Term Papers on Gaia And Plate Tectonics

Term Paper Title	Gaia And Plate Tectonics
# of Words	1237
# of Pages (250 words per page double spaced)	4.95

Gaia and Plate Tectonics

     Geologists and biologists have traditionally thought of life as having adapted to
     changes in the environmental conditions over time, but a new view of the earth derived
     from the Gaia theory has emerged.  Many scientists now look at the entire earth as an
     organism, where living and nonliving matter evolve together maintaining an environment
     nearly ideal for life.  The Gaia theory maintains that soon after the formation of
     life, and organisms began to change the environment, and as well as adapt to this
     environment.  One example of Gaian regulation is in the earth's maintenance of a
     relatively constant atmospheric temperature since life begun.  While the sun now gives
     off 30 percent more heat to the earth compared to four eons ago. The earth's global
     temperature has remained relatively constant.  One regulator in reducing global
     temperature is the conversion of carbon dioxide and water in the presence of light into
     carbohydrates and oxygen.  As the amount of light reaching the earth has increased, the
     rate of photosynthesis increased, thereby removing CO2 and cooling the planet.  Another
     regulator is the storage of CO2 in calcium carbonate in the shells of limestone
     producing organisms.  This control of global temperature has been critical in Gaian
     regulation of the planet. (Anderson,348) Another example of how the earth and the
     biosphere may have evolved is in its dependence and possible influence on plate
     tectonics.  It's fairly obvious that plate tectonics has a great effect on the biota,
     but the hypothesis that the biota has altered plate tectonics is still in its infancy.
     Some scientists believe that plate tectonics can only occur on a planet that has a
     moderate surface temperature.  High surface temperatures, such as those found on Venus,
     "favor the development of a thick, buoyant crust." ( Stolz,50 ) For plate tectonics to
     work, the plates must be thin enough and dense enough to break and subduct.  If this is
     indeed true, then it also must be true that life has an influence on plate tectonics.
     If today's carbon dioxide levels were comparable to the levels before life became
     abundant, then we would have a significantly warmer surface temperature, possibly warm
     enough to prevent plate tectonics.(Stolz,77) The impact of life on plate tectonics,
     although speculative, would probably be significant.  Without life on earth, the
     atmospheric composition would be approximately 98 percent CO2, roughly the same as is
     on Venus.  The presence of large amounts of CO2 in the atmosphere four billion years
     ago was necessary to prevent the oceans from freezing through, but if this level of
CO2 was present in today's atmosphere, the increased insolation would bring the atmospheric
temperatures to 290° F., or 50° C.,  and causing the oceans to boil away and making the
planet forever dry, being comparable to Venus.

       It has often been suggested that life originated on the earth because of a
       coincidence between the narrow temperature interval over which water is liquid and
       the temperature extremes that actually occur on the earth.  The earth apparently is
       also exceptional in having active plate tectonics.  If the carbon dioxide in the
       atmosphere of Venus could turn into limestone, the surface temperatures and those in
       the upper mantle would drop.  The basalt-eclogite phase change would migrate to
       shallow depths, causing the lower part of the crust to become unstable.  Thus there
       is the interesting possibility that plate tectonics may exist on the earth because
       limestone-generating life evolve  here. (Nisbet,54)

     The primary reason limestone forming organisms are sometimes credited with allowing
     plate tectonics to occur on Earth is that they consume carbon dioxide, converting it to
     calcium carbonate in their shells.  When th...

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