In research that didn't involve incredible advances in drilling technology, researchers have found some surprising secrets at our planet's core. What was once thought to be a single core of solid iron actually contains an inner core of its own with properties very different from what geologists who measured earthquake waves now refer to as the "outer inner core," CNET reports.

The iron crystals in the "inner inner core" are aligned on an east-to-west axis, while the outer ones are aligned north to south, according to the researchers, whose study was published in the journal Nature this week.

The newly discovered core is about half the diameter of the original core area, which is around the same size as the moon. Researchers say that analysis of the core, which began to solidify around a billion years ago, could hold the key to how our planet evolved.

The team discovered the inner core by analyzing the seismic waves that echo after earthquakes. "The earthquake is like a hammer striking a bell; much like a listener hears the clear tone that resonates after the bell strike, seismic sensors collect a coherent signal in the earthquake's coda," a University of Illinois report on the findings explains.

It's not clear why the inner core is so different from the outer one, but a University of Cambridge expert tells the BBC that it seems "something very substantial happened to flip the orientation of the core" around half a billion years ago.

(An earlier study found that the core is as hot as the surface of the sun.)

This article originally appeared on Newser: Earth's Core Has Its Own Core

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