WHAT truly lies beneath Earth's surface largely remains a mystery but scientists have just discovered a new hidden "zone."
The previously unknown layer has remained a secret until now and is said to be 100 miles below the Earth's crust.
The hidden layer is made up of partly molten rock.
It was revealed in a groundbreaking study that could help us unlock some of Earth's secrets, including how it formed.
Scientists think it could also change what we know about tectonic plates and how they move.
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A team of scientists was led by Junlin Hua, a postdoctoral fellow in geosciences at the University of Texas.
They discovered the new zone and have just published a study about it in the journal Nature Geoscience.
Hua told Vice's Motherboard: "We were amazed by how well the observation…matches our intuition.
"I was also a little surprised by how widespread it is."
The study describes the new zone as "a globally extensive, partially molten zone embedded within the asthenosphere".
The asthenosphere is a weak layer beneath the Earth's crust.
It's said to start about 62 miles below the surface and ends about 255 miles down.
The new zone is within this, and scientists hope it will provide answers as to how the flow of the asthenosphere affects the tectonic plates above it.
Hua was mapping the asthenosphere when he stumbled across the hidden area.
The researcher reportedly told Vice: "I was studying Turkey at that time, and found a seismic signal that marks the lower reach of a seismic low-velocity layer there.
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"People have been talking about the upper boundary of the low-velocity layer a lot, but the lower reach is less mentioned, and I was surprised by that clear lower reach in Turkey.
"So I decided to study it across the globe to see how prevalent such lower reach is, and we found in this study that it is actually pretty widespread, and the lower reach just corresponds to the bottom of the layer with partially molten rocks."
Further research will be conducted on the zone to hopefully unlock its secrets.