Evolution of the Atmosphere
The Earth' surface was originally molten for many million years. It cooled down and formed a crust.
The volcanoes goave out lots of gas - including carbon dioxide, water vapour and nitrogen: atmosphere was formed.
The earl atmosphere was mainly CO2 and water vapour with virtually no oxygen. Oceans formed when water vapour condensed when Earth cooled.
Green plants evolved over most of the Earth - happy in CO2 atmosphere. Alot of CO2 dissloved in oceans. Green plants removed CO2 from the air and produced O2 by photosynthesis. When plants died and were buried, the carbon that was removed from the air became 'locked up' in sedimentary rocks as insoluble carbonates and fossil fuels.
Build up of oxygen killed off early organisms and allowed other more complex organisms to evolve - virtually no CO2 left.
Atmosphere - the mixture of gases surrounding the Earth. Mainly made up of:
Nitrogen - 78%
Oxygen - 21%
Argon - 1%. Also, the atmosphere contains small amounts of carbon dioxide and varying amounts of water vapour.
Human activity is adding small amounts of pollutants to the air. Some pollutants contain: carbon dioxide, carbon monoxide, particulates, sulfur dioxide and nitrogen oxides.
Pollutants come from different sources: from burning fuels - in power stations and vehicles. However, gases and particulates can also be released by nature e.g. volcanoes.
Some pollutants can be harmful to humans e.g. carbon monoxide reduces amount of oxygen that blood can carry. Or indirectly by damaging the environment: - sulfur dioxide can cause acid rain, pollutes rivers which could kill fish. Other pollutants e.g. CO2 can lead to climate change - rising sea levels and disruption to farming.