While most of us take for granted the earth beneath our feet, the history of the Earth is written within its complex layers, like the pages of a book. Our history.
Researchers have now found more evidence of a completely new chapter in the Earth’s past: the Earth’s inner core seems to have another even more inner core.
“We have traditionally been taught that the Earth has four main layers: the crust, the mantle, the outer core and the inner core,” explained Joanne Stephenson, a geophysicist at the National University of Australia.
Our knowledge of what lies beneath the Earth’s crust has been deduced primarily from what volcanoes have reported and seismic waves whispered. From these indirect observations, scientists have calculated that the very hot inner core, with temperatures exceeding 5,000 degrees Celsius (9,000 Fahrenheit), represents only 1% of the total volume of the Earth.
Now Stephenson and his colleagues have found more evidence that the inner core of the Earth can have two different layers.
“It’s very exciting and it can mean we have to rewrite textbooks.” added.
The team used a search algorithm to drag and match thousands of models of the inner core with data observed over many decades about the time it takes seismic waves to traverse the Earth, collected by the International Seismological Center.
Differences in the paths of seismic waves through layers of the Earth. (Stephenson et al., Journal of Geophysical Research: Solid Earth, 2021)
So what’s down there? The team examined some models of inner core anisotropy (such as differences in the composition of its material altering the properties of seismic waves) and found that some were more likely than others.
While some models think that the material in the inner core channels seismic waves faster parallel to the equator, others argue that mixing materials allows faster waves more parallel to the axis of rotation. the earth. Even then, there are arguments about the exact degree of difference at certain angles.
This study did not show many variations with respect to the depth of the inner core, but found that there was a change in the slow direction at a 54-degree angle, with the fastest direction of the waves parallel to the axis.
“We have found evidence that may indicate a change in the structure of iron, suggesting perhaps two separate cooling events in Earth’s history,” Stephenson said.
“The details of this great event are still a bit mysterious, but we’ve added another piece of the puzzle in terms of knowledge of the inner core of the Earth.”
These new findings may explain why some experimental tests have been incompatible with our current models of Earth’s structure.
The presence of a deeper layer has long been suspected, with indications that the iron crystals that make up the inner core have different structural alignments.
“We are limited by the distribution of earthquakes and global receivers, especially at polar antipodes,” the team wrote in its paper, explaining that the missing data diminishes the certainty of its findings. But its findings align with other recent studies on the anisotropy of the innermost inner core.
A new method currently in development may soon fill some of these data gaps and allow scientists to corroborate or contradict their findings and we hope to translate more stories written within this first layer of Earth’s history.
This research was published in Journal of Geophysical Research.