New simulation reveals how Earth’s magnetic field first sparked to life

Scientists have long explained the source of this protective force through the dynamo theory, which describes how motion within Earth's liquid metal core creates magnetism. As the molten iron and nickel slowly cool, they form swirling convection currents in the outer core. The planet's rotation then twists these flows into a spiraling, screw-like pattern. These moving, electrically conductive materials generate electric currents that produce magnetic fields -- together forming most of Earth's overall magnetic field.

Yet the theory raises a problem. Before Earth's solid inner core began to crystallize (about 1 billion years ago), the entire core was liquid. Could the planet's magnetic field have existed even then?

A group of three geophysicists from ETH Zurich and SUSTech, China, set out to answer this question in a study published in Nature.

New model offers fresh insight

Because scientists cannot directly observe the processes deep inside Earth, they rely on computer simulations to model its internal dynamics.

In this new work, the team built a detailed digital model of the planet to test whether a fully liquid core could still maintain a stable magnetic field. The calculations, some performed on the Piz Daint supercomputer at the CSCS in Lugano, revealed that magnetism can indeed arise even when viscosity -- the internal friction of the liquid metal -- has no measurable effect on the process. This finding suggests that Earth's magnetic field likely formed early in its history through mechanisms very similar to those still operating today.

Remarkably, the researchers were the first to show that viscosity could be reduced to an almost negligible level in such models. "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 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 civilization to understand how magnetism is changing on Earth.

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.