Inside the Earth: Layers of Our Planet

A planet with hidden layers

When you stand on the ground, the Earth feels solid and still. But our planet is not the same all the way through. If you could slice the Earth in half like an apple, you would see that it is built from layers, one inside the other.

There are four main layers: the crust, the mantle, the outer core and the inner core. Each layer is made of different things, and each one gets hotter the deeper you go. Let's travel from the surface all the way down to the centre.

The crust: the thin skin we live on

The crust is the outer layer, and it is where everything we know lives. Mountains, oceans, forests, cities and you are all on the crust.

Compared to the rest of the planet, the crust is surprisingly thin. Imagine an apple again: the crust is like the apple's skin. Under the oceans it can be only about 5 kilometres thick, and under the land it is usually 30 to 70 kilometres thick. That sounds like a lot, but the whole Earth is over 12,000 kilometres across, so the crust really is just a thin shell.

The crust is made of solid rock. The rocks you find on a walk, like granite, sandstone and limestone, all come from the crust.

The mantle: thick, hot, slow-moving rock

Below the crust is the mantle, the thickest layer of all. It reaches down about 2,900 kilometres and makes up most of the Earth.

The mantle is made of hot rock. Near the top it is solid, but deeper down it is so hot that the rock can slowly ooze and flow, a bit like very thick, sticky honey or modelling clay. It does not move fast — it might shift only a few centimetres a year, about as fast as your fingernails grow.

This slow movement is powerful. It pushes the giant pieces of crust, called tectonic plates, around the planet. When those plates bump, slide or pull apart, we get volcanoes and earthquakes. You can learn more about that in volcanoes and earthquakes.

The outer core: an ocean of liquid metal

Under the mantle is the outer core. This layer is not made of rock — it is made of metal, mostly iron and nickel. It is so hot here, around 4,000 to 5,000 degrees Celsius, that the metal has melted into a liquid.

So deep inside our planet there is a swirling, glowing ocean of liquid metal. As the Earth spins, this liquid metal moves and churns. This movement is amazing because it turns the Earth into a giant magnet. The invisible magnetic field it creates stretches out into space. It is the reason a compass needle always points north, and it also helps protect us from harmful rays coming from the Sun.

The inner core: solid metal at the centre

Right at the middle of the Earth is the inner core, a ball of metal about 1,200 kilometres across. This is the hottest place on Earth, around 5,000 to 6,000 degrees Celsius — almost as hot as the surface of the Sun.

Here is the surprising part. Even though it is the hottest layer, the inner core is solid, not liquid. How can that be? The answer is pressure. The weight of all the layers above presses down on the inner core so hard that the metal cannot melt or flow. It is squeezed into a solid ball.

Why the layers matter

The Earth's layers are not just an interesting picture. They shape our whole world:

• The crust gives us land to live on and soil to grow food.
• The mantle moves the plates that build mountains and open oceans.
• The core makes the magnetic field that guides compasses and shields the planet.

Without these layers working together, the Earth would be a very different, much less friendly place.

Try it yourself: build the Earth's layers

You can make a model of the Earth using things from the kitchen. With an adult's help, try this:

1. Roll a small ball of red modelling clay or play dough. This is the hot inner core.
2. Wrap it in a layer of orange clay. This is the outer core.
3. Add a thick layer of yellow or brown clay around that. This is the mantle — make it the biggest layer, because the mantle really is the thickest.
4. Finally, add a very thin layer of green and blue clay for the crust with land and sea.
5. Ask an adult to cut your model in half with a butter knife. Now you can see all four layers, just like a real cross-section of the Earth.

As you build, notice how thin the crust has to be compared to the giant mantle. That tiny outer layer is the part we call home.