Did lunar tides sustain the early Earth's dynamo?

Abstract

Geological data show that, early in its history, the Earth had a large-scale magnetic field with an amplitude comparable to the one of the present geomagnetic field. However, its origin remains enigmatic and various mechanisms have been proposed to explain the Earth's field over geological time scales. Here, we critically evaluate whether tidal forcing could explain the ancient geodynamo, by combining constraints from geophysical models of the Earth-Moon system and predictions from turbulence studies. Our analysis shows that lunar tidal forcing could have been sufficiently strong before $-3.25$ Gy to trigger turbulence within the Earth's core, and potentially to sustain dynamo action during that interval. Then, we propose new scaling laws for the magnetic field amplitude $B$. We expect the latter to scale as $B\propto {\beta }^{4/3}$, where $\beta$ is the equatorial ellipticity of the liquid core, if the turbulence involves weak interactions of three-dimensional inertial waves. Alternatively, in the regime of strong tidal forcing, the expected scaling becomes $B\propto \beta$. When extrapolated to the Earth's core, it suggests that tidal forcing alone was too weak to possibly explain the ancient geomagnetic field. Therefore, our study indirectly favours another origin for the early Earth's dynamo on long time scales (e.g. exsolution of light elements atop the core, or thermal convection due to secular cooling).

arXiv comment28 pages, 14 figures. Published on 28 January 2026 in C. R. Geosci

References in corpus (37)

• Turbulent geodynamo simulations: a leap towards Earth's core
• Efficient Spherical Harmonic Transforms aimed at pseudo-spectral numerical simulations
• Nitrogen Isotopic Composition and Density of the Archean Atmosphere
• Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
• Spherical convective dynamos in the rapidly rotating asymptotic regime
• Scaling Laws for Planetary Dynamos
• Critical balance in magnetohydrodynamic, rotating and stratified turbulence: towards a universal scaling conjecture
• Force balance in numerical geodynamo simulations: a systematic study
• Elliptical instability in terrestrial planets and moons
• Intertial wave turbulence driven by elliptical instability
• Convective turbulent viscosity acting on equilibrium tidal flows: new frequency scaling of the effective viscosity
• Precessing spherical shells: flows, dissipation, dynamo and the lunar core
• Predictive Scaling Laws for Spherical Rotating Dynamos
• Quantitative experimental observation of weak inertial-wave turbulence
• Structure and decay of rotating homogeneous turbulence
• Tidal dissipation in rotating fluid bodies: the presence of a magnetic field
• Nonlinear tides in a homogeneous rotating planet or star: global simulations of the elliptical instability
• Nonlinear evolution of the elliptical instability in the presence of weak magnetic fields
• A systematic numerical study of the tidal instability in a rotating triaxial ellipsoid
• Precession-driven flows in non-axisymmetric ellipsoids
• Experimental study of the non-linear saturation of the elliptical instability: inertial wave turbulence versus geostrophic turbulence
• Rotating double-diffusive convection in stably stratified planetary cores
• Magnetic fields driven by tidal mixing in radiative stars
• Efficiency of tidal dissipation in slowly rotating fully convective stars or planets
• Fossil field decay due to nonlinear tides in massive binaries
• On turbulence driven by axial precession and tidal evolution of the spin-orbit angle of close-in giant planets
• Inviscid instabilities in rotating ellipsoids on eccentric Kepler orbits
• Turbulent kinematic dynamos in ellipsoids driven by mechanical forcing
• Near-resonant instability of geostrophic modes: beyond Greenspan's theorem
• Scaling laws of turbulent dynamos
• Mean zonal flows induced by weak mechanical forcings in rotating spheroids
• Pressure torque of torsional Alfvén modes acting on an ellipsoidal mantle
• Geomagnetic dipole stability and zonal flows controlled by mantle heat flux heterogeneities
• Tidal dissipation due to the elliptical instability and turbulent viscosity in convection zones in rotating giant planets and stars
• The interactions of the elliptical instability and convection
• Electrical and Thermal Conductivity of Earth's Iron-enriched Basal Magma Ocean
• Dynamic regimes in planetary cores: τ-{\ell} diagrams