The Earth's crust is the outermost layer of the Earth, and is made up of rocks in a solid form. Beneath the crust, we find the mantle and the core.
There are two different types of crust. The continental crust is usually between 30 and 50 kilometers thick. It has a relatively low density and is found on the continents and under the continental shelf. Here we find the oldest rocks on Earth, with ages up to 4400 million years.
The oceanic crust is formed along mid-ocean ridges in the deep sea and consists of "young" rocks, none older than 175 million years. It has an average thickness of 5-7 km and consists of dark rocks with a higher density than the continental crust. It has the highest density and is thinnest along the mid-ocean ridges.
Why do the plates move?
The lithosphere is the outer, solid part of the earth, comprising both continental crust and oceanic crust, along with the upper part of the underlying mantle. It is divided into several tectonic plates that can move over the softer, plastic asthenosphere in the upper part of the mantle.
Plate movements occur due to slow flows in the mantle and are driven by heat rising from the earth's interior. Movements along plate boundaries can also trigger volcanic eruptions and earthquakes.
What happens during plate collisions?
Where a plate with oceanic crust collides with a plate with continental crust, the heavier oceanic crust will sink obliquely down into the mantle beneath the continental crust. This is called subduction.
As the plate sinks into the mantle, pressure and temperature increase, and the rocks may gradually melt and form magma that rises to the surface. Therefore, strong volcanic activity is common along such subduction zones.
Where two continental plates collide, high mountains rise with a compressed crust that can become more than 70 km thick. An example of such a mountain range is the Himalayas, where India collides with Asia.
What is the mantle?
The mantle lies between the earth's crust and core and is the part of the globe with the largest volume. The upper part consists of heavy rocks in solid form, while the rock becomes softer deeper down as the temperature increases.
The temperature in the mantle increases from 1250 °C to 3370 °C down to a depth of 2,890 kilometers. In the mantle, we also find zones with partially melted rock.
What is the core?
The core is the inner part of the earth and is divided into an outer core and inner core. The temperature in the core increases with depth from 3370 °C to more than 5000 °C. Due to the high temperature, the outer core consists of liquid iron and nickel. It is about 2,300 km thick. Flows in the outer core are the reason for the formation of a magnetic field on earth.
The inner core, from a depth of about 5,000 kilometers down to the earth's center at almost 6,400 kilometers, is mainly composed of iron and nickel. The very high pressure makes the inner core solid despite the high temperature.