Evolution of the Atmosphere

• the atmosphere is 80% nitrogen
• the atmosphere is 20% oxyegn
• all other gases in the atmosphere make up <1%
• This only a theory supported by lots of evidence, it is not exactly proven
• In the first billion years of eath's history, there was intense volcanic activity. There were loads of carbon dioxide, water vapour and nitrogen. There were smaller amounts of methane and ammonia. It was much like the atmospheres of mars and venus today.
• In the first billion years of earth the water vapour in the atmosphere condensed to create our oceans. This allowed lots of the carbon dioxide in the atmosphere to dissolve in the ocean. The carbon formed precipitates and finally sediments in the sea bed.
• 2.7 billion years ago algae began to appear, slowly at first but more rapid as green plants evolved. This is as both of these organisms can photosynthesise. As the alage and plants photosynthesised over the years the volume of carbon dioxide decreased and the volume of oxygen increased.
• Oxygen allowed complex life like animals to evolve
• Algae and plants could only hold small amounts of carbon in their bodies
• When algae and green plants died they fell to sea bed and were buried in layers of sediment. Over millions of years this sediment formed oil, gas and sedimentary rock. This trapped the carbon from coming back into the atmosphere.
• Crude oil and natural gas are mainly formed from dead plankton
• coal is a sedimentary rock mostly formed from dead plant material
• lime stone is a sedimentary rock that is formed from the calcium carbonate of sea animals shells and skeletons.
• Earth is 4.6 billion years old