ESS5
Prof. Jin-Yi Yu
Where Did O2 Come from?
q Photosynthesis was the primary process to increase the amount of oxygen in the atmosphere.
čPrimitive forms of life in oceans began to produce oxygen through photosynthesis probably 2.5 billion years ago.
čWith the concurrent decline of CO2, oxygen became the second most abundant atmospheric as after nitrogen.
(from Earth’s Climate: Past and Future)