Evidence suggests that originally the Earth's atmosphere contained a large amount of carbon dioxide and almost no oxygen. Our atmosphere is different today: it contains a large amount of oxygen, which is good, since we need it to breathe. What caused this atmospheric change? A) Global warming B) A meteor impact C) Photosynthetic organisms like cyanobacteria taking in carbon dioxide and releasing oxygen. D) Photosynthetic organisms like cyanobacteria taking in oxygen and releasing carbon dioxide.