What Lies Beneath Our Feet?
We walk on the Earth every day, but the ground beneath us is only a very thin outer layer of a much larger world.
The Earth is roughly 6,371 kilometres in radius, yet humans have drilled only about 12 kilometres into it. Everything below that has been studied indirectly, using earthquakes, gravity, magnetic fields and other evidence.
The Earth has four broad layers:
Crust — the thin outer shell on which we live. Beneath the oceans it is thinner; beneath continents it is generally thicker.
Mantle — extending to about 2,900 km deep. It is made largely of hot, solid rock that can slowly flow over geological timescales. Movement in the mantle helps drive plate tectonics.
Outer Core — a vast layer of liquid iron and nickel. Its movement generates Earth's magnetic field—the invisible shield that helps protect us from charged particles from the Sun.
Inner Core — the deepest part, composed mainly of iron and nickel. Although extremely hot, it is solid because the pressure at the centre of Earth is enormous.
So beneath our feet is not an enormous empty cavern, as some old stories imagined, but a succession of rock, immense pressure, molten metal and a solid metallic centre.
And perhaps the most astonishing fact is this:
We have never seen the Earth's deep interior directly. Yet from earthquakes and other clues, science has been able to reconstruct what lies thousands of kilometres beneath us.
Every step we take is therefore on a remarkably thin outer skin of a living, moving planet.
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