 The main part of Earth 's magnetic field is generated in the core , the site of a dynamo process that converts kinetic energy of fluid convective motion into electrical and magnetic field energy . The field extends outwards from the core , through the mantle , and up to Earth 's surface , where it is , to rough approximation , a dipole . The poles of the dipole are located close to Earth 's geographic poles . At the equator of the magnetic field , the magnetic @-@ field strength at the surface is 3 @.@ 05 × 10 − 5 T , with global magnetic dipole moment of 7 @.@ 91 × 1015 T m3 . The convection movements in the core are chaotic ; the magnetic poles drift and periodically change alignment . This causes field reversals at irregular intervals averaging a few times every million years . The most recent reversal occurred approximately 700 @,@ 000 years ago . 
