Earth's magnetic field is more than 4 billion years old

Laila Ali

Using zircon stones, the oldest minerals on Earth, scientists have found that the Earth’s magnetic field is more than four billion years old, roughly the age of the Earth, and new research from the University of Rochester provides evidence that the magnetic field that first formed around the Earth was stronger Than scientists previously thought.

The research, published in PNAS, on January 21, 2020, will help scientists draw conclusions about the sustainability of Earth's magnetic shield, and whether there are other planets in the Solar System that have the conditions to harbor life on them.

"This research tells us about what constitutes a viable planet," said John Tardono, research associate and professor of earth and environmental sciences at the University of Rochester.

Determining the age of the Earth's magnetic field is extremely important to understanding the evolution of the planet, because the field protects the atmosphere from the solar wind.

The absence or presence of the geomagnetic field also provides a unique measure of early basic conditions of life formation.

Evidence for a 4.2 billion year old geomagnetic field comes from ancient magnetic analyzes of the zircon stone.

Magnetic field today and past
Today the Earth's magnetic shield is generated in the outer core of the Earth, where the intense heat in the Earth's dense inner core causes the outer layer, made up of liquid iron, to move a spiral and fluctuations, and to generate electrical currents, to generate a phenomenon called geodynamo that occupies the Earth's magnetic field.

The currents in the liquid outer core are strongly affected by the heat flowing from the solid inner core. Because of the location and the extreme temperatures of the materials in the Earth's core, scientists cannot directly measure the magnetic field.

Fortunately, the minerals that rise to the surface of the earth contain small magnetic particles that indicate the direction and intensity of the magnetic field.

Using new optical magnetic data, an electron microscope, and geochemical data, the researchers dated and analyzed the zircon crystals, the oldest minerals on earth, collected from locations in Australia.

Zircon, which is about a tenth of a millimeter, contains smaller magnetic particles that indicate the magnetization of the Earth at the time of the formation of the zircon.

And research by Tardono found that the Earth's magnetic field is at least 4.2 billion years old, and thus has been around for nearly the beginning of the age of the planet.

On the other hand, however, the Earth's inner core is relatively recent, forming only about 565 million years ago, according to research published by Tardoneau and his colleagues earlier this year.

Precipitation of magnesium oxide
While researchers initially believed that the Earth's early magnetic field was weak, new zircon data indicated that it was a strong magnetic field.

But given that the inner core had not yet formed, the strong field - which originally originated four billion years ago - must be supported by another mechanism that powers it.

"We think this mechanism is the chemical precipitation of magnesium oxide inside the Earth," says Tardonu. It is possible that the dissolution of magnesium oxide was due to the influence of the intense heat caused by the formation of the Earth's moon. Also, during the geothermal phase, magnesium oxide can be oxidized, thereby stimulating the thermal transfer process and geodynamo.

The researchers believe that the Earth's interior eventually exhausted the source of magnesium oxide to the point that the magnetic field had almost completely collapsed 565 million years ago.

But the formation of the Earth's inner core has provided a new source of Earth's dynamic operation and the planetary magnetic shield of Earth today.

The collapse of the magnetic shield of Mars
"The Earth's early magnetic field was extremely important because it was protecting the atmosphere and preserving Earth's water when the solar wind was more intense," Tardono says.

He adds, "The magnetic field generation mechanism is almost certainly very important to study other planets and planets outside our solar system." It is known that the leading theory, regarding Mars, that it was like planet Earth, has an early magnetic field. However, the field collapsed, and Mars did not generate a new field opposite the Earth.

"Once Mars lost its magnetic shield, it lost its water. But we still do not know the cause of the collapse of the magnetic shield. So we are interested in the sustainability of the magnetic field. This study provides us with more data in an attempt to know the set of factors that have preserved the magnetic shield of the planet ".