Scientists have uncovered six never-before-seen mystery structures lurking deep inside the Earth.

Although our planet’s deep layers are totally inaccessible, scientists can use the seismic waves from powerful earthquakes to probe the hidden depths.

Now, Chinese scientists have uncovered structures sitting on the boundary between the viscous mantle and the liquid outer core, 1,800 miles (2,900km) beneath our feet.

They could include pieces of the continental crust or even the remains of Theia, a Mars-sized protoplanet believed to have formed the moon after hitting Earth 4.5 billion years ago.

Under the vast pressures and incredible temperatures at the mantle boundary, these chunks transform, partially melt, or undergo mineral transformation.

Read more: What lies beneath: Scientists discover six never-before-seen mystery structures lurking deep inside the Earth