The Origin of Atmospheric Oxygen by Joan Slottow

2.5 billion years ago earth’s atmosphere was devoid of oxygen and oxygen was toxic to life.  Then during the Siderian period of the Paleoproterozoic era, cyanobacteria, living in the shallow seas of that time, evolved the ability to perform oxygenic photosynthesis, producing oxygen molecules as a waste product and causing what is known as the Great Oxidation Event, revolutionary to life.  Today, in the Mammoth Hot springs area of Yellowstone National Park, hot water rises through limestone creating colorful terraces dripping with water.  The colors are created by a heat loving cyanobacteria, which in my imagination have produced the atmospheric oxygen.