The atmosphere is made up of about:
- 78% nitrogen
- 21% oxygen
- Small amounts of other gasses like carbon dioxide, water vapour and noble gasses
It’s been this way for about 200 million years….but some have a theory that this is what happened before:
First Billion Years Of The Earth – Lots Of Bloody Volcanoes
During the first billion years of the Earth’s existence there was intense volcanic activity. This activity released the gases that formed the early atmosphere and water vapour that condensed to form the oceans.
One theory suggests that during this period the Earth’s atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas (like the atmospheres of Mars and Venus today). There may also have been water vapour and small proportions of methane and ammonia.
The Next Phase – Plants To The Rescue
Plants and algae started to evolve and eventually covered most of the earth.
Lots of the carbon dioxide in the air was dissolved into the oceans, but also the plants and algae absorbed some of it and produced oxygen (through photosynthesis).
The plants and algae gradually died and were buried under layers of sediment with marine organisms that had started to evolve. The carbon and hydrocarbons they contained for locked up in sedimentary rocks as insoluble carbonates (like limestone) and fossil fuels.
If today we burn these fossil fuels we release this locked carbon and the amount of carbon dioxide in the atmosphere starts to rise again.
The Latest Phase – Things Get Nice
Not all the organisms around in the phase above liked the oxygen that was increasing in the atmosphere and died off – but more complex organisms like us were able to evolve based on breathing oxygen.
An ozone layer was also created blocking lots of harmful rays from the sun and allowing even more complex organisms to evolve.
There is now not much carbon dioxide left.