What is the structure of the Earth?

What is the structure of the Earth?

The Earth is composed of several layers, each with distinct properties. You can imagine the planet like a layered ball: a thin outer crust, a thick rocky mantle, and a hot metal core at the centre.

The Crust

The crust is the outer skin of the planet. It is the layer we live on and is only a tiny fraction of the Earth’s total thickness.

There are two types of crust:

• Continental crust – forms the land. It is quite thick (around 30–50 km deep), less dense and mainly made of granite-type rocks.
• Oceanic crust – lies beneath the oceans. It is thinner (around 6–8 km), denser, and mostly made of basalt.

Both types of crust are broken into massive slabs called tectonic plates. These plates “float” on a deeper, semi-solid part of the Earth, and their movement causes earthquakes, volcanic eruptions and mountain building.

The Mantle

Beneath the crust is the mantle, the largest layer of the Earth. It extends down for nearly 3,000 km.

• The upper mantle is mostly solid rock.
• Deeper down, high temperatures melt some minerals, creating a partly molten layer called the asthenosphere.

The asthenosphere is important because it acts like a “soft” layer. Tectonic plates move over it very slowly, pushed and pulled by heat and pressure inside the Earth.

The Core

At the centre is the core, made of iron and nickel.

It has two parts:

• Outer core – a liquid layer that surrounds the very centre of the Earth. The movement of this liquid metal creates the Earth’s magnetic field.
• Inner core – a solid ball of metal. Even though it is extremely hot (over 5,000°C), the huge pressure keeps it solid.

How do we know what’s inside the Earth?

Humans have only drilled a short way into the crust, so scientists rely on indirect evidence:

• Seismic waves from earthquakes change speed and direction when they pass through different materials. This helps scientists map each layer.
• Meteorites are made of the same materials thought to exist inside Earth’s core.
• Satellites and computer models help estimate temperatures, density and movement inside the planet.