For 200 million years, the proportions of different gases in the atmosphere have been pretty much the same as they are today
Composition of the atmosphere
Nitrogen (78%)
Oxygen (21%)
Other gases (1%, including carbon dioxide (0.04%), water vapour and noble gases)
Carbon dioxide
Produced by burning fossil fuels in power stations, vehicles and homes
Methane
Produced by cattle and landfill sites
Greenhouse gases
Allow shorter wavelength rays (e.g. ultraviolet) to pass through, but absorb longer wavelength rays (e.g. infrared) emitted by the Earth's surface, causing temperature rise
Carbon monoxide
A toxic, colourless and odourless gas
Sulphur dioxide and oxides of nitrogen
Cause respiratory problems in humans and acid rain
Particulates
Cause dimming and health problems for humans
Complete combustion
Occurs when there is enough oxygen available for all the carbon atoms in the fuel to burn and form carbon dioxide and water
Incomplete combustion
Occurs when there is a shortage of oxygen, producing carbon monoxide and water (also produces carbon particulates)
