Earth: according to scientists it has a fifth metallic layer never discovered so far

Crust, mantle and, deeper down, the heart of the Earth which we know to be divided into two layers: a molten outer core and a solid and metallic inner core, composed of iron and nickel. So far, no doubts. At least until now, because textbooks could be rewritten. According to some researchers of the Australian National University (Anu), in fact, there would actually be a fifth layer terrestrial. Specifically, it is one metal ball 650 kilometers thick at the center of the inner core, a real gateway to the past that will be able to tell us more about the evolution of our planet. “The existence of a metallic sphere inside the inner core was hypothesized about 20 years ago”explains Thanh-Son Phạm, one of the signatories of the paper just posted on Nature Communications. “We now provide another set of evidence to prove this hypothesis.”

The beginning

Starting from the data of about 200 powerful earthquakes (magnitude 6 or greater) recorded in the last decade, researchers have focused on seismic waves, which are usually used as a tool to understand and study the earth’s composition. In fact, these vibrations behave a bit like a ping pong ball bouncing back and forth: they travel directly through the different layers and the center of the Earth and reappear on the opposite side of the globe from where the earthquake was triggered, i.e. L’antipode. The waves then go back to the origin of the earthquake. In this way, therefore, it is possible to have information on how the Earth is structured and composed.

“By developing innovative techniques to amplify the signals recorded by seismographic networks, we have observed for the first time seismic waves bouncing back and forth up to five times along the diameter of the Earth”comments Pham. “Previous studies have documented only one antipode bounce”. From here, therefore, the researchers were able to study theanisotropy of the nickel iron alloy that characterizes the inner core of the Earth. Anisotropy, we recall, is a property by which in a substance the value of a physical quantity, whether it is speed, refractive index or accretion, depends on the direction being considered. In this case, therefore, it serves to describe how the seismic waves they speed up or slow down through a material depending on the direction they travel.

The deduction

Therefore, changes that could be caused by the different arrangement of the atoms of iron at high temperatures and pressures or from the alignment of crystals within the Earth’s core. By analyzing the variation of the travel times of the seismic waves, in fact, the researchers were able to deduce that the structure of the innermost region of the inner core it is probably different from the external one. That’s why the waves speed up or slow down depending on their angle of entry as they penetrate the innermost core. “It simply means that the iron crystals are probably organized differently than the outside of the inner core”, they specify the authors.

The findings also suggest that a important event during the’evolution of the Earth which has led to a significant change in the crystalline structure of the inner core. “This inner core is like a time capsule of Earth’s evolutionary history and serves as a gateway to events in our planet’s past. Events that occurred on Earth hundreds of millions to billions of years ago”concluded Hrvoje Tkalčić, ANU seismologist. “There are still many unanswered questions about the innermost core that may hold the secrets to piece together the mystery of training of our planet”.