Earth's history is recorded inside its various layers, much like the pages of a book. However, there are little-known chapters in that history, deep within Earth's past, according to research. In fact, Earth's inner core looks to include an additional inner core.
Joanne Stephenson, a geophysicist at the Australian National University, explained in 2021 that Earth's layers are only composed of four primary layers, namely the crust, mantle, outer, and inner core. But, Stephenson and colleagues discovered evidence that Earth's inner core may contain two separate layers a few years ago.
Discovering Earth's Fifth Layer
The common understanding of what lies under the Earth's crust is primarily based on what volcanoes have revealed and seismic waves have murmured. Based on these indirect measurements, scientists concluded that the scorchingly hot inner core, with temperatures exceeding 5,000 degrees Celsius (9,000 degrees Fahrenheit), accounts for just 1% of Earth's total volume.
As part of the study, MailOnline reported that researchers examined journey time data from the International Seismological Center for seismic waves traveling inside the Earth.
Then, they used a search algorithm to go through and compare hundreds of inner core models with data they obtained over many decades regarding how long seismic waves take to travel through Earth.
Identifying these microscopic variations in iron structure proved especially tough, but scientists were able to establish two distinct cooling periods in Earth's history.
This shows that a huge and hitherto unknown catastrophe occurred during the early years of Earth's history, maybe as long as 4.5 billion years ago. Stephenson explained that the intricacies of this massive event remain a mystery, but they have added another piece to that jigsaw puzzle in terms of understanding the Earth's inner core.
Scientists discovered changes in the structure of iron within the inner core, implying a new 'border line' running around 650 kilometers from the center of the Earth. Stephenson, the study's lead author, said that finding it was extremely exciting and that it may cause some revisions in textbooks.
What's Inside the Innermost Inner Core?
As per Science Alert, the researchers examined different models of the inner core's anisotropy, which explains how changes in the composition of its material influence the qualities of seismic waves, and discovered that some were more plausible than others.
Unlike some theories that imply that the inner core's material channels seismic waves quicker parallel to the equator, others propose that the material mix allows for faster waves parallel to the Earth's rotating axis. Still, there are disagreements on the precise degree of difference at certain angles.
The study, titled "Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm" published in the Journal of Geophysical Research, found that the sluggish direction of waves changed to a 54-degree angle increasing depth in the inner core, with the quicker direction of waves flowing parallel to the axis.
These new discoveries might explain why certain experimental data have been discordant with the existing understanding of Earth's structure. The possibility of an innermost layer has previously been postulated, with clues suggesting the inner core's iron crystals have unusual structural alignments.
The team explained that scientists are constrained by the distribution of earthquakes worldwide. But their conclusions align with other research on the anisotropy of the innermost inner core. They hope future studies would be able to translate more of Earth's history.
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