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While most of us take the ground beneath our feet for granted, written in its intricate layers, like the pages of a book, is the story of Earth. Our history.
Now, researchers have found more evidence of a whole new chapter deep within Earth’s past – Earth’s inner core appears to have another even more inner core.
“Traditionally, we’ve been taught that the Earth has four main layers: the crust, mantle, outer core, and inner core,” explained Joanne Stephenson, a geophysicist at Australian National University.
Our knowledge of what lies beneath the earth’s crust has been inferred primarily from what volcanoes disclosed and seismic waves whispered. From these indirect observations, scientists have calculated that the extremely hot inner core, with temperatures exceeding 5,000 degrees Celsius (9,000 Fahrenheit), is only one percent of the Earth’s total volume.
Now Stephenson and his colleagues have found more evidence that the Earth’s inner core could have two distinct layers.
“It’s very exciting – and it could mean we have to rewrite the manuals!” she added.
The team used a research algorithm to browse and match thousands of inner core models with decades-long observed data on how long seismic waves take to travel through Earth, collected by the International Seismological Center.
Differences in the paths of seismic waves through the layers of the Earth (Stephenson et al., Journal of Geophysical Research: Solid Earth, 2021)
So what is it over there? The team looked at some models of inner core anisotropy – how differences in the composition of its material alter the properties of seismic waves – and found that some were more likely than others.
While some models believe that the inner core material channels seismic waves faster parallel to the equator, others argue that mixing materials allows faster waves more parallel to the Earth’s axis of rotation. Even so, there are arguments about the exact degree of difference at certain angles.
This study failed to show much variation with depth in the inner core, but found that there was a change in the slow direction at an angle of 54 degrees, with the faster direction of the waves parallel. to the axis.
“We found evidence that could point to a change in the structure of iron, possibly suggesting two separate cooling events in Earth’s history,” Stephenson said.
“The details of this great event are still a bit of a mystery, but we have added another piece to the puzzle regarding our knowledge of the Earth’s inner core.”
These new findings may explain why some experimental evidence has been inconsistent with our current models of Earth’s structure.
The presence of an innermost layer has been suspected for some time now, with hints that the iron crystals that make up the inner core have different structural alignments.
“We are limited by the distribution of earthquakes and global receptors, especially at the polar antipodes,” the team wrote in their paper, explaining that the missing data decreases the certainty of their conclusions. But their 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 hopefully translate more stories written in this first layer of history. of the earth.
This research was published in the Geophysical Research Journal.
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