the evolution of the atmosphere

• phase 1 - first billion of years- surface was covered in volcanoes that erupted and released lots of gases, this is how the early atmosphere was formed
• the early atmosphere was mostly carbon dioxide, and virtually no oxygen
• volcano activity also released nitrogen which built up in the atmosphere overtime as well as water vapour and small amounts of methane and ammonia
• when the water vapour in the air condensed, it formed oceans.
• lots of carbon dioxide was removed from the early atmosphere as it dissolved in the oceans. The carbon dioxide then formed carbon precipitates that farmed sediments on the seabed
• green plants and algae evolved and absorbed some of the carbon dioxide so that they could carry out photosynthesis
• marine animals evolved. Their shells and skeletons contained carbonates from the oceans
• some of the carbon these organisms took in from the atmosphere and oceans became locked up in rocks and fossil fuels after the organisms died.
• when plants, plankton and marine animals die they fall to the sea bed and get buried by layers of sediment. over millions of years they become compressed and form sedimentary rocks, oil and gas- trapping the carbon within them and reducing carbon dioxide levels
• crude oil and natural gas are formed from the deposits of plankton
• coal is sedimentary rock made from thick plant deposits
• limestone is also a sedimentary rock mostly made of calcium carbonate deposits from the shells and skeletons of marine organisms
• green plants and algae also produce oxygen from photosynthesis
• algae evolved first - about 2.7 billion years ago , then green plants evolved
• as oxygen levels built up in the atmosphere overtime, more complex life evolved
• eventually the atmosphere around 200 million years ago reached a composition like today. 78% nitrogen 21% oxygen and small amount of other gases, many carbon dioxide, noble gases and water vapour (less than 1%)