THE MYSTERIES OF EARTH'S CORE

Take even a quick peak beneath Earth's surface and you soon discover just how much we don't know about what's happening right under out feet

- COLIN STUART

WHAT'S IT REALLY MADE OF?

A set of strange signals are telling us a whole new story about what's happening at the core of our planet. And if we can decipher them, we might understand more about Mars's history

We spend so much of our time focused on the world around us that we rarely give much thought to what's going on beneath our feet. If Earth were an apple, the crust that we live on would only be as thick as the apple's skin.

Like an apple, Earth also has a core tucked away within, buried beneath a layer called the mantle.

The core formed early, just 200 million years after Earth itself coalesced, some 4.5 billion years ago.

Earth's core is large - almost equivalent to half the size of Mars and there's such extreme pressure crushing down on it that its temperature is as hot as the surface of the Sun.

Earthquakes have played an indispensable role in our understanding of this internal structure. The modern seismometer, invented in 1880, measures the vibrations from earthquakes as they ripple through the planet. In the early 20th Century, scientists assumed that Earth's core was completely molten and the material's movement was responsible for generating the planet's magnetic field. Then, in 1936, the Danish seismologist Inge Lehmann was able to determine, through the use of seismometers, that seismic waves were bouncing off something deep inside Earth. She correctly concluded that the planet's core was composed of two parts: a solid inner core, nested, Russian-doll-style, inside a molten outer core.

But more recent work is revealing that the reality could be a touch more complicated. Dr Thanh-Son Pham and Prof Hrvoje Tkalčić from The Australian National University tried something different.

DOWN TO THE CORE

1. Crust