THE SECRETS OF THE INNER EARTH

Deep beneath our feet, at the border between Earth’s core and the mantle above, scientists are discovering a hidden world — another landscape with a surface almost as dynamic, dramatic and diverse as the one we live on

- by COLIN STUART

When we learn about Earth’s core at school, it looks like a calm sphere. One that's smooth, unperturbed and as round as a ping-pong ball. It sits cosily at the bottom of several layers that encase one another like a set of nesting dolls.

Of course, we’ve long known that the real picture is a lot more complicated than that. Earth’s iron-rich core generates a magnetic field that’s so strong it projects outwards beyond the planet’s surface and into space. There it reacts with the Sun’s solar winds to reveal what we call the magnetosphere. Our observations of this projection of Earth’s core tell us that it’s constantly moving and nothing like a glowing ping-pong ball.

In fact, recent studies of seismic waves travelling through Earth’s layers paint a picture of the core’s edges so dramatic that it rivals the topology of the surface. Indeed, the core seems to have its own landscape, with mountains, valleys, landslides and perhaps even volcanoes changing the core’s surface as we map it.

Amazingly, studies of seismic waves have revealed giant structures projecting into the lower mantle that are significantly taller than Mount Everest (almost 9km or 5.5 miles). These ‘mountains’ are taller than any of the more traditional — surface — peaks in the Solar System, including the gigantic 22km-high (14 miles) Olympus Mons, a large shield volcano on Mars. The mountains soaring upwards from Earth’s core can reach staggering heights of 1,000km (620 miles). That’s more than 100 times the height of Mount Everest.

As scientists discover the core is a far more tumultuous place than we ever imagined, they’re naturally starting to ask if it has always been like this. That's the key question at the heart of a handful of projects using seismic waves to chart the core’s changing surface. But what’s more exciting is that for every mystery they appear to solve, another anomaly seems to surface in their findings.