The Gaian Theory Essay, Research Paper
Introduction
Continental drift is the theory that the positions of the earth’s continents have moved considerable distances throughout geologic time. A German meteorologist, by the name of Alfred Wegener, proposed the first comprehensive theory of continental drift in 1912. He based it on the way the continents fit together on the opposing Atlantic coasts as well as the paleontology correlation on both sides of the Atlantic. The theory he proposed, stated that, 200 million years ago there was one large continent, or supercontinent, called Pangaea; Pangaea split into two large landmasses called, Laurasia and Gondwanaland.(Plummer 460)
During the Mesozoic era, Laurasia and Gondwanaland broke apart in some areas and drifted further away from their previous positions In this process, the Earth’s rotation caused horizontal alterations in the granite continents floating on the sea of the basaltic ocean floors. The frictional drag along the leading edges of the drifting continents created mountains. Wegener’s theory met controversy until 1954, when British geophysicists seeking to explain the phenomenon of polar wandering revived it. (Plummer 460)
Around the same time that geologists were again becoming interested in the idea of moving continents, a geologist at Princeton University, by the name of Harry Hess came up with the theory of sea floor spreading in 1962. Hess’s theory states that the sea floor moves away from the mid-oceanic ridge as a result of mantle convection. This theory clearly contrasted with Wegener’s early theory of continental drift, except for Wegener believed that the sea floor remained stationary while the continents moved through it. In the late 1960’s the theory of Plate Tectonics evolved from the two
preexisting ideas of continental drift and sea floor spreading.(Plummer 465)
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 has emerged from what is now called the Gaia theory. 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.
Gaia and Plate Tectonics Working Together
The Gaia theory maintains, that soon after the formation of life, organisms began to change the environment, as well as adapt to the environment. One example of Gaian regulation is in the earth’s maintenance of a relatively constant atmospheric temperature since life began. The Earth’s global temperature has remained relatively constant considering the sun gives off 30 percent more heat to the earth compared to four eons ago. 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)
One more 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 ) In order for plate tectonics to work, the plates must be thin enough and dense enough to break and subduct. For this to be 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.. The atmospheric composition would approximately be 98 percent CO2, if the earth were barren of any life forms. That is roughly the same as on Venus. The presence of large amounts of CO2 in the atmosphere four billion years go was necessary to prevent the oceans from freezing through. However, if this level of CO2 were present in today’s atmosphere, the increased insulation would bring the atmospheric temperatures to 290. F., or 50. C.; 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 evolves 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 the organisms die, the shells sink to the bottom of the ocean and are gradually buried. Eventually, some of the carbon dioxide is returned to the atmosphere through volcanic activity, but the net effect is a reduction in carbon dioxide in the atmosphere. There is no observation or experiments to support this, but there is one other hypothesis that states that the weight of these organisms, mostly stromatolites, depressed the oceanic crust sufficiently to cause subduction. This seems rather unlikely, however, and unless more evidence is gathered supporting this hypothesis, it will probably never be taken seriously.(Stolz,39)
The presence of water in the liquid state is also vital to plate tectonics as well as life. Water plays an important role in plate tectonics in that as magma rises, water permeates the pores of the solidifying rock. This happens at such a rate that, on the modern Earth, a volume of water roughly equivalent to the total volume of the oceans passes through the new lava about once every ten million years; which is a relatively short time, geologically speaking. In the distant past, the rate of cycling known as hydrothermal circulation, was probably much greater.(Westbroek,322) This process is significant to both plate tectonics and life, as the water in the rock helps the rock to melt again at a lower temperature, and it controls the chemistry of the water. These facts suggest that if plate tectonics were not active, the oceans might have become too toxic to support life.(Lovelock,134)
Conclusion
This information clearly states that there is some type of relationship between life and plate tectonics. There is the indication that a primitive plate tectonics was in effect before Gaian regulation began, but there is significant evidence that life has kept the process going. It seems that the presence of life, and the high surface temperature would cause the crust to gradually thicken and become more buoyant, thereby making subduction unlikely. Likewise, without plate tectonics the land would have become sterile and the oceans may have become toxic, thus probably preventing the continual existence of life on Earth.(Ages 1991)
It’s difficult, if not impossible, to separate the argument of how life effects plate tectonics from the argument of how plate tectonics affects life. One can imagine what the earth might be like if plate tectonics were not active here. Pangea was probably relatively featureless, and if the earth’s crust were stationary, it would undoubtedly remain flat. In addition, weathering and erosion would quickly bring the continent to sea level, and eventually the tides would disperse the sediment across the ocean floor (Perhaps like an Atlantis effect). The absence of plate tectonics would tremendously affect life on earth. There is a good chance that life could have formed in the oceans in the absence of plate tectonics, but it might not have persisted. It is doubtful that life would ever have been able to survive on land. The actions of weathering and erosion, constantly washing vital nutrients into the sea, and a lack of some kind of mechanism for returning those nutrients back to the land, the rock would become incapable of supporting life.
Works Cited
Anderson, Don L. The Earth as a Planet: Paradigms and Paradoxes. Science. January,
1984): 347-354.
Lovelock, James E.. Gaia: A New Look at Life on Earth. Oxford: Oxford University
Press, 1979.
Nisbet, E. G. Living Earth: A Short History of Life and Its Home. New York:
Harper Collins Academic, 1991.
Plummer, Charles C., McGeary, David, Carlson, Diane H.. Physical Geology Eighth Edition. McGraw-Hill.1999. 460-492
Stolz, John F. Biomineralization and Gaia Scientists on Gaia. Cambridge: The MIT
Press, 1991.
The Ages of Gaia: A Biography of Our Living Earth. New York: Bantam Books, 1988.
Westbroek, Peter. Life as a Geological Force: Dynamics of the Earth. New York: W. W.
Norton and Company, 1991.