Evolution of the Earth's Atmosphere

When the Earth first formed 4.54 billion years ago, its surface was molten. As it cooled, volcanoes were formed. These volcanoes released various gases. Around 4600 million years ago the Earth’s atmosphere was made up of Carbon Dioxide, Water Vapour, Nitrogen, Ammonia, Hydrogen Chloride, Sulphur Dioxide, Hydrogen and the Noble gasses. There was no oxygen at this time. Oxygen only appeared in the atmosphere around 3500 million years ago when the first simple organisms began releasing it.

Most of the Earth’s atmosphere (78.08%) now is made up of Nitrogen. Another 20.95% is mage up of Oxygen. A number of other gases, including Argon and Carbon Dioxide, are present in trace amounts. The Carbon Dioxide levels in the atmosphere have lowered so much from what they were millions of years ago because over time the gas was dissolved in oceans and trapped underground and in sedimentary rocks.

As previously mentioned, water vapour was one of the gases that made up the atmosphere around 4600 million years ago. There was no water in liquid form then because temperatures were too hot. As the Earth began to cool, so did the water vapour. It cooled enough to condense and form oceans. The oceans were started as pools of water in low-lying areas. Minerals dissolved into these pools from both the air and the rocks that the water ran off. These new water pools became ideal for the basic organisms to form and live. The first living organisms on Earth used photosynthesis to make their energy. Photosynthesis is one of the main processes that removes Carbon Dioxide from the atmosphere. The equation for photosynthesis is:
Carbon Dioxide + Water = Glucose + Oxygen
6CO2 + 6H20 = C6H12O6 + 6O2

It was this that led to less Carbon Dioxide and more Oxygen in our atmosphere today.

The graph above shows Carbon Dioxide levels and temperature changes since 1880. We can see that over the entire time period, both the Carbon Dioxide concentration and the temperature are rising. From around 1960 onwards the rising of the two factors looks to be at a similar rate. This suggests that the rise in levels of Carbon Dioxide links to the temperature increase.
Carbon is removed from the atmosphere when:

It is absorbed into the ocean.

It is used by green plants in photosynthesis.

Carbon is also released into the atmosphere by certain processes including respiration and combustion.
Respiration is the opposite of photosynthesis. All living things respire. Green plants release oxygen as a product of photosynthesis. The equation for respiration is:
This means that whilst plants are using the carbon dioxide from the atmosphere, other living things are still producing it.

Combustion is the other important process that releases carbon dioxide into the atmosphere. When fossil fuels are burnt they release various gases, including carbon dioxide. This is because fossil fuels are made of plants that have decayed and been stored underground. The deposits of dead plants (in the form of things such as coal) contain carbon dioxide because that is what would have been in the plants when they died. Burning these releases the carbon dioxide so it ends up back in the atmosphere.