ESS220
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)