Earth's Inner Core Has a Suprising Inner Core of Its Own

Most people know that our planet Earth has a core; but did you know that the core has a core? Seismic waves are helping scientists plumb the depths of our planet and have shown that the Earth actually has an inner core.

"Even though the inner core is small-smaller than the moon-it has some really interesting features," said Xiadong Song, one of the researchers, in a news release. "It may tell us about how our planet formed, its history, and other dynamic processes of the Earth. It shapes our understanding of what's going on deep inside the Earth."

In order to get a better glimpse of the Earth's core, the researchers used seismic waves from earthquakes to scan below the planet's surface. This is a bit like how doctors use ultrasound to see inside patients. More specifically, the researchers used technology that gathers data not from the initial shock of an earthquake, but from the waves that resonate in the earthquake's aftermath.

"It turns out the coherent signal enhanced by the technology is clearer than the ring itself," said Song. "The basic idea of the method has been around for a while, and people have used it for other kinds of studies near the surface. But we are looking all the way through the center of the Earth."

The researchers actually discovered that the inner core has some complex structural properties. It has an inner-inner core that's about half the diameter of the whole inner core. The iron crystals in the outer layer of the inner core are aligned directionally, north-south. However, the inner-inner core may be made up of a different kind of crystal, or a different phase.

"The fact that we have two regions that are distinctly different may tell us something about how the inner core has been evolving," said Song. "For example, over the history of the Earth, the inner core might have had a very dramatic change in its deformation regime. It might hold the key to how the planet has evolved. We are right in the center-literally, the center of the Earth."

The findings are published in the journal Nature Geoscience.

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