Geophysicists have simulated how Earth's magnetic field could emerge from a fully liquid core, challenging previous assumptions. By minimizing viscosity effects, the model shows a self-sustaining dynamo similar to today's. The findings, published in Nature, shed light on planetary history and future magnetic changes.
Earth's magnetic field protects the planet from cosmic radiation, enabling life as we know it. Scientists have long relied on dynamo theory to explain its generation: swirling convection currents in the liquid outer core, twisted by Earth's rotation, create electric currents that produce magnetism.
A key puzzle was whether this field existed before the solid inner core formed about 1 billion years ago, when the entire core was liquid. Researchers from ETH Zurich and SUSTech in China addressed this in a study published in Nature on October 11, 2025. Using detailed computer simulations, including computations on the Piz Daint supercomputer at CSCS in Lugano, they tested a fully liquid core model.
By reducing viscosity—the internal friction of liquid metal—to negligible levels, the team demonstrated that a stable magnetic field could still arise. This mirrors the dynamo mechanism operating today. "Until now, no one has ever managed to perform such calculations under these correct physical conditions," said lead author Yufeng Lin.
The results suggest Earth's magnetic field formed early in its history through similar processes. Co-author Andy Jackson, Professor of Geophysics at ETH Zurich, noted: "This finding helps us to better understand the history of the Earth's magnetic field and is useful in interpreting data from the geological past."
This early shield likely aided life's emergence by blocking harmful radiation billions of years ago. The model also applies to other bodies like Jupiter, Saturn, and the Sun. For modern implications, the field supports satellite communications and civilization. It has reversed polarity thousands of times, and recent decades show the magnetic north pole shifting rapidly toward the geographic north. Understanding its generation could help predict future changes.
The study, titled "Invariance of dynamo action in an early-Earth model," appears in Nature (2025; 644 (8075): 109, DOI: 10.1038/s41586-025-09334-y).