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Ancient geodynamo: the problem and the new solution
The Earth’s magnetic field is a vital shield that protects the atmosphere and surface life from high-energy charged particles and cosmic radiation. Modern understanding attributes this protective field to a geodynamo operating in the planet’s liquid outer core: convective flows of electrically conductive iron–nickel generate electric currents that sustain the magnetic field as the planet rotates. However, a long-standing paradox has persisted. The geodynamo model that explains today’s field relies in part on the energetics associated with the crystallization of a solid inner core—an event thought to have begun roughly one billion years ago. Prior to that time the core was fully liquid, raising the question: could a purely liquid core sustain a long-lived, stable magnetic field?
A recent peer-reviewed study by researchers at ETH Zurich and Southern University of Science and Technology (SUSTech) provides a compelling answer. Using large-scale numerical simulations, the team demonstrates that the early Earth could indeed have maintained a strong geodynamo without a solid inner core. Their results reconcile paleomagnetic evidence of an ancient magnetic field with dynamo theory and offer new constraints on the thermal and compositional evolution of Earth’s interior.
Modeling the liquid core: methodology and technical advances
Geophysical processes in Earth’s deep interior cannot be observed directly, so high-fidelity computer models are essential. The ETH–SUSTech team developed a numerical model that explores the physical regime where the effective viscosity of the core is negligible for dynamo action. Prior models often retained artificially high viscosities for numerical stability, which can alter the convective patterns and magnetic behavior. By pushing simulations closer to Earth-like parameters and minimizing the impact of viscosity, the researchers reproduced the dynamo mechanism in a fully liquid core.
These simulations were partially executed on Piz Daint, the Swiss National Supercomputing Centre’s (CSCS) flagship high-performance computer located in Lugano. The computational work required resolving turbulent, three-dimensional flows and magnetic induction across a wide range of length and time scales. "Until now, no one has ever managed to perform such calculations under these correct physical conditions," said lead author Yufeng Lin, describing the significance of reaching the low-viscosity regime in the model. Co-author Andy Jackson from ETH Zurich adds that the results enable more reliable interpretations of geological magnetic records.
Key findings and scientific implications
The simulations show that, under appropriate thermal and compositional buoyancy conditions, convective motions in a fully liquid core can self-organize into the screw-like, columnar flows associated with an efficient dynamo. In other words, the geodynamo does not require solid inner-core growth to operate; instead, magnetic field generation in early Earth could have been driven by thermal convection and compositional heterogeneity alone. This resolves a major discord between dynamo theory and paleomagnetic evidence indicating an ancient, sustained field.
Implications are broad: the presence of a magnetic shield early in Earth’s history would have reduced atmospheric erosion and radiation exposure on the surface, improving conditions for the emergence and persistence of early life. The findings also refine models of core cooling rates and composition, which feed into broader models of planetary evolution.
Expert Insight
Dr. Maya Rinaldi, a planetary physicist not involved in the study, commented: "This work is a major step toward bridging numerical geodynamics and the geological record. Demonstrating a viable dynamo in a fully liquid core reshapes our timelines for thermal evolution and helps explain how early habitability conditions may have been maintained on Earth." Her remarks underscore how advances in supercomputing and model realism are changing our view of planetary magnetic histories.
Relevance for other planets and modern technology
The study’s approach and conclusions extend beyond Earth. The same modeling framework can be adapted to explore magnetic fields of other planetary bodies—gas giants with deep conducting layers or rocky planets with differing thermal histories. Understanding the mechanisms that sustain planetary magnetic fields is also practically important: Earth’s magnetosphere supports satellite communications, navigation systems, and electrical infrastructure by shielding the near-Earth environment from charged-particle hazards. Improved predictions of field evolution and polarity reversals depend on accurate geodynamo models.
Conclusion
By demonstrating that a fully liquid core can generate a stable geodynamo when modeled under near–Earth physical conditions, researchers from ETH Zurich and SUSTech have closed a key gap in our understanding of Earth’s deep past. Their simulations reinforce the idea that a protective magnetic field existed long before the inner core began to crystallize, with important consequences for early habitability, planetary evolution, and our ability to interpret magnetic signals preserved in rocks. Future work will refine these models further and apply the same methods to other planets and stars to map how magnetic dynamos operate across the Solar System.
Source: scitechdaily
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