EARTH In the literature: open

What triggers geomagnetic polarity reversals and sets their rate

In plain words

The magnetic poles have flipped hundreds of times at irregular intervals, sometimes several times per million years and sometimes not at all for tens of millions of years. The flow pattern in the liquid core that starts a flip is unknown.

Precise statement

The axial dipole reverses irregularly, at a mean rate of roughly 4 to 5 per Myr over the last few Myr and essentially zero during superchrons such as the Cretaceous Normal Superchron (about 121 to 83 Ma). Identify the magnetohydrodynamic mechanism in the rotating, convecting outer core (Ekman number $E \sim 1e-15$, magnetic Prandtl number $\mathrm{Pm} \sim 1e-6$) that initiates reversals and controls their rate. An answer is a mechanism demonstrated in dynamo simulations at Earth-like parameter ratios that reproduces the observed reversal statistics (rate, duration of transitions, excursion frequency).

What would settle it

Dynamo simulations in the rapidly rotating asymptotic regime that reproduce paleomagnetic reversal-rate and transition statistics with an identified triggering flow.

Status in the literature

Unverified note

2025 simulation studies (e.g. arXiv:2505.05221) link reversals to core-surface flow kinematics, but no mechanism has been confirmed at Earth-like parameters.