James Stewart

In order to get to our planet's core, we need to go down.

Call it my version of a journey to the centre of the Earth.

Each layer has its own role in creating, sustaining and sometimes destroying the world above.

And all of them are influenced by the solid iron heart.

Here at the surface, we walk upon the crust, a mere brittle shell.

Though it feels pretty solid to us, it is in fact fractured into giant tectonic plates that drift, collide and grind past each other, causing violent earthquakes and devastating volcanic eruptions.

How it moves is all thanks to the layer below, the mantle.

This layer also appears solid, but is actually flowing very, very slowly, at the rate of a few centimetres a year.

This tiny but inexorable movement contributes to the plate tectonics that impact our surface world.

Dig deeper still and you reach the outer core, a sea of iron and nickel with its own heat-driven currents.

Its motion generates the Earth's magnetic field, which protects life on our planet from deadly solar particles.

Finally, suspended in this outer core is that primarily iron inner core.

Here, the temperature reaches 6,000 degrees Celsius.

Due to the immense pressures, the metal isn't liquid, but solid, forming a spheroid shape, like a slightly squashed sphere.

This is our planet's boiler room.

Its heat triggers the processes in the layers above.

driving those all-important convection currents in the outer core and ultimately contributing to the plate tectonics that shift the Earth's crust.

It's easy to take for granted that we understand our planet's structure, but in reality that knowledge was incredibly hard won.

It's one thing studying, cataloguing and theorising about the world we can see all around us, but quite another to investigate our planet's hidden interior.

So how do we know what's down there?