By Jacqueline Howard / Source: HuffPost

An international team of researchers has discovered one of Earth’s deepest, darkest secrets: our planet’s inner core — once thought to be a ball of solid iron — has a hidden inner core of its own. And this so-called “inner-inner core” seems to have some very peculiar properties.

“The fact that we have two regions that are distinctly different may tell us something about how the inner core has been evolving,” Dr. Xiaodong Song, a professor of geology at the University of Illinois and co-author of a new paper about the discovery, said in a written statement. “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.”

For their study, the Illinois researchers and their counterparts at China’s Nanjing University measured how seismic waves resonated and traveled through the earth in the aftermath of earthquakes that occurred between 1992 and 2012. Analyzing an earthquake’s coda (the train of seismic waves that follow that quake) offers clues about what’s inside Earth.

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