Oxygen level life cycles

The TCA cycle can be regarded as the biochemical pathway that is of paramount importance to all aerobic organisms. Since it evolved about three billion years ago as a direct consequence of a significant rise in atmospheric oxygen levels, life on earth made an unprecedented evolutionary quantum leap. 

Industries, especially those that generate electric power, use a tremendous amount of water to cool steam and condense it back to water. This water is normally taken from a lake or stream, used in the cooling process, and then returned to the same body of water. If the heated water is returned directly to the lake or stream, the increase in temperature may cause the oxygen levels to decrease below those required for the survival of certain types of fish. The increased temperature may also trigger or repress natural cycles of aquatic life, such as spawning. 

If oxygen is produced by the reduction of carbon dioxide, then atmospheric C02 levels must have declined over the life of the Earth, and there is evidence that this has indeed occurred.The climatic implications of changes in atmospheric C02 levels and how the global carbon cycle operates are addressed in Chapter 6, after the various elements of the carbon cycle have been introduced in the intervening chapters. For the moment, we continue with a more detailed look at the evolution of life in terms of the organisms that are most important by way of their contributions to the organic matter that is eventually buried in sedimentary rocks. 

Fig. 9.14. Relative distribution of overcharge current as a function of VRLA saturation level between H2 evolution/H20 decomposition/grid corrosion and the oxygen cycle throughout cycle-life.

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