Chemistry AQA Chapter 9

 Evidence for the early atmosphere is limited because of the time scale of 4.6 billion years.

• intense volcanic activity that released gases that formed the early atmosphere consisting of mainly carbon dioxide with little or no oxygen gas
•  water vapour realeased condensed to form the oceans

• When the oceans formed carbon dioxide dissolved in the water reducing the amount of carbon dioxide in the atmosphere

• Volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia.

• Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis

• Algae first produced oxygen about 2.7 billion years ago soon after this oxygen appeared in the atmosphere

• the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve.

• Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.

• Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon.

• Greenhouse gases in the atmosphere maintain temperatures on Earth

• The sun radiates energy and some is transferred to earth

• most this energy is absorbed by earth's surface (having warming effect) but some is reflected back into space by earth's surface or gasses in earth's atmosphere

• the earths surface cools by emitting infared radiation

• some radiation is absorbed by greenhouse gases and radiated back to earth surfaces