Earth

Earth is the largest of the four inner planets. Third in order of from the Sun, 71% of its surface is taken up by oceans. Water is also present as droplets or ice particles that make up the clouds, as vapour in the atmosphere and as ice in polar areas or on high mountains.

Liquid water is essential for the existence of life on Earth, the only body in the Solar System where life is known to be present. Earth's distance from the Sun-neither too close nor too far-produces exactly the right temperature range. The atmosphere traps enough of the Sun's energy to avoid temperature extremes. It also screens the harmful rays of the Sun and acts as a shield against bombardment by meteoroids.

Earth's magnetic field is generated by electrical currents produced by the swirling motion of the liquid inner core. The magnetic field protects Earth from the solar wind Earth's outer shell, made up of the rocky crust and partly-molten upper mantle, is divided into about 15 separate pieces, called tectonic plates. Volcanoes and earthquakes occur where plate edges meet.

Fact file
Diameter: 12,756 km Day: 23 hours 56 minutes

Year 365.26 days

Average distance from the Sun: 149.7 million km

Surface temperature: -70 to +55°C

Atmosphere: nitrogen, oxygen, water vapour

Number of moons: 1