The Earth is unlike every other planet in the Solar System in a number of different ways.

• It is the only planet that has an atmosphere containing 21 percent oxygen.
   
• It is the only planet that has liquid water on its surface.
   
• It is the only planet in the solar system that has life.
   
• The Earth is the only inner planet (Mercury, Venus, Earth and Mars) to have one large satellite, the Moon.  Mars has two very tiny moons.  Mercury and Venus have none.
   
• The Earth is fragile.  Its surface is split into plates (tectonic plates) which float on a rocky mantle – the layer between the surface of the earth, its crust, and its hot liquid core.  The inside of the Earth is active andearthquakes, volcanoes and mountain building takes place along the boundaries of the tectonic plates. 
• When viewed from outer space much of the Earth’s surface cannot be seen because of clouds of water vapour.  The water vapour makes the Earth, when seen from outside, into a brilliant shining orb, as you can see in Figure 1.
• The Earth is the third planet from the Sun and comes between the planet Venus and the planet Mars.
 
Figure 2. The planets of the Solar System.
• The Earth takes 365¼ days to complete its orbit round the Sun.  The Earth’s year is therefore 365 days long but the ¼ days are added up and every fourth year has one extra day, on the 29th of February.  This fourth year is called a Leap Year (366 days) and is always a year which can be divided exactly by 4 – 2000, 2004, 2008, 2012, 2016.
• The planets closer to the Sun, Mercury and Venus, have shorter years than the Earth.  The planets further away from the Sun have longer years; Pluto takes 249 of our years to make one orbit of the Sun.
   
• As the Earth orbits round the Sun it turns on its axis, rotating right round in 24 hours.  The side of the Earth that faces the Sun has daytime and the side of the Earth that is turned away from the Sun has night-time.  When it is daytime in Britain, it is night-time on the opposite side of the Earth in New Zealand.
   
• As the Earth orbits round the Sun it tilts very slightly and so gives us the seasons.  When the Earth has tilted so that the northern half of the Earth is a little away from the Sun, the northern hemisphere (meaning half of the Earth’s sphere) has winter.