Theory 018/Earth & Space /Geomagnetism
Reversal Rate Tracks the Inner Core
Reversals are attributed to mantle control. The inner core may be the metronome.
The frequency of geomagnetic reversals is set by the growth of the inner core rather than by mantle convection, so the reversal rate should change at the same times as inner-core growth milestones.
01The evidence
The reversal rate has varied over the Phanerozoic, and inner-core growth is thought to have begun and accelerated at particular times.
02The tension
Reversal models invoke mantle heterogeneity or core-mantle heat flux, and the predicted variations do not match the record closely. Inner-core growth changes the dynamo geometry but is rarely the primary variable.
03The mechanism
The inner core provides a boundary that organises the dynamo and stabilises the field. As it grows, the geometry changes and the field becomes more stable, lowering the reversal rate.
That predicts a step in reversal frequency at the onset of inner-core growth, and a further decline as growth accelerates.
04What this is not
Mantle models make reversal a function of boundary heat flux. This makes it a function of inner-core geometry, which predicts steps rather than smooth variation.
05Predictions
- P1Reversal frequency should step at inner-core growth milestones.
- P2The field should be more stable after growth accelerates.
- P3Palaeomagnetic intensity should change with the steps.
06Refutation
Reversal rate varying smoothly with mantle indicators would leave the mantle in control.
07What it changes
It would tie geomagnetic history to core evolution.