Earth

The Earth is in third position relative to the Sun and, in many ways, absolutely unique in the Solar System. The distance to the host star is ideal, with temperatures on Earth being between the freezing and boiling points of water. The abundance of water on Earth and the thick atmosphere make life on our planet possible. To date, Earth is the only planet where we know that life exists.

The Earth roughly consists of three layers: an iron and nickel core, which is solid on the inside and liquid on the outside, a viscous mantle and a thin crust. Strong currents exist in the metallic core, and these are responsible for the Earth's magnetic field. The mantle material consists mainly of silicon, magnesium and oxygen, along with a layer of basaltic magma with a lot of calcium and aluminium. The outermost layer of the Earth floats on the mantle, being unconnected as a whole but divided into more than 20 continental plates. Matter from the mantle flows upwards into the mid-ocean ridges, thereby shifting the floating continental plates. As a consequence, America and Europe are today drifting apart several centimetres per year, while the plates over the Pacific are sliding over each other. The Alps were formed by a collision between the African and Eurasian plates over 45 million years ago. A zone of volcanic activity is created if an oceanic plate slides under a continental plate. These large-scale tectonic activities on Earth do not occur on any other planet in the Solar System.

The Earth's gaseous envelope, the atmosphere, is also made up of different layers. The troposphere, in which most weather phenomena take place, extends up to an altitude of ten kilometres. The stratosphere adjoins it. This contains the ozone layer, which absorbs a large proportion of the Sun's UV radiation that is essential for our survival. The gas in the outer areas of the atmosphere is predominantly ionised by the hard radiation of the Sun (individual particles are therefore electrically charged), and this is also referred to as the ionosphere, in which fabulous aurorae (e.g. the northern lights) can occur. The air density in the layers below an altitude of 150 kilometres is high enough to cause most meteoroids to burn up if they are on a collision course with Earth.