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Earth’s atmosphere has undergone significant changes over 4 billion years. Initially dominated by water vapor, carbon dioxide, and trace gases like methane and ammonia, it transformed as plants evolved, releasing oxygen. This shift polluted the atmosphere with oxygen, allowing the formation of an ozone layer that protects against harmful UV radiation. Over the last 200 million years, the atmosphere has stabilized to roughly 80% nitrogen and 20% oxygen, with small amounts of other gases. This evolution has enabled diverse life forms to flourish on our planet.
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Volcanic activity 4 billion years ago Water vapour condenses to form oceans Mainly carbon dioxide Some methane, ammonia and water vapour Plants evolve 3 billion years ago Plants give out oxygen – atmosphere polluted by oxygen Carbon & carbon dioxide taken in by sedimentary rocks as carbonates and fossil fuels Methane & ammonia react with oxygen – some nitrogen produced Nitrogen produced by organisms including denitrifying bacteria Micro-organisms that cannot tolerate oxygen killed off 2 billion years ago Oxygen results in ozone layer Ozone layer filters out harmful ultra violet light This allows evolution of new organisms 1 billion years ago Atmosphere for the past 200 million years: 80% Nitrogen 20% Oxygen Now Small amounts of other gases including water vapour, carbon dioxide, noble gases
