The Long-Term Survival of Earth’s Magnetic Field


Earth’s core has generated a magnetic field for billions of years. However, the nature of that field has varied considerably through time for reasons that are still poorly understood. Both the average strength of the field and the average frequency of geomagnetic reversals have changed over timescales of 100s of millions to billions of years. These changes relate to fundamental questions about the evolution of Earth’s deep interior, such as the influence of the mantle on core convection and the age of the inner core.

The timescales over which the paleomagnetic field characteristics change are much longer than any timescales associated with the internal dynamics of the convecting liquid iron outer core and thus are likely related to external factors arising from the thermochemical evolution of the planet.

One possible explanation for these very long timescale changes is the initiation and ongoing crystallisation of the inner core. This changes both the geometry of the system (full sphere vs spherical shell) and the distribution of buoyancy that drives convection (by releasing latent heat and light elements at the inner core boundary).

Another possibility is changes in core-mantle interaction. Just as mantle convection alters the distribution of continents over geologically long timescales, so too does it alter the pattern and amplitude of heat flow extracted across the core-mantle boundary.

Output from a numerical simulation showing the impact of hot mantle on the dynamics in Earth's core. Hot mantle results in weaker flows and magnetic fields in the core.
Output from a Leeds dynamo simulation showing the fluid flow (left) and magnetic field (right) at the top of Earth’s core. The behaviour of the core is different under regions of particularly hot mantle (black contours).

Project Goals

In this project you will investigate how the long-term evolution of the core. For example, changes in the size and growth rate of the inner core and the heat extracted from the core by the mantle) are expected to influence Earth’s magnetic field. A combination of increased computing power (enabling simulation of more Earth-like conditions) and better theoretical understanding (allowing more robust extrapolations of those simulations) mean that we are now well placed to investigate these questions.

You will run new simulations that describe the detailed process of magnetic field generation on geologically short (decadal to million-year) timescales. Next, you will extrapolate the simulated fields to planetary core conditions and couple these results to models of Earth’s thermal history to predict the long-term evolution of the paleomagnetic field. Finally, you will compare these model predictions to paleomagnetic observations, building on established collaborations between Leeds and colleagues at the University of Liverpool and the Scripps Institute of Oceanography.

Overall, through this project you will shed new light on fundamental questions in deep Earth geophysics. You will improve our understanding of the influence of the mantle on core convection, the age of the inner core, how Earth’s magnetic field has been powered over billions of years, and why its fundamental characteristics change through time.

Related reading:

Biggin, A. J. et al. Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation. Nature 526, 245–248 (2015).

Davies, C. J. et al. Dynamo constraints on the long-term evolution of Earth’s magnetic field strengthGeophys J Int 228, ggab342- (2021).

Greenwood, S., Davies, C. J. & Mound, J. E. On the evolution of thermally stratified layers at the top of Earth’s corePhys Earth Planet In 318, 106763 (2021).

Landeau, M. et al. Sustaining Earth’s magnetic dynamo. Nat Rev Earth Environ 3, 255–269 (2022).

Meduri, D. G. et al. Numerical Dynamo Simulations Reproduce Paleomagnetic Field BehaviorGeophys Res Lett 48, (2021).

Pétrélis, F., Besse, J. & Valet, J. P. Plate tectonics may control geomagnetic reversal frequencyGeophysical Research Letters 38, L19303 (2011).