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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, 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 Earth's magnetic field.

However, the theory has a flaw: Earth's core was completely liquid before Earth's inner core crystallized—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 in the journal Nature.

New model provides the answer

As 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 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 Earth's core viscosity has no influence on the dynamo effect. This means that Earth's magnetic field was generated in the early history of Earth in a similar way to today.

The research team is the first to successfully minimize the influence of 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 Earth's magnetic field

"This finding helps us to better understand the history of 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

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 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.