It would seem that an introduction to oxygen is unnecessary, for we deal with it and depend upon it every moment of our lives. Oxygen is to us the essential stuff of the air we breathe. We are aerobic animals who obtain energy by oxidizing foodstuffs. As such, we are wholly dependent on oxygen for life – go without it for a couple of minutes and we panic and may even suffer irreversible brain damage. In a few more minutes, we perish. Animal metabolism depends upon oxygen for almost all of its energy-generating processes. Yet this was not always so. Early in the history of the Earth,.
