Research has shown that there are unknown chapters in the history of the depths of the Earth, and it seems that the inner core of the Earth contains another inner core inside it.
Geophysicist at the Australian National University Joanne Stephenson said: “We have traditionally known that the Earth consists of four main layers: the crust, the core (the outer and inner mantle or mantle) and the core. ".
And she added: Through these indirect observations, scientists have concluded that the extremely hot inner core, with temperatures exceeding 5,000 degrees Celsius (9,000 Fahrenheit), constitutes only 1% of the total volume of the Earth. But a few years ago, researchers found evidence that Earth's inner core may, in fact, have two distinct layers.
"It's very exciting, and it might mean we have to rewrite the textbooks!" Stephenson said.
The team used an algorithm to search through thousands of models of the inner core and matched it against decades of observational data about how long seismic waves take to travel through the Earth, collected by the International Seismological Center.
So what's down there?
The team looked at some models of inner core anisotropy, how differences in the composition of its matter change the properties of seismic waves, and found that some were more likely than others.
While some models suggest that the material of the inner core channels faster seismic waves parallel to the equator, others suggest that the mixture of materials allows for faster waves more parallel to the Earth's axis of rotation. Even so, there are arguments about the exact degree of divergence at certain angles.
The study here did not show a significant variation with depth in the inner core, but found that there was a slow change in direction to an angle of 54 degrees, with a faster direction of the waves running parallel to the axis.
"We found evidence that may indicate a change in the structure of iron, indicating perhaps two separate cooling events in Earth's history," Stephenson said, noting that "the details of this major event are still a bit fuzzy, but we added another piece of the puzzle when it came to knowledge of the inner core of the Earth.
These new findings may explain why some of the experimental evidence is inconsistent with our current models of Earth's structure.
A deeper layer has been suspected before, with hints that the iron crystals that make up the inner core have a different structural alignment.
"We are limited by the distribution of global earthquakes and receivers, especially in the antipolar," the team wrote in their paper, explaining that the missing data reduce the certainty of their conclusions.
But their conclusions are in line with other studies of anisotropy in the innermost inner core.
Future research may fill in some of these data gaps, allow scientists to corroborate or contradict their findings, and hopefully translate more of the stories written within this early layer of Earth's history.