Throughout time, rising oceanic and atmospheric oxygen levels have been crucial to the habitability of environments at the surface of the Earth. "The Earth had no free oxygen gas in its atmosphere early on," said Ellen Thomas, the Harold T. Stearns Professor of Integrative Sciences. "The oxygen has been provided over time by photosynthesis of algae followed by storage of organic matter in rocks." Thomas, who also is research professor of earth and environmental sciences, examines the timing of oxygen formation in Earth's atmosphere and oceans over geological time in a study published in the May 2018 issue of Science.…