How has oxygen on earths atmosphere changed over time?
Earth’s atmosphere originally did not have much O2 in it. You might want to look up the Urey-Miller experiment of 1952 where they put H2O (water), methane (CH4), CO2, and NH4 (ammonia) in a flask, shot electrical discharges through the gas mixture to simulate lightening, and produced amino acids, including the amino acids that are the building blocks of DNA. Oxygen didn’t start building up in the atmosphere until cyano-bacteria in blue green algae started to photosynthesize sunlight and release oxygen as a waste product. “… Certain processes were essential to the development of the earliest cellular life,” added Raymond, “and the most basic, intrinsic reactions organisms need to survive persist today. For example, how we break down glucose (sugar) has been remarkably well conserved for billions of years.” For higher life forms to evolve, however, additional processes were needed, such as the ability to synthesize, or break down, steroids and alkaloids and those require oxygen. But un
