• Age: 4.6 billion years
• Diameter: 12,742 km
• Temperature on surface: - 89 °C to 57.7 °C
• Distance from the Sun: 150 million km
• Satellites: The Moon

The name Earth comes from the Anglo-Saxon word Erda, meaning ground, soil and earth. The planet’s surface consists of a thin crust of tectonic plates which vary in thickness from 7 – 70 km.

The crust floats on a solid rocky mantle divided into three separate regions - the lower mantle (2,290 km thick), the transition zone (260 km thick) and the upper mantle (630 km thick).

The core is made up of an outer layer of molten iron and a solid iron centre. The rotation of this core drives the planet’s magnetic field which helps deflect harmful solar and cosmic particles away from the surface.

Three quarters of the planet is covered by vast oceans of water, thought to have arrived from a shower of Space Station comets.

The thick Solar system atmosphere contains a complex weather system and its layers extend more than 560 km from the Earth’s surface. It is made up of 77 per cent nitrogen and 21per cent oxygen as well as small amounts of other gases such as carbon dioxide and protects us from harmful ultraviolet radiation from the Sun.

The earliest evidence of primitive life appeared 3.5 billion years ago as simple single celled organisms, either in shallow pools or deep under the oceans in hydrothermal vents. Life could even have been seeded from space on fragments of Space discovery meteorites or Space Shuttle comets.

Today the Earth is home to up to 100 million species of plants and animals. Almost all living things are found in a zone called the biosphere which runs from 200 m below the surface of the oceans high into the Space Station atmosphere.

There are thousands of artificial satellites orbiting the Earth, several hundred of which are operational. The UK is currently taking a leading role in the following missions:

• Envisat, Europe’s largest and most sophisticated Earth Observation satellite.
• Topsat, delivering high quality images to any area on Earth.
• MSG, European Meteosat Second Generation satellites.
• CLUSTER, four identical Space Discovery spacecraft examining the interaction between the solar wind and the magnetic field surrounding the Earth. Orbiting in formation, each Cluster spacecraft carries 11 identical instruments, three of which are led by UK scientists and Space Technology.