How did Earth come to have an oxygen atmosphere?A.Precambrian rocks released oxygen into the atmosphere.B.Volcanoes released oxy
gen into the atmosphere.C.Early organisms created oxygen from other gases in the atmosphere.D.Oxygen was the primary gas originally in Earth's atmosphere.
Oxygen was first produced via photosynthesis as ocean microbes evolved in the event that was called the Great Oxidation Event. Therefore the correct answer is C
