Earth

Earth is the third planet from the sun and funnily enough, the one we know the most about.

The Earth's atmosphere is composed of; nitrogen 78%, oxygen 21%, argon 1% and traces of carbon dioxide, neon and helium. Water vapour concentrations are always variable, but are roughly 1%.

Earth has one natural satellite, the Moon, which orbits at 384,000km and is responsible for the tides.

From the surface, the atmosphere is labelled the troposphere for the first 14km up, then the tropopause (4km height), then the stratosphere (about 32km height), then the mesosphere (40km), then the ionosphere (over 600km in height) and finally the exosphere (another 200km), which is the boundary of space. The pressure at the top of the troposphere is only 10% of that at sea level and above this layer the pressure continues to drop. Weather as we know it also takes place in the troposphere, with the rising and falling of air through convection. The ozone layer is a thin region of the upper stratosphere which protects us from ultraviolet radiation. The ionosphere gets its name because it's teeming with ions and though it's very thin, it reflects radio waves, which is how radio communication works. It is also the region where the aurora take place.

Semimajor axis (km) 149.60x106 Perihelion (km) 147.09x106 Aphelion (km) 152.10x106 Mean orbital speed (km s-1) 29.78 Sidereal orbit period (days) 365.256 Tropical orbit period (days) 365.242 Length of day (hours) 24.0000 Sidereal rotation period (hours) 23.9345 Obliquity to orbit (deg) 23.45

Semimajor axis (AU) 1.00000011 Eccentricity 0.01671022 Inclination (deg) 0.00005 Longitude of ascending node (deg) -11.26064 Longitude of perihelion (deg) 102.94719 Mean longitude (deg) 100.46435 J2000 Data from NSSDC

The Earth's crust varies in thickness from 5-10km under the oceans and 20-70km on the continents and is mostly silicon dioxide (quartz). It is broken into several large pieces called plates, which effectively float on the liquid mantle. Where these plates are coming together, mountain ranges are formed, such as the Andes in South America. The mantle is roughly 2,900km thick, makes up 84% by volume and is solid/plastic. By composition, the outer mantle (350km thick) is mostly iron and magnesium silicates while the inner mantle is mostly magnesium, silicon, oxygen and iron. The mantle also contains some calcium and magnesium. The liquid outer core extends in radius from about 1220km to 3500km and is made of iron and nickel, whilst the solid inner core is volume contained by it and is almost entirely iron. It is thought the inner core may rotate slightly faster (0.5 degrees per year) than the the surface.

By mass, the Earth's composition is; iron 35.1%, oxygen 28.2%, silicon 17.2%, magnesium 15.9% and 1.5% of nickel, calcium and magnesium each. 

Mass (kg)	5.9736x1024
Equatorial radius (km)	6378.1
Polar radius (km)	6356.8
Mean density (kg m-3)	5515
Surface gravity (m s-2)	9.798
Escape Velocity (km s-1)	11.186
Black-body temp (K)	254.3
Solar intensity (W m2)	1367.6
Natural satellites	1

The Earth's maximum recorded temperature is 57.8 degrees on 13/09/1922 at El Azizia, Libya. The Earth's minimum recorded temperature is -89.4 degrees on 21/07/1983 at Vostok, Antarctica.