The Evolution of the Atmosphere - C1 AQA

1) The Earth's surface was originally molten for many millions of years. It was so hot that the atmosphere just 'boiled off' into space.

2) Eventually things cooled down a bit and a thin crust formed, but volcanoes kept erupting.

3) The volcanoes gave out lots of gas. We think this is how the oceans and atmosphere were formed.

4) The early atmosphere was probably mostly CO2 with virtually no oxygen. There may have also been water vapour, and small amounts of methane and ammonia- quite like the atmospheres of Venus and Mars today.

5) The oceans were formed when water vapour condensed.

1) Green plants and algae evolved over most of the Earth. They were quite happy in the CO2 atmosphere.

2) A lot of the early CO2 dissolved into the oceans. The green plants algae also absorbed some of the CO2 and produced O2 by photosynthesis.

3) Plants and algae died and were buried under layers of sediment, along with the skeletons and shells of marine organisms that had slowly evolved. The carbon and hydrocarbons inside them became 'locked up' in sedimentary rocks as insoluble carbonates (e.g. limestone) and fossil fuels.

4) When we burn fossil fuels today, this 'locked up' carbon is released and the concentration of CO2 in the atmosphere rises.

1) The build up of oxygen in the atmosphere killed off some early organisms that couldn't tolerate it, but allowed other, more complex organisms to evolve an flourish.

2) The oxygen also created the ozone layer (O3) which blocked harmful rays from the Sun and enabled even more complex organisms to evolve- us, eventually.

3) There is virtually no CO2 left now.