The Earth's Atmosphere


History of our Atmosphere

- the Earth's early atmosphere was formed by volcanic activity

- it probably consisted mainly of carbon dioxide, there may also have been nitrogen and water vapour, together with traces of methane and ammonia

- as plants spread over the Earth, the levels of oxygen in the atmosphere increased

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Our Evolving Atmosphere

- photosynthesis by algae and plants decreased the percentage of carbon dioxide in the early atmosphere. The formation of sedimentary rocks and fossil fuels that contain carbon also removed carbon dioxide from the atmosphere

- any ammonia and methane was removed by reactions with oxygen, once oxygen had been formed by photosynthesis

- approximately four-fifths (about 80%) of the atmosphere today is nitrogen, and about one-fifth (about 20%) is oxygen

- there are also small proportions of various other gases, including carbon dioxide, water vapour and noble gases

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Greenhouse Gases

- the amount of carbon dioxide in the Earth's atmosphere has risen in the recent past, largely due to the amount of fossil fuels now burnt

- it is difficult to predict with complete certainty the effects on climate of rising levels of greenhouse gases on a global scale

- however, the vast majority of peer reviewed evidence agrees that increased proportions of greenhouse gases from human activities will increase average global temperatures

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Global Climate Change

- reducing greenhouse gases in the atmosphere relies on reducing the use of fossil fuels, mainly by using alternative sources of energy and conserving energy

- the economies of developed countries are based on energy obtained from fossil fuels, so changes will cost money to implement

- however, changes are needed because of the potential risks arising from global climate changes, such as rising sea levels, threats to ecosystems and different patterns of food production around the world

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Atmospheric Pollutants

- when hydrocarbon fuels are burnt in plenty of air, the carbon and hydrogen in the fuel are completely oxidised. They produce carbon dioxide (the main greenhouse gas) and water.

- sulfur impurities in fuels burn to form sulfur dioxide, which can cause acid rain. Sulfur can be removed from fuels before they are burned, or sulfur dioxide can be removed from flue gas.

- changing the conditions in which hydrocarbon fuels are burnt can change the products made.

- in insufficient oxygen, poisonous carbon monoxide gas is formed. Particulates of carbon (soot) and unburnt hydrocarbons can also be produced, especially if the fuel is diesel. They can cause global dimming.

- at the high temperatures in engines, nitrogen from the air reacts with oxygen to form oxides of nitroge. These cause breathing problems and can also cause acid rain.

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