1800 miles underground lies a mysterious zone between the Earth's mantle and core. Nobody is quite sure what's down there, but new evidence suggests the area reaches temperatures of 7000 degrees Fahrenheit, meaning it could be a vast magma ocean.
Geophysicists have a pretty good handle on the Earth's overall internal composition. At the center, there's a core made of liquid iron, and above that is a solid mantle composed of iron, silicon, and magnesium oxides. But we're still struggling to work out exactly what lies at the boundary between these two areas. We know the pressure there is about 1.4 million times that of the surface atmosphere, and it must reach temperatures around 7000 degrees Fahrenheit, or about 4200 Kelvin. But what that means for the chemical reactions and changes in matter that happen down there is a mystery.
However, a phenomenon known as seismic waves provides some insight. These are huge waves of energy that pass through the Earth's interior, and they can help us work out the density and composition of the area they're traveling through. Scientists have detected a massive reduction in the speed of these waves right around the border between the mantle and the core. That has led scientists to hypothesize there's a huge magma ocean created by the partial melting of the mantle.
Now, fifteen years after this idea was first put forward, we have proof. Using diamond anvil cells, geophysicists can recreate the unimaginable pressure of the mantle-core border, and a special heating layer can recreate the extreme temperatures. French researchers subjected tiny representative samples of the mantle to these conditions.
They found the mantle actually undergoes partial fusion under these conditions, and this process creates dense liquids that can hold a number of chemical elements. That's strong evidence in favor of a magma ocean, and that last bit about chemical elements is particularly exciting. Knowing what elements are in the magma ocean could help us better understand the underlying mechanisms of how Earths' different layers separated out, which was a crucial part of its formation 4.5 billion years ago.