A fully liquid Earth’s core also generates a magnetic field
For more than 100 years, scientists have puzzled over whether the Earth’s magnetic field had already been generated stably back in its early days when its inner core was fully liquid – unlike it is today. A team of geophysicists has used a simulation to show that this was highly likely.
In brief
- Geophysicists from ETH Zurich and SUSTech, China, have demonstrated the dynamo effect of the Earth’s core in a model in which viscosity has no influence, as is the correct physical regime for the Earth.
- The magnetic field was created in the Earth’s early history when its core was completely liquid in a similar way to today.
- This finding helps us to better understand the history of the Earth’s magnetic field and make more precise predictions of its future development.
The Earth is fortunate in having a magnetic field: it protects the planet and its life from harmful cosmic radiation. Other planets in our solar system – such as Mars – are constantly bombarded by charged particles that make life difficult.
Scientists explain the generation of the magnetic field by the mechanism known as the dynamo theory. This states that the ongoing slow cooling of the liquid iron and nickel core drives circular currents of liquid material in the outer core known as convection currents. At the same time, the Earth’s rotation deflects these currents, causing them to flow in a screw-like pattern. These convection currents generate electric currents, which in turn produce magnetic fields and thus most of the Earth’s magnetic field.
However, the theory has a flaw: the Earth’s core was completely liquid before the Earth’s inner core crystallised – around 1 billion years ago. The question is whether the magnetic field could have been generated prior to this time.
A team of three geophysicists from ETH Zurich and SUSTech, China, have come up with an answer to this question in a new study published in the journal Nature.
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 minimise 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 civilisations
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 civilisation 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 civilisation to understand how magnetism is changing on Earth.
This study was funded in part by an ERC Advanced Grant awarded to Andy Jackson in 2019.
Reference
Lin Y, Marti P, Jackson A, Invariance of dynamo action in an early-Earth model, Nature (2025), doi: external page 10.1038/s41586-025-09334-y