movement of crust and liquid molten iron nucleus (dinamo effect) and it is variable in time and space. Its intensity varies from poles to equator between 25.000 si 65.000 nT (1 nT=10-6 gauss). Geomagnetic field intensity and direction periodic change. The pole positions are variable, without a cyclic determination, and they are important elements of paleomagnetism.
