The Earth's surface

The ground underneath us seems solid and stable, right? You can feel it under your feet, walk, jump and nothing happens to it. But is the surface of the Earth really as stable as it seems? If we could cut the Earth open, we would see it has layers that resemble an egg. In the centre, like an egg’s yolk, there is a liquid core.

And just like the egg yolk is surrounded by egg white, the Earth’s core is surrounded by a layer of molten rock - mantle. The outermost layer of the Earth - the Earth’s crust - resembles an egg’s shell. It’s hard and brittle, and very thin compared to the other layers. The crust covers the whole surface of the planet. Together with the uppermost part of the mantle, the crust forms the lithosphere.

In most places, the Earth’s crust is covered with a layer of soil. This is where the Earth’s lithosphere meets water, air, and life. Soil consists of small particles of rock, salts, and remains of organic matter. It also contains oxygen, nutrients, and water, which create a perfect environment for organisms to live in. About seventy percent of the Earth’s surface is covered by ocean water.

The crust underneath the oceans - the oceanic crust - consists of magma that has cooled down fairly quickly and formed dense rock, such as basalt. The crust under the ocean is only about five to ten kilometers thick. The crust beneath the land - the continental crust - is thicker and less dense than the oceanic crust. This is about twenty five to seventy kilometers thick and consists of many different kinds of rocks, mostly granite. The rocks in the Earth’s crust are made up of different elements - mostly oxygen and silicon, with smaller amounts of aluminium, iron, calcium, sodium, and magnesium, and tiny percentages of other elements.

Most of these elements are combined with each other and form compounds. We call these compounds minerals. So the Earth’s crust consists of a variety of different elements, minerals, and types of rock. It is also made up of several different pieces, constantly moving relative to each other! The Earth’s crust consists of seven major and a few smaller pieces floating on top of the Earth’s mantle.

These pieces of the Earth’s lithosphere are called tectonic plates. The movement of tectonic plates is very slow, but it can cause earthquakes and create new landforms, like mountain ranges or rift valleys. But the movement of tectonic plates is not the only factor that affects the Earth’s surface. External factors such as wind, rain, and changing temperatures play a role too, since they wear down - erode - the terrain. In this way, different types of landscapes are formed, such as plains, valleys, and cliffs.

Humans also have a great impact on the shape of the Earth’s surface by, for example, mining for minerals or building roads and tunnels. So the Earth’s surface might seem completely fixed and permanent, but in fact, it is changing and transforming all the time.