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C13: THE EARTH'S ATMOSPHERE (Our Evolving Atmosphere (Photosynthesis…
C13: THE EARTH'S ATMOSPHERE
The History of Our Atmosphere
The Earth's early atmosphere was formed by volcanic activity
It probably consisted of mainly 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
Our Evolving Atmosphere
Photosynthesis of plants decreased the percentage of carbon dioxide in the early atmosphere
The formation of sedimentary rocks and fossil fuels also removed carbon dioxide from the atmosphere
Any ammonia and methan was removed by reactions with oxygen, once oxygen had been formed by photosynthesis
About 80% of the atmosphere today is nitrogen and about 20% is oxygen
There are also small amounts of various other gases, including carbon dioxide, water vapour and noble gases
Greenhouse Gases
The 3 main greenhouse gases are carbon dioxide, water vapour and methane
What is Their Effect?
The Sun's rays enter the Earth's atmosphere, heat is emitted back from the Earth's surface, some heat passes back our into spaces, but some heat is absorbed by carbon dioxide, a greenhouse gas, and becomes trapped within the Earth’s atmosphere. The Earth becomes hotter as a result
The amount of carbon dioxide in the Earth's atmosphere has risen in the recent past, largely due to the amount of burnt fossil fuels (coal, natural gas, crude oil)
Although it is hard to predict the long term global effects of greenhouse gases, many agree that increased amounts of greenhouse gases from human activities will increase the average global temperature
Atmospheric Pollutants
When hydrocarbons are burnt in plenty of air, the carbon and hydrogen in the fuel are completely oxidised, producing carbon dioxide 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 hydrocarbons fuels are burnt can change the product made
In insufficient oxygen, carbon monoxide gas is formed. Particulates of carbon (soot) and unburnt hydrocarbons can also be produced, especially if the fuel is diesel, which can cause global dimming
At high temperatures in engines, nitrogen from the air reacts with oxygen to form oxides of nitrogen, which can cause breathing problems and acid rain
Global Climate Change
Reducing greenhouse gases in the atmosphere relies on reducing the use of fossil fuels, mainly by using alternative energy sources 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, ecosystem threats, and different patterns of food production around the world