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Oxygen on the Earth

Question: Why does oxygen only exist on the Earth?

Answer:

Actually it is not quite right. It is true that plants take in carbon dioxide and give out oxygen and that we breathe in oxygen and breathe out carbon dioxide.
However it is quite possible that there was some oxygen in the atmosphere of the planet when the planet was young and before plants developed.
Also oxygen does not only exist on the Earth. Even if we ignore all the planets in the Universe that we do not know about oxygen has been detected in our Solar System.
Admittedly there is not much but here are some figures that might interest you:

Mars atmosphere
Carbon dioxide 95.32%
Nitrogen 2.7%
Argon 1.6%
Carbon monoxide 0.07%
Oxygen 0.03%

Venus atmosphere
Carbon dioxide over 96%
Nitrogen 3%
Minute traces of oxygen, sulphur dioxide, water vapour etc.

Whether or not a planet can "hang on" to its atmosphere depends on the escape velocity of the planet.

 

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© Keith Gibbs 2020