Answer the following question given this paragraph: 

Oxygen has increased in the atmosphere throughout the history of the earth. Note the logarithmic scale, which indicates great increases after first photosynthesis (in bacteria) and then land plants evolved. Related geological events: A = no oxidized iron; B = oxidized iron bands in seabed rock - evidence for O 2 in the oceans; C = oxidized iron bands on land and ozone layer formation- evidence for O 2 in the atmosphere.


Q: What has increased in the atmosphere throughout the history of the earth?


A:
oxygen