Earth Science: The Story of oxygen

At present, the Earth's atmosphere contained in gas, about four-fifths nitrogen and one-fifth of the oxygen. In which the formation of nitrogen, mostly from the non-biological role of inorganic processes, and nitrogen in the atmosphere of the residence time may be as long as billions of years old. By comparison, the oxygen is produced mostly from the use of solar energy by biological oxidation, as oxygen in the atmosphere of the residence time, it is only a short span of four million years. Even so, in the past 500 billion years, the atmospheric oxygen content, or can be as high as 10% to 30%.



As a result of photosynthesis, by 12, composed of carbon dioxide, make it easier to participate in reaction (compared to 13 by the composition of carbon dioxide), but respiration will also be a product of photosynthesis reaction swap would re-release of carbon 12 Back to the atmosphere. Thus, when more than photosynthesis, respiration, the increasing number of carbon 12 to be used into organic substances, the atmosphere of the relative content of carbon-13 will begin to increase. Therefore analysis of the early Earth's carbon 12 and carbon 13 ratio, the Earth could be the possibility of oxygen content at the time.



Although as early as 220 billion years ago, oxygen began to accumulate in the atmosphere, but at the time of oxygen content in the atmosphere, only about 1 percent today. Until now about 750 million with the new inter- 550 billion years native yuan (Neoproterozoic), as well as about 360 million years ago to between 300 billion years carbon Ji Shi (Carboniferous) period of time before there were a large number of emerging oxygen event.



Primary element in the new period, a large single-celled eukaryotic algae - plankton began to appear, they greatly speed up the organic material was buried in marine sediments to the process of respiration to reduce the consumption of oxygen, making oxygen content in the atmosphere in the rapid accumulation, but also led to a large number of Cambrian species phenomenon. Shi Ji-carbon period is due to the appearance of large numbers of terrestrial plants, oxygen content in a large number of accumulated again to the atmosphere, even up to as much as 30% ratio.



At the end of the Triassic, a bio-mass extinction occurred at the same time, oxygen content is also reduced to 10% ~ 12% level. And then in the past two million years, the oxygen content and then it slowly accumulated to the extent of 23 percent. To this day, was buried as a result of biological oxidation rate and speed are gradually be controlled, making the oxygen content is no longer marked a dramatic fluctuations.