• Persistence of a magnetic field
throughout geological history
– Age of the magnetic field is >3.5Ga
– Dominance of the dipolar part of the field
– Relaxation time of the dipolar field in the
core is ~20,000 years
– Averaged over 10,000 yrs, the field is
represented to 95% by an axial dipole
centered at the earth’s center, the GAD
– Dipolar field has not changed with geological
time: dipole moment ~7.8 1022 Am2
Characteristics of the earth’s magnetic field
GAD= Geocentric Axial Dipole
Docsity.com
