Shocking discovery made 2,700km below Earth's surface

Scientists have made a shocking discovery 2,700 km below the surface of our planet. A team from ETH Zurich has discovered solid rock flowing deep underground. The strange rocky flow is neither liquid like molten magma nor solid like the brittle rocks we see on the surface.

This is the first confirmation of scientists' assumptions that rocks in the bowels of the planet move under the influence of convection currents, like water in a boiling cauldron, writes the Daily Mail.

"Our discovery shows that the Earth is not only active on the surface, but also in motion deep inside," said lead author Professor Motohiko Murakami. Confirming this theory now allows scientists to begin mapping hidden currents in the rock deep inside the planet. This could one day explain the invisible engine that drives volcanoes, earthquakes, tectonic plates and even the Earth's magnetic field.

Professor Murakami adds: "We have finally found the last piece of the puzzle."

Scientists divide the Earth into three main layers: the crust, the mantle and the core, writes the Daily Mail. The astonishing discovery was made by studying a strange region of the mantle known as the D layer. When seismic waves from earthquakes reach this layer, they suddenly speed up, as if they were penetrating a different type of material.

Professor Murakami had previously discovered that perovskite, the material that makes up much of the lower mantle, transforms into a new mineral around the D layer. Under extreme pressure and high temperature, perovskite transforms into post-perovskite, which Professor Murakami believes could explain the sudden change in the behaviour of seismic waves.

But it soon became apparent that this alone was not enough to explain why the earthquake waves sped up so much 1,700 miles below the surface, the Daily Mail continues. The researcher's breakthrough was the discovery that the hardness of post-perovskite depends on how its crystals are arranged.

Professor Murakami tells MailOnline: "Post-perovskite has an unusual property - it is extremely hard in only one particular crystallographic direction."

Since seismic waves travel faster through harder materials, this explains why earthquake waves suddenly become so fast in only one particular region.

In a highly unusual experiment, Professor Murakami decided to recreate the conditions found nearly 2,000 miles below the Earth's surface to see how it could happen.

Professor Murakami told MailOnline: "By placing a very small sample between two single crystal diamonds with pointed ends, we can create extremely high pressures. And through transparent diamond windows we can directly observe the sample under high pressure."

Tiny grains of perovskite were crushed under pressures of up to 115 gigapascals, more than 16 million pounds per square inch, to recreate the conditions of the D layer. Under intense heat and pressure, the crystals in the post-perovskite aligned themselves in a line, all oriented in one direction. Testing showed that only this particular alignment was rigid enough to produce the seismic acceleration the scientists were looking for. That meant something must be happening around the D layer to cause all the mineral crystals to point in the same direction.

According to the researchers, this could only have been caused by solid rock flowing horizontally along the boundary between the Earth's mantle and core.

So when the rock is constantly moving in one direction, all the crystals are forced to point in one direction, and the post-perovskite becomes much harder. This means that the D layer is actually a vast underground layer of super-hard rock, 1,700 miles below the surface, the Daily Mail reports.

Professor Murakami says: "The mantle is dense, but it moves at a very slow rate - just a few centimetres a year. This movement is called mantle convection. Even though the mantle is solid, it can flow like a liquid for long periods of time if it has the right viscosity. On a time scale of 4.6 billion years, even a few centimetres a year results in a huge movement."