A new model uncovers how Earth’s liquid core has sustained its magnetic field since the planet’s beginnings, offering new insights into its future.
Earth benefits from the presence of a magnetic field, which acts as a shield against harmful cosmic radiation and makes life possible. In contrast, planets like Mars are exposed to a constant barrage of charged particles that create a far more hostile environment.
Scientists attribute Earth’s magnetic field to what is known as the dynamo theory. According to this explanation, the slow cooling of the planet’s liquid iron and nickel core drives powerful convection currents in the outer core. As Earth rotates, these flows are deflected, spiraling in screw-like patterns. The motion of the liquid metal generates electric currents, which in turn create magnetic fields, giving rise to most of Earth’s protective magnetic shield.
Yet this theory has a limitation. Before the inner core began to crystallize—an event that occurred about 1 billion years ago—the Earth’s core was entirely liquid. This raises a critical question: could a magnetic field have existed during that earlier period?
A recent study published in Nature offers an answer. In it, three geophysicists from ETH Zurich and SUSTech in China present new insights that shed light on this longstanding mystery.
New model provides the answer
As the Earth’s interior and the processes taking place within it cannot be observed directly, geoscientists study this with the aid of computer models.
The researchers developed a computer model of the Earth with which to simulate whether a completely liquid core could also generate a stable magnetic field. Their simulations were partially calculated on the Piz Daint high-performance computer at the CSCS in Lugano.
In the simulations, the researchers demonstrate the correct physical regime in which the Earth’s core viscosity has no influence on the dynamo effect. This means that the Earth’s magnetic field was generated in the early history of the Earth in a similar way to today.
The research team is the first to successfully minimize the influence of the Earth’s core viscosity to a negligible value in a model. “Until now, no one has ever managed to perform such calculations under these correct physical conditions,” says the study’s lead author, Yufeng Lin.
Understanding the history of the Earth’s magnetic field
“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,” says co-author Andy Jackson, Professor of Geophysics at ETH Zurich.
This also places the emergence of life in a different light. Billions of years ago, life apparently benefited from the magnetic shield, which blocked harmful radiation from space, making its development possible in the first place.
The researchers can also use the new findings to study the magnetic fields of other celestial bodies, such as the Sun or the planets Jupiter and Saturn.
Indispensable for modern civilizations
The Earth’s magnetic field not only protects life, however; it plays a crucial role in making satellite communications and many other aspects of modern civilization possible. “It is therefore important to understand how the magnetic field is generated, how it changes over time, and what mechanisms maintain it,” says Jackson. “If we understand how the magnetic field is generated, we can predict its future development.”
The magnetic field has changed its polarity thousands of times throughout the history of the Earth. In recent decades, researchers have also observed a rapid shift of the magnetic north pole toward the geographic north pole. It is essential for our civilization to understand how magnetism is changing on Earth.
Reference: “Invariance of dynamo action in an early-Earth model” by Yufeng Lin, Philippe Marti and Andrew Jackson, 30 July 2025, Nature.
DOI: 10.1038/s41586-025-09334-y
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