Geomagnetism
Earth’s magnetic field is dominated by axially symmetric dipolar component
- Other components exist, but are less important
Dipolar axis is not exactly parallel to rotation axis
Curie temperatures and geothermal gradient indicate that there is no bar magnet inside Earth
TRM & DRM provide data on Earth’s magnetic field at different times in the past
- 1500 years ago, field strength = 1.5 x present magnitude
- 5500 years ago, field strength = 0.5 x present magnitude
- Field has always been dominated by dipolar component, with dipole axis parallel to rotation axis on average
- The field has had reversed polarity at different times in the past