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Diameter12756 km
Mass5.97 x 1024kg
Volume1.08 x 1021 m3
Average Density5.52 g/cm3
Average 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
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 MoonsOne
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 survive. 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 allow ultraviolet radiation from the Sun to pass through them. As the radiation strikes the ground it is absorbed and released again as infrared. CO2 and water do not let these wavelengths through, 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 now being destroyed by chemicals released by humans, 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 changing planet, with more than 500 active volcanoes during its lifetime. It has also been hit by meteorites from outer space, just like the other planets, but the effect of water and the movement of tectonic plates cause the craters to be eroded more quickly. Even so, around 100 impact craters have been identified worldwide. Tectonic plate movement is another process that changes our planet, it causes earthquakes and also allows continents to drift over millions of years. Earth’s geology is 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. This 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 directed 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