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Diameter12756 km
Mass5.97 x 1024 kg
Volume1.08 x 1021 m3
Mean Density5.52 g/cm3
Mean Distance from Sun150 x 106km = 1 AU
Eccentricity of Orbit0.017
Inclination of Equator to Orbit23.5°
Inclination of Orbit to Ecliptic
ColourBlue and Green
TemperatureAverage: 14°C
ranges from -50°C to +40°C
AtmosphereNitrogen (78%)
Oxygen (21%)
Argon (0.9%)
Small amounts of carbon dioxide, hydrogen and others
Some water vapour
Length of Day23.9 hours
Length of Year365.25 days
No. of Moons1
Surface Pressure1 atmosphere (1 bar)
Gravity9.81 N/m/s2
Escape Velocity11 km/s

Earth is the third planet in our Solar System and is the only planet in the Universe known to support life. 71% of its surface is covered by water.

The greenhouse effect raises the average temperature of the Earth from –21 C to +14 C. Without the greenhouse effect, our oceans would be frozen and life could not exist. The greenhouse effect is now threatening our planet because it is out of control due to the high levels of carbon dioxide and water vapour in our atmosphere. These are transparent to incoming ultraviolet radiation from the Sun. As the radiation strikes the surface it is absorbed and re-radiated in the infrared. CO2 and water are both opaque at these wavelengths, and so the radiation cannot escape. The atmosphere therefore warms up.

The Earth is protected from harmful solar radiation by the ozone layer. This radiation would otherwise kill all life on the planet. Our ozone layer is currently being destroyed by chemicals released by human activity, creating holes over the North and South poles.

Scientific data showing the extent of the ozone hole over the South Pole

Earth has only one moon, but it also has another ‘companion’, Asteroid 3753(1980 TO) that regularly passes close to the planet.

Earth is a geologically dynamic planet, with more than 500 active volcanoes during its lifetime. It has also been bombarded by meteorites from outer space, just like the other planets, but water erosion and tectonic plate movement cause the craters to be obliterated relatively quickly. Nevertheless, around 100 impact craters have been identified worldwide. Tectonic movement is another ongoing process that shapes our planet, causing not only earthquakes but also continental drift over millions of years. Earth’s geology is therefore dominated by water erosion and plate tectonics. The aurora, as seen from the Space Shuttle

The Earth has the strongest magnetic field of all of the terrestrial planets, which means that it must have a molten core. In fact the outer core is liquid but the inner core is solid. The magnetic field protects us from the solar wind that would otherwise bombard us with highly charged electrons and protons. Instead they are funnelled by the magnetic field down to the poles where they interact to produce the aurora.

Planets Introduction



The Moon










Extra-Solar Planets

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Authors: Carolyn Brinkworth and Claire Thomas

Last updated: July 2001