Earth’s Magnetic Field Mystery Finally Solved: New Study Explains How It Worked a Billion Years Ago

The Earth’s magnetic field is one of the most crucial shields protecting our planet from harmful cosmic radiation. Without it, Earth would be bombarded by charged particles from the Sun and beyond, stripping away the atmosphere and making life as we know it almost impossible. This invisible shield has puzzled scientists for decades, especially when it comes to how it functioned in the deep past.

A recent study published in Nature by researchers from ETH Zurich and Southern University of Science and Technology (SUSTech) in China has taken a big step in solving this puzzle. The work focuses on a time before the Earth’s inner core crystallized — around 1 billion years ago — when the core was thought to be entirely liquid. The key question has always been: how could Earth have sustained a magnetic field at that time?

Earth’s Magnetic Field Mystery Finally Solved: New Study Explains How It Worked a Billion Years Ago

The research team, using advanced computer simulations, now provides a convincing answer. Their results show that even with a completely liquid core, Earth could maintain a strong and stable magnetic field. This finding changes how we understand the planet’s history and its ability to support life, while also opening doors to new studies of magnetic fields on other planets.

Why the Magnetic Field Matters

Earth’s magnetic field is generated by a process known as the geodynamo. It works like this: the slow cooling of the liquid iron and nickel core sets up convection currents in the outer core. As the Earth rotates, these currents spiral and twist, generating electric currents, which in turn create magnetic fields. This self-sustaining process has kept our magnetic shield alive for billions of years.

Without this protection, Earth would resemble Mars, which lost its global magnetic field long ago. Mars is constantly exposed to solar wind, and as a result, much of its atmosphere was stripped away. This left it with a harsh, cold environment not suited for life on the surface. The comparison highlights just how critical Earth’s magnetic field is — not just for shielding life but also for making life possible in the first place.

The Problem with the Traditional View

The standard explanation of the geodynamo works well for modern Earth, where a solid inner core exists. The crystallization of the inner core provides additional energy that powers the convection in the outer core. But here’s the problem: geological evidence shows Earth had a magnetic field long before the inner core started to solidify about 1 billion years ago.

If the whole core was liquid back then, what kept the geodynamo alive? This has been one of the biggest gaps in Earth science. Scientists have struggled with this because most computer models couldn’t simulate a completely liquid core under realistic conditions. That’s where this new study changes the game.

The Breakthrough Model

The researchers developed a new computer model capable of simulating Earth’s core in conditions much closer to reality. Their simulations were so computationally demanding that they needed the Piz Daint supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano to run them.

What makes this study groundbreaking is that the team managed to minimize the influence of viscosity in their model. Viscosity refers to the internal resistance of a fluid to flow. In earlier models, viscosity had been artificially exaggerated because it’s difficult to simulate extremely low viscosities. But in Earth’s core, the viscosity is so small that its role should be negligible.

For the first time, the researchers demonstrated that when you simulate the core with realistic low viscosity, the geodynamo works just fine. This means that even a fully liquid Earth’s core could generate a magnetic field, in much the same way as today’s core does.

What the Findings Mean

By showing that viscosity doesn’t matter for the dynamo process under the correct conditions, the study answers the long-standing question of how Earth maintained its magnetic field in the distant past. It also confirms what geological data has been hinting at all along: a protective magnetic field existed billions of years ago, long before the inner core formed.

This has major implications:

It helps explain why life could emerge and survive billions of years ago. The shield was already in place, blocking harmful radiation.
It provides a new baseline for studying Earth’s magnetic history, giving geophysicists a clearer framework for interpreting ancient rock magnetism.
It offers insights into the magnetic fields of other planets and celestial bodies, such as Jupiter, Saturn, or even the Sun, where fluid dynamics play a dominant role.

Magnetic Field Changes Over Time

While the magnetic field has been around for billions of years, it’s not static. It has reversed polarity thousands of times, meaning the north and south poles have switched places. These reversals are recorded in rocks and are part of Earth’s natural history.

In recent decades, scientists have also observed the magnetic north pole drifting rapidly toward the geographic north pole. These changes matter because the field is vital for modern life too — from protecting satellites and astronauts to enabling technologies like GPS and telecommunications.

Understanding the deep history of the magnetic field helps us better predict its future behavior, which is crucial for our technological civilization.

Extra Knowledge: How We Study Ancient Magnetic Fields

Since we can’t directly observe the Earth’s core, scientists rely on indirect evidence:

Paleomagnetism: Some minerals in rocks lock in the direction and strength of the magnetic field at the time they formed. By studying ancient rocks, we can reconstruct the history of the field.
Meteorites: Studying magnetic signatures in meteorites gives hints about the cores of other planetary bodies.
Computer simulations: These allow scientists to test hypotheses about core dynamics under different physical conditions, as was done in this new study.

The results of this research not only fit with paleomagnetic evidence but also strengthen our confidence in how we interpret ancient data.

Other Planets and Magnetic Fields

Earth is not the only planet with a magnetic field. Jupiter and Saturn have extremely strong magnetic fields generated by different mechanisms involving metallic hydrogen. Mercury has a weak but still active dynamo. Venus, despite being similar to Earth in size, has almost no magnetic field — a mystery of its own.

This new study is significant because it suggests that solid inner cores aren’t always necessary for a dynamo to operate. That means exoplanets or other rocky worlds with fully liquid cores could still have protective magnetic fields, even without solidification. This expands our understanding of which planets might be habitable.

The Bigger Picture

The Earth’s magnetic field has always been a subject of both curiosity and necessity. On one hand, it’s a scientific puzzle — understanding it means diving into the complex physics of rotating fluids and electromagnetic forces. On the other hand, it’s deeply practical — our magnetic shield is essential for the survival of both natural life and modern technology.

By cracking this billion-year-old mystery, the ETH Zurich and SUSTech team have given us a clearer picture of our planet’s past and a sharper tool for predicting its future. Their model shows that the dynamo is remarkably robust, capable of running under conditions once thought inadequate.

The study doesn’t close the book on Earth’s magnetic mysteries — questions remain about how the inner core’s growth influenced field variations, or how mantle processes interact with the dynamo. But it does confirm one crucial point: the magnetic field has been around since the earliest chapters of Earth’s history, and it was strong enough to make our planet a safe harbor for life.