Introducing Earth's inner inner core

by Julia Rosen
Tuesday, June 16, 2015

A humongous hunk of iron — that’s how scientists have long thought of Earth’s solid inner core. But new research suggests there’s more to it than that: namely, that the inner part of the inner core may have different physical properties than the outer part. In addition to revealing a new feature in Earth’s layer-cake internal structure, the discovery may shed light on the planet’s formation, say the authors of the study, published in Nature Geoscience.

Clues hinting at the existence of this inner inner core emerged from 20 years' worth of seismic data recorded at almost 1,800 monitoring stations scattered around the world. Instead of looking at the shock waves produced directly by earthquakes, however, the scientists used the seismic echoes that reverberate inside the planet after a temblor occurs. This allowed them to study the structure of Earth’s interior in greater detail than ever before.

They noticed that the travel times of seismic waves traversing Earth’s inner core differed around the planet. The researchers, led by Xiaodong Song of the University of Illinois at Urbana-Champaign and Tao Wang of Nanjing University in China, suggested that their observations could be explained if the iron crystals in the inner inner core had a preferred east-west orientation, allowing equatorial waves to move faster in this direction. Iron crystals in the outer inner core, meanwhile, have a well-known north-south alignment.

The authors speculated that something may have happened during the formation of the core that shifted its crystal orientation, although at present, they don’t know just what.

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