A new analysis of the interior of the Earth has revealed that the inner core contains a dense iron ball at the center of our planet.
This may reveal some previously unknown details of the history of the formation and evolution of the Earth, pointing to an important global event at the beginning of the history of our planet.
The internal structure of the Earth consists of a series of concentric layers, from the earth’s crust to the core. At the center, with a radius of about 1,227 kilometers (762 miles), is the inner core, the densest part of our planet, a solid ball of mostly iron and nickel that makes up less than 1% of the Earth’s volume.
This inner core looks like a time capsule from Earth’s history.
As it grows, the solidification process releases heat and light, which causes convection in the outer liquid core, a motor that drives a dynamo that converts kinetic energy into magnetic energy and maintains the Earth’s global magnetic field. This magnetic field is believed to keep harmful radiation from the atmosphere and allow life to flourish.
Thus, changes in the inner core could lead to changes in the dynamo, which in turn could, over time, affect the Earth’s habitability.
But studying the inner core is not easy. We cannot slip in there and go deep into it; Instead, we must rely on seismic waves that bounce off the planet’s interior and change when they encounter sizes of different densities.
More than 20 years ago, scientists identified the existence of another inner core within the inner core. They called it the innermost inner core, and other studies have confirmed its existence. But learning more about them has been difficult, partly because they are hidden by many other layers, and partly because placing seismic stations in the right places can be difficult.
However, the number of global seismic monitoring stations around the world continues to grow, constantly recording the subtle shaking of the planet under our feet. Now, seismologists Thanh Son Phum and Hrvoe Tkalich at the Australian National University (ANU) have come up with a way to extract data from the innermost core from these records.
In their article, they wrote: “This study uses an ever-expanding global network of seismographs to create global ensembles of some individual important seismic events. This study belongs to a previously unobserved and untapped class of aftershock seismic observations over much of the Earth along, as far as we know, even in five times its diameter, bounces of more than two syllables have not yet been reported in the seismological literature.”
When a giant earthquake hits the Earth, this event creates ripples that spread throughout the planet, passing through and bouncing off internal structures. And that’s how scientists got such a detailed map of what’s inside the Earth.
But when the seismic waves reach the boundary, the wave that bounces back—bounces back like an “echo” of an earthquake—becomes much weaker. Previously, scientists have reported no more than two passages of a seismic event around the planet.
By stacking the data—combining a group of seismic signals into a single trace—Fomm and Tkalich were able to amplify the signal from several large seismic events, thereby breaking this record. For the first time, they identified triple, quadruple, and five-fold seismic bounces, which in turn allowed for a more detailed study of the inner core than previously achieved.
The varying travel times of the wave pairs indicated the presence of an innermost core no larger than 650 kilometers (404 miles) in diameter, composed of dense iron. This structure could be the result of a fundamental change in the growth of the inner core at some point in the Earth’s past.
The study means, the researchers say, that we now have sufficient evidence for the existence of the innermost inner core, and that future efforts should focus on characterizing it, the outer inner core, and the boundary between them.
The results are reported by Nature Communications.
Source: Science Alert
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