The evolution of the atmosphere

• The atmosphere is made up of nitrogen, oxygen, argon, carbon dioxide and other gasses
• ~79% of the atmosphere is nitrogen, ~20% Oxygen with the other 1% being argon, carbon dioxide and other gasses
• ~0.04% of the atmosphere is CO2
• 4.6 billion years ago is when scientists first think the earth was made
• Earths first atmosphere was mainly made of CO2 with small amounts of water vapour, methane, ammonia, and nitrogen
• Earth was very hot in the early atmosphere and there was no plant or animal life mostly because of the composition of the atmosphere
• As the planet cooled down the water vapour condensed into the oceans ~2.7 billion years ago
• The small organisms that evolved once the oceans were formed were able to perform photosynthesis which releases oxygen gradually increasing the levels of oxygen in the atmosphere
• Carbon ends up in plants as they take it in during photosynthesis, this means that animals that eat the plants also end up ingesting and taking in the carbon
• Over millions of years dead carbon based organisms build up and are formed into sedimentary rocks like limestone (CaCO3)
• Over even longer periods of time some of the remains of carbon based life forms become fossil fuels like coal, crude oil and natural gas.
• Levels of ammonia and methane have reduced because they react with oxygen in the atmosphere
• Nitrogen is an unreacitve gas so has slowly built up in the atmosphere over time
• 5 bya- Atmosphere formed by volcanic activity - mainly CO2 with some H2O,N2, CH4 and NH3
• 4 bya - Earth cooled water vapour condensed and formed the oceans
• 3 bya - CO2 dissolved in oceans and taken in by organisms and eventually 'locked up' in sedimentary rocks and fossil fuels
• 2 bya - as plants evolved photosynthesis took in CO2 and produced O2 - gasses like methane (CH4) and ammonia (NH3) decreased as they reacted with oxygen - Nitrogen (N2) is very unreactive and has built up over time
• Today - Atmosphere mostly nitrogen and oxygen with small amounts of other gasses like water vapour, carbon dioxide and noble gases like argon, neon, xenon and krypton