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Physics 20 Online
OpenStudy (anonymous):

Why is Earth's atmosphere rich in oxygen and poor in carbon dioxide, whereas the reverse is true on Venus?

OpenStudy (jamesj):

The earth didn't always have an oxygen rich atmosphere. But around 2.4 billion years ago, plants started to produce a great amount of free oxygen which changed the atmosphere. http://en.wikipedia.org/wiki/Great_Oxygenation_Event

OpenStudy (anonymous):

thanks

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