How has the Earth’s magnetic field changed in the course of our planet’s history? How was it during the early stages? Why did this magnetic shield appear almost immediately after the formation of the Earth? These are the questions posed by some researchers at the University of Rochester who have published a scientific study on PNAS, a study that could also prove very important for understanding the future evolution of the Earth itself and similar planets.

The researchers came to the conclusion that the Earth’s magnetic field was even stronger during the early stages of Earth’s history than it is today. The magnetic shield that we see today owes its origin to the Earth’s outer core (the outermost part of the inner core) thanks to the immense heat of the Earth’s interior that makes the outer core itself swirl and shake. The latter, being composed of liquid iron, generates electric currents, currents that feed the Earth’s own magnetic field.

However, shortly after the formation of the Earth, things worked a little differently, according to this study. By analyzing with new techniques some samples of zirconium crystals, the oldest known terrestrial materials, researchers have obtained important information about the formation of the Earth’s magnetic field.

The analysis suggests the existence of a stronger magnetic field than previously calculated about 4 billion years ago. At that time, however, this field had to be powered by a different mechanism because the inner core has not yet formed (the inner core should have formed only 565 million years ago, according to another study).

According to the researchers, this mechanism is represented by the chemical precipitation of magnesium oxide inside the Earth, as explained by John Tarduno, professor of environmental earth sciences and one of the authors of the study. This magnesium oxide must have dissolved due to the immense heat caused in turn by the impact of the Earth with a very large body, which then led to the formation of the Moon.

As the Earth’s interior cooled, the magnesium oxide “precipitated” providing the mechanism needed to “feed” the Earth’s first magnetic field. Just about 565 million years ago, magnesium oxide would begin to wear out and the magnetic field would consequently begin to disappear.
But, according to the researchers, just in this period the inner core was forming, which provided a new source of power and allowed the magnetic shield that surrounds our planet to continue to exist.