Apart from the thin crust on which we live, the structure of the Earth is intangible deep below our feet, so it is difficult to imagine.
Food often uses to show that the earth has four main layers, metaphors reminiscent of a tasty snack: graham crackers for the crust, ice cream for the mantle, melted marshmallows for the outer core, and chocolate chips for the inner core.
Scientists have long known about the fifth layer: a 400-mile-wide (650-kilometer) ball of metal in the inner core, aptly called the innermost core. Since its discovery in 2002, scientists have confirmed its existence many times, most recently in March 2022 however, since it hides beneath the various layers of the Earth and lies deep in the inner core of the planet – which itself is less than 1%. volume about the earth – the innermost core does not well understand.
Researchers studying the seismic waves generated by large earthquakes have now recorded the waves bouncing back and forth like a ping-pong ball along the Earth’s diameter five times – the highest bounce rate ever measured, beating the previous record of twice. Observing how these waves, created when Earth’s tectonic plates suddenly shift during earthquakes, distort as they travel through Earth’s center helps scientists focus more clearly on the elusive inner core.
The team behind the latest research studied the Earth’s core in an innovative way using three seismic data sets, each of which saw the core differently, study co-author Hrvoje Tkalčić told Space.com in an email. One of the events they investigated was the 7.9 magnitude earthquake that occurred in the Solomon Islands in 2017.
What Scientists Said
“Earth oscillates like a bell after a large earthquake, and not just for hours, but days,” Hrvoje Tkalčić, a geophysicist at the Australian National University and co-author of the latest study said in a statement.
To study the innermost core, scientists need seismometers located at the opposite ends of earthquakes at points they call antipodes, which are often in the ocean. Therefore, they have very little data due to the high cost of setting up seismic stations in such remote areas.
“The innermost inner core is notoriously difficult to probe by seismic waves,” Tkalčić told.
So the team combined seismic data from the Great Solomon Islands earthquake recorded at different data centers around the world and studied a seismic wave called the primary wave, pressure wave, or P-wave. The P-wave is the fastest of all seismic waves and the only one that passes through the center of the Earth, so studying it as it crossed the center of the Earth five times illuminated the planet’s deep interior.
Tkalčić’s team found that the wave crossed the width of the planet in 20 minutes. Each time, they clearly saw the “anisotropic” properties of the inner core: seismic waves passing through the innermost core slowed down in one direction, while those passing through the outer layer slowed down in another direction.
“It simply means that the iron crystals — iron, which is dominant in the inner core — are probably organized in a different way than in the outer shell of the inner core,” Tkalčić said in the same statement.
“Nature Communications” Journal
Scientists knew as early as 2003 that the innermost core is anisotropic, so the latest research confirms this knowledge with clearer evidence. In the new study, the researchers found that inside the inner core, the direction of P-waves is slowest at an “oblique” angle to the equatorial plane or 50 degrees from the Earth’s axis of rotation.
“This is critical, and this is why we can say we’ve detected ‘distinct’ anisotropy in the innermost inner core,” the authors wrote in a piece published by The Conversation.
There is strong evidence that slowly moving iron in the Earth’s core powers the planet’s geodynamo, leading to the formation of Earth’s global magnetic field. So understanding what happens in the center of the planet sheds light on how the magnetic field behaves and sometimes reverses.
While the latest study adds more evidence to confirm that the inner core is Earth’s fifth layer. It may take some time for the textbooks to update, Tkalčić told.
“After all, when the inner core was first hypothesized in 1936,” Tkalčić said, “it took some time for the model of the Earth to settle in and the textbooks to be changed.”
Soon after Earth’s innermost inner core makes its way to textbooks, food analogies will follow. Perhaps a dark chocolate center inside the chocolate chip?
The research describes in a paper published online on Feb. 21 in the journal Nature Communications.