OCR Gateway Chemistry - C1: Clean Air

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Clean Air

The Earth’s atmosphere consists of a mixture of gases surrounding the planet. Gravity prevents the gases from escaping into space.

The current atmosphere consists of 78% nitrogen, 21% oxygen, 0.035% carbon dioxide and 0.965% other gases such as water vapour and argon.

The Earth is approximately 4.5 million years old and so there is no record of how it was formed. One theory involves volcanoes and plants. The large amount of volcanic activity produced huge volumes of gas, most likely water vapour and carbon dioxide with small proportions of ammonia and methane.  The water vapour condensed to form oceans, leaving an atmosphere with high levels of carbon dioxide. There was little to no oxygen in the early atmosphere.

The process of photosynthesis uses carbon dioxide from the atmosphere and releases oxygen. As plants evolved, photosynthesis reduced the amount of carbon dioxide and increased the level of oxygen in the atmosphere.

Carbon dioxide is a soluble gas and so large amounts were dissolved into the oceans. It was used by marine


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