The Earth is the only planet in the universe that we know for sure supports life. While it is likely that many others do, it is almost certain that most planets do not have life for one reason or another. One important factor that allows the Earth to be such a great place for life is that it has a built-in shield to protect it from cosmic radiation.

That shield is a magnetic field that is generated thanks to the outer core of the planet, which is made of molten iron and nickel. Those molten metals are conductive, and since they are always in motion (thanks to the planet’s rotation and convection), a large electric current is created, which in turn generates the massive magnetic field around our planet.

But just how long has this electromagnetic field been around the Earth? Well, there is a lot of debate about that. Virtually all experts today agree that it goes back at least 3.7 billion years. A 2025 study conducted at the University of Oxford looked at iron-rich rocks that were discovered in Greenland.

Found in a location known as the Isua Greenstone Belt, these rocks have iron particles embedded in them that act as tiny magnets. These magnets record both the direction of the magnetic field at the time they formed and its strength. The study showed that when they formed 3.7 billion years ago, the magnetic field around the Earth was around 15 microteslas.

The magnetic field today is 30 microteslas, for comparison.

Other experts believe that the magnetic field is even older, though that is much more disputed. A 2015 study looked at zircon crystals to determine the magnetic field at the time of their creation. Based on this study, it is possible that the magnetic field goes back 4.2 billion years. Another study in 2020, however, found that these crystals had melted and reformed since then, making dating using them unreliable.

Whatever the exact time when the magnetic field started, it is a good thing that it did. Life first emerged around 3.7 billion years ago, which lines up with the approximate time when the magnetic field came about (according to the 2025 study). If these two events are closely correlated, it would help to show that a magnetic field protecting a planet from cosmic radiation may be an important factor when it comes to the evolution of life.

Whenever it started, I’m just glad it is here today.

If you thought that was interesting, you might like to read about the mysterious “pyramids” discovered in Antarctica. What are they?