New evidence shows Earth’s magnetic field is at least 3.7 billion years old

The oldest clear evidence for Earth’s magnetic field suggests that it was formed within the first billion years of Earth’s existence. The new discovery brings us closer to answering the important question of whether Earth’s magnetic field can be traced back to its formation, and if not, how long ago it emerged.

The magnetic field that surrounds the Earth and partially protects us from solar radiation is thought to be crucial to the formation and survival of life. Although we know that giant planets like Jupiter can have strong magnetic fields, there is much debate over how common magnetic fields are on rocky planets. If there are few or generally weak planet-wide magnetic fields, it may limit the widespread emergence of life in the galaxy, or at least the emergence of advanced life.

This makes exploring the origins of Earth’s magnetic field a top priority for many geologists, but it’s not an easy question to answer. Rocks can retain evidence of the magnetic fields they formed, but this evidence can be lost or altered if they become hot enough to rearrange the iron particles within them. Now, however, clues have been found in some of the oldest unaltered rocks on Earth.

The Isua Crust Belt represents the earliest continental crustal material to form, and parts of it have survived relatively untouched by geological processes since then. Unfortunately for geologists, its location in West Greenland is one of the most difficult places on Earth to conduct field research.

Like many young iron-rich rocks, the banded iron formations in the Isua Belt reveal the direction and, to some extent, the strength of the magnetic fields they form. The magnetite particles align in the direction of the magnetic field, like the iron filings surrounding a modern bar magnet. Lead author Claire Nichols, a professor at the University of Oxford, believes these are original and not later oriented during cooling from a heat event.

“Extracting reliable records from such ancient rocks is extremely challenging, and it was fascinating to see the raw magnetic signals begin to emerge as we analyzed these samples in the lab,” Nichols said in an emailed statement to IFLScience. People are excited. This is a very important step as we try to determine the role of ancient magnetic fields when life first emerged on Earth.

The age of Earth’s magnetic field is still questioned, in part because we don’t fully understand what causes it today. We know it is the product of the motion of the molten outer core, whose high iron content turns electrical currents into electrical currents generated by the solidification of the inner core.

However, there are enough uncertain details that we cannot be confident that this motion occurred before the solid core formed. The rocks Nichols and colleagues studied suggest they did, because the core is almost certainly much younger, probably more recent than multicellular life. The findings have important implications for how much heat escaped from Earth’s core in its early days, driving upwellings in the mantle and fueling volcanic activity.

The northeastern part of the Isua Belt is unusual and perhaps unique for rocks of this age in that it lies above a continental crust thick enough to protect it from those activities that heat many of its other counterparts. Nichols and co-authors concluded that the fragment they studied reached 550 degrees Celsius (980 degrees Fahrenheit) during its formation 3.69 billion years ago but has never exceeded 380 degrees Celsius (720 degrees Fahrenheit) since then, making The arrangement of magnetic particles is primitive.

The research is published in the Journal of Geophysical Research: Solid Earth.