There Could Be a Whole Other Core Inside Earth’s Inner Core

There may be a secret chamber in the heart of the Earth. Researchers say the planet’s inner core isn’t just a solid ball of nickel and iron, but has two layers of its own: a distinct central region housed within an outer shell.

Scientists Say They’ve Confirmed existence of this innermost core Using a type of previously undescribed seismic wave that not only travels through Earth’s core but also bounces back and forth through the interior, collecting invaluable data about the core’s composition along the way.

Focusing on earthquakes of magnitude 6 or greater that occurred in the past decade, the researchers pooled data on these earthquakes that were collected at seismic stations around the world. The combination of these signals made it possible to detect even very faint reflections of seismic waves. Of the 200 or so earthquakes analyzed, 16 events produced seismic waves that, at times, apparently bounced through the inner core.

The origin, composition, and fate of Earth’s core is of intense interest because the core generates the planet’s magnetic field, which protects Earth from charged particles emitted by the Sun and helps protect the planet’s inhabitants from too much radiation. .

“Understanding how the magnetic field evolves is extremely important for life on Earth’s surface,” says Hervoje Talkic, a seismologist at the Australian National University in Canberra.

The entire core of approximately 6,600 km consists of two main parts: a liquid outer core and a solid inner core ,Sn: 1/23/23, As the iron-rich fluid seeps into the outer core, some of the material cools and crystallizes, sinking to form a solid center. That interplay generates Earth’s magnetic field.

It is not certain when this whirling dance first began, but some studies suggest that it was more recent. 565 million years agoonly a fraction of Earth’s 4.6 billion year long lifetime (Sn: 1/28/19, That dance has wobbled from time to time, its wobbly steps preserved in tiny magnetic grains in the rocks. These figures suggest the planet’s magnetic poles have reversed Several times over the years, a temporary weakening of the magnetic field (Sn: 2/18/21, As more and more crystals cool, the dance will eventually slow and stop, shutting down the planet’s magnetic field millions or even billions of years from now.

Different types and compositions of minerals, as well as different amounts of liquid in the subsurface, can change the speed of seismic waves traveling through the Earth, providing clues to the makeup of the interior. In 2002, researchers observed that seismic waves pass through the innermost part of the Earth go slow in one direction relative to the poles of the planet than in other directions. This suggests that there is some asymmetry there – differences in crystal structure, perhaps. That hidden heart, the team suggested, may be a fossil of sorts: a long-preserved relic of the core’s early formation.

Since that observation, Tkalčić and others have looked into seismic data, finding independent lines of evidence that help support the idea of ​​an innermost inner core. Resonant seismic waves, described on February 21 nature communicationThe recession also shows up, and is the strongest evidence yet that this hidden heart exists.

Using that seismic data, Tkalčić and seismologist Thanh-Song Phạm, also of the Australian National University, estimate that this inner heart is about 600 kilometers across, or about half the diameter of the full inner core. And the pair were able to estimate the direction of the slowest waves at about 50 degrees relative to Earth’s rotation axis, providing more information in this area.

The exact source of wave deceleration is unclear, says Tkalčić. The phenomenon may be related to the structure of the iron crystals, which can be packed together far apart in the centre. Or it could result from a different crystal alignment due to some long-ago global event that changed how the inner core crystals from the outer core.

The inner core holds many more secrets. Lighter elements present in smaller amounts in the core – hydrogen, carbon, oxygen – A liquid can flow around solid iron in a “superionic” stateFurther complicating the seismic picture (Sn: 2/9/22,

By identifying and reporting the seismic waves that bounce back and forth many times through the planet’s interior, researchers have made an invaluable contribution that will help researchers understand what is happening, says Paul Richards, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades. Will help to study the core in new ways. , NY

Still, the team’s interpretation of the inner core’s structure from those waves “is probably more iffy,” says Richards, who was not involved in the work.

One reason for this uncertainty is that as the waves bounce back and forth, they can weaken and be difficult to see in the data, he says. “Many further observations will help to decide” what these new data can reveal about the planet’s heart.