Scientists have discovered a new layer of the Earth’s core.

A study conducted by seismologists from the Australian National University and published in the journal Nature on February 21 has suggested that the planet has a distinct fifth layer within its core.

The Earth’s structure has long been considered to have four distinct layers: the crust, mantle, liquid outer core, and solid metal core.

Scientists had predicted the existence of a fifth layer to the Earth’s core in 2002 based on similar seismic data used in this most recent study.

This is not the only recent discovery about the interior of our planet, as researchers observed evidence of what appears to be the slow reversal of the core’s rotation, as previously reported by The Dallas Express.

Researchers in the study documented earthquake waves traveling through the planet up to five times.

Thanh-Son Pham, the lead author of the study, said that this effect is a phenomenon that has never been recorded “in the history of seismology,” as past studies only documented a single reverberation, according to the Washington Post.

Researchers then observed that these waves, dependent on direction, passed through the innermost section of the Earth’s core at different speeds than the rest of the structure.

“Clearly, the innermost inner core has something different from the outer layer,” Pham, according to the Washington Post.  “We think that the way the atoms are [packed] in these two regions are slightly different,” he continued.

The researchers discovered what appears to be a 400-mile-thick metallic sphere within the Earth’s inner core. This sphere is theorized to be compromised of the same iron-nickel alloy that composes the rest of the core.

However, unlike the rest of the core, this layer is theorized to have a crystalline structure that caused the different speeds observed in the earthquake shockwaves.

Geophysicist John Tarduno told the Washington Post that this new discovery bolsters his own theories and findings about the planet’s core. Tarduno has theorized that slabs of oceanic crust sunk millions of years ago, compressing the mantle and changing the flow of heat.

Tarduno theorized that this event had impacted the development of the core.

“What we could be looking at in this innermost inner core is actually a signal of a change of the plate tectonics regime,” said Tarduno, according to the Washington Post.