Earth’s inner core may be more complex than researchers thought

There may be a secret chamber in the heart of the Earth. Researchers say the planet’s inner core is not just a solid ball of nickel and iron, but contains two layers of its own: a separate central region located inside the outer shell. Scientists say they have confirmed the existence of this innermost inner core using a type of previously undescribed seismic wave that not only passes through the Earth’s core but also bounces back and forth inside, gathering invaluable data about the structure of the core.Focusing on earthquakes of magnitude 6 or greater that have occurred in the past decade, researchers o combined data on these earthquakes collected at seismic stations around the world. Combining these signals made it possible to detect even very weak reflections of seismic waves. Of the approximately 200 earthquakes analyzed, 16 events produced seismic waves that visibly reflected through the inner core multiple times. The origin, structure, and fate of the Earth’s core is of great interest because the core generates the planet’s magnetic field, which protects the Earth from charged particles that emitted by the Sun, and helps to protect the inhabitants of the planet from excessive radiation. kilometers, consists of two main parts: a liquid outer core and a solid inner core. As the iron-rich liquid circulates in the outer core, some of the material cools and crystallizes, sinking to form a solid center. This interaction creates the Earth’s magnetic field. It is not known when this whirling dance first began, but some studies suggest that it happened 565 million years ago, which is only a fraction of the Earth’s 4.6 billion year lifespan. This dance was delayed from time to time, its stuttering steps preserved in tiny magnetic grains in the rocks. These data suggest that the planet’s magnetic poles have reversed many times over the years, temporarily weakening the magnetic field. As more and more crystals cool, the dance will eventually slow down and stop, turning off the planet’s magnetic field after millions or billions of years. Different types and structures of minerals, as well as different amounts of fluids in the subsurface, can change the speed of seismic waves that travel through Earth. , offering clues to the composition of the subsoil. In 2002, researchers noted that seismic waves passing through the deepest part of the Earth move a little slower in one direction relative to the poles of the planet than in other directions. This suggests that there is some oddity here—perhaps a difference in crystal structure. The team hypothesized that this hidden heart might be a fossil of sorts: a long-preserved remnant of early core formation. Following this observation, Tkalcic and others examined seismic data, finding independent lines of evidence that help support the idea of ​​an innermost core. Reverberation seismic waves, described on February 21 in Nature Communications , also show deceleration and are the strongest evidence that this hidden heart exists. Using this seismic data, Tkalcic and seismologist Thanh-Song Pham, also of the Australian National University, estimated that this inner heart is about 600 kilometers across, or about half the diameter of the full inner core. And the pair was able to estimate the direction of the slowest waves by about 50 degrees relative to the Earth’s axis of rotation, providing a better understanding of the region. Tkalcic says the exact source of the slowing of the waves is unknown. This phenomenon may be related to the structure of the iron crystals, which may be packed together differently further into the center. Or it could be due to a different crystal alignment caused by some ancient global event that changed the way the inner core crystals hardened from the outer core. The inner core also holds many other secrets. Lighter elements present in small quantities in the core – hydrogen, carbon, oxygen – can flow around solid iron in a liquid “superionic” state, further complicating the seismic picture. Having discovered seismic waves that repeatedly reflected inside the planet, researchers made an invaluable contribution, which will help researchers study the core in new ways, says seismologist Paul Richards of Columbia University’s Lamont-Dougherty Observatory in Palisades. , New York However, the team’s interpretation of the structure of the inner core from these waves is “probably more questionable,” 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 become weaker and harder to see in the data, he says. “Many further observations will help decide” what this new data might reveal about the planet’s heart.