Scientists have discovered signs of a hidden structure within the Earth’s core: ScienceAlert

While most of us take the land beneath our feet for granted, the history written within its complex layers, like the pages of a book, is the history of the Earth. Our history.

Research shows that there are unknown chapters in that history, deep in Earth’s past. In fact, the Earth’s inner core appears to contain another, larger inner core.

“We’ve traditionally been taught that the Earth has four main layers: the crust, the mantle, the outer core, and the inner core,” says Australian National University geophysicist Joan Stevenson. He explained in 2021.

Our knowledge of what lies beneath the Earth’s crust has been mostly deduced from what volcanoes have revealed and what seismic waves have whispered.

From these indirect observations, scientists calculated that the extremely hot inner core, with temperatures exceeding 5,000 degrees Celsius (9,000 degrees Fahrenheit), makes up only 1% of the Earth’s total volume.

But a few years ago, Stevenson and his colleagues found evidence that the Earth’s inner core may actually contain two distinct layers.

“It’s very exciting – and it may mean we have to rewrite the textbooks!” Stevenson explained at the time.

The team used a search algorithm to search for thousands of models of the inner core and match them with observed data over many decades on how long it takes seismic waves to travel through the Earth, collected by the International Seismological Center.

Differences in the paths of seismic waves across the Earth’s layers. (Stevenson et al.Journal of Geophysical Research: Solid Earth, 2021)

So what’s there? The team looked at some models of the inner core contrast – How do differences in the composition of matter change the properties of seismic waves – and some were found to be more likely than others.

While some models suggest that the material of the inner core channels faster seismic waves parallel to the equator, other models suggest that the mixture of materials allows for faster waves more parallel to the Earth’s rotation axis. Even then, there are arguments about the exact degree of difference at certain angles.

The study here did not show a significant difference in depth in the inner core, but did find that there was a change in the slow direction to an angle of 54 degrees, with the faster direction of the waves parallel to the axis.

“We have found evidence that may indicate a change in the structure of iron, possibly indicating two separate cooling events in Earth’s history,” Stevenson said. He said.

“The details of this major event are still a bit hazy, but we have added another piece to the puzzle when it comes to our knowledge of the Earth’s inner core.”

These results may explain why Some experimental evidence It was not consistent with our current models of Earth’s structure.

The existence of an inner 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 their receptors, especially at the poles.” The team wrote In their research, explaining missing data reduces the certainty of their conclusions.

But their conclusions are consistent with other studies on the anisotropy of the deeper inner core.

Future research may fill some of these data gaps and allow scientists to confirm or refute their findings, and hopefully translate more stories written within this early layer of Earth’s history.

This research was published in Journal of Geophysical Research.

A previous version of this article was published in March 2021.