Researchers trying to uncover the secrets of Earth’s geology have revealed the fifth layer of the planet. Seismic waves generated by earthquakes have revealed new insights about the deepest parts of Earth’s inner core.
The team of researchers from the Australian National University measured the speeds at which these seismic waves penetrate and pass through the Earth’s inner core. The team believes that this has presented evidence of a distinct layer inside Earth known as the innermost inner core.
The researchers analysed data from about 200 magnitude-6 and above earthquakes from the last decade.
This layer is a solid ‘metallic ball’ that sits within the center of the inner core. The findings of the study have been published in the journal Nature Communications, which states that probing the Earth’s center is critical for understanding planetary formation and evolution.
“The existence of an internal metallic ball within the inner core, the innermost inner core, was hypothesised about 20 years ago. We now provide another line of evidence to prove the hypothesis,” Dr. Thanh-Son Phạm, from the ANU Research School of Earth Sciences, said.
So far, four layers of Earth’s structure had been identified. This includes – the crust, mantle, outer core, and inner core. The new findings indicate a fifth layer beneath that.
The team assessed the seismic waves that travel directly through the Earth’s center and ‘spit out’ at the opposite side of the globe to where the earthquake was triggered. The waves then travel back to the source of the quake. The team studied the earthquake, which originated in Alaska. The waves bounced off somewhere in the south Atlantic Ocean, before traveling back to Alaska.
“By stacking waveforms recorded by a growing number of global seismic stations, we observe up-to-fivefold reverberating waves from selected earthquakes along the Earth’s diameter,” the paper read.
The researchers studied the anisotropy of the iron-nickel alloy that comprises the inside of the Earth’s inner core. Anisotropy is used to describe how seismic waves speed up or slow down through the material of the Earth’s inner core, depending on the direction in which they travel. They found that bouncing seismic waves repeatedly probed spots near the Earth’s center from different angles.
The team analysed the variation of travel times of seismic waves for different earthquakes. They found that crystallised structure within the inner core’s innermost region is likely different from the outer layer. The team suspects that there could have been a major global event at some point during Earth’s evolutionary timeline that led to a “significant” change in the crystal structure of the inner core.
