Energetically expensive dynamo action in Earth's basal magma ocean.

Area of Science:

• Geophysics
• Planetary Science
• Dynamo Theory

Background:

• Previous research suggested basal magma ocean (BMO) convection could generate Earth's ancient geomagnetic field.
• The electrical conductivity and thermal evolution of the early BMO are key factors in dynamo generation.

Purpose of the Study:

• To investigate the potential of BMO convection to generate an Earth-like magnetic field using advanced dynamo modeling.
• To assess the influence of planetary rotation and thermal evolution on BMO dynamo processes.

Main Methods:

• High-resolution dynamo modeling of convection in a thin, BMO-like spherical shell.
• Integration of dynamo results with thermal evolution models.
• Application of rotating convective turbulence models to account for Earth's rapid rotation.

Main Results:

• Convection in a thin BMO-like shell can sustain strong magnetic fields, including axial dipolar fields.
• However, incorporating realistic thermal evolution and rapid rotation suggests an Earth-like magnetic field was unlikely generated in the BMO.
• BMO-type dynamos require a larger product of electrical conductivity and velocity than core-type dynamos and are rotationally constrained, reducing velocities.

Conclusions:

• The generation of an Earth-like magnetic field in the basal magma ocean is unlikely.
• Findings impact the interpretation of ancient paleomagnetic signatures and understanding of early Earth dynamics.
• Further research requires refined deep Earth models, accurate convective scaling laws, and coupled core-BMO dynamo simulations.