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- 4.6 billion years ago the surface of earth was covered in volcanoes, erupting and releasing gases. We think this is how the early atmosphere was formed.It was mostly made up of carbon dioxide, with almost no oxygen.Volcanic activity also released nitrogen, which built up over time, as well as water vapour, and small amounts of methane and ammonia.
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- When the water vapour in the atmosphere condensed, it formed the oceans. Lots of carbon dioxide was removed from the early atmosphere as it dissolved in the oceans. This then reacted to form carbonate precipitates that formed sediments on the seabed.
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- Algae evolved around 2.7 billion years ago and absorbed some of the carbon dioxide so they could carry out photosynthesiscarbon dioxide + water -(light)- glucose + oxygenOver the next billion years or so, green plants also evolved.As oxygen levels built up in the atmosphere over time, more complex life (like animals) could evolve.
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- When marine animals evolved, their shells and skeletons contained some of the carbonates from the oceans. They formed deposits on the seabed when the organisms died, getting buried by layers of sediment.
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- Over million of years, this become compressed and formed; sedimentary rocks, oil, coal and gas - trapping the carbon within them - helping to keep it out of the atmosphere - this is why they are called 'fossil fuels'.
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- Around 200 million years ago, the atmospere reached a composition similar to how it is today;80% Nitrogen20% oxygensmall amounts of other gases, mainly carbon dioxide, noble gases and water vapour
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