Biogeochemical Cycles

Along with the circulation of the atmosphere and oceans there are energy and mass circulating through and interacting with the various life subsystems of Earth. The corporate name for these translocations is biogeochemical cycles. The term is apt in that it connotes the interplay of life and its chemical environment on, over and under Earth’s landscapes. In toto, the magnitudes of these flows are unimaginably vast and complicated but their components have been studied to the extent that the basics are well known. The cycles provide needed supplies of mass energy because these commodities are finite on our planet. In short, the biogeochemical cycles bathe the planet in ways that provide for sustained life. Although it can be shown that humans have had major, unintentional impacts of some of these cycles, it is evident that there is much resilience in the way they function.

The energy cycle is usually the first to be noted because it is the fuel by which all the other cycles act. A huge amount of solar energy is incident on the Earth system. Instantaneously, the amount is about 174 petawatts (1015 watts), which is billions of times the rate of electric energy generated by human devices. As solar energy passes through the atmosphere there are all manner of pathways as described elsewhere.

The key energy for life is supplied by photosynthesis. Although incredibly complex with many nuances yet to be understood, photosynthesis is responsible for energizing the large bulk of biomass on the planet and, ultimately, is the source of energy on which the human organism depends. Photosynthesis occurs in plants and uses carbon dioxide and water commonly available in the environment. Not all solar energy received is used. Perhaps 0.6 percent of solar energy incident on Earth’s surface interacts with the above ingredients in plant cells through the auspices of the green pigment chlorophyll. The radiant solar energy is converted into chemical form as a series of carbohydrates. This storage allows plants a steady supply of energy for respiration, the processes that keep the plant alive. Of incredible importance to our planet is the oxygen released as a byproduct; the bulk of our atmospheric oxygen supply was produced by photosynthesis.