The Way of Science

An Introduction To Wegener, Continental Drift, and Plate Tectonics

In all the sciences, one goal - a "holy grail," so to speak - is the formulation of broad, powerful, predictive explanations for the phenomena and structures of the Universe. As you know already, these are variously called "synthetic theories" or "models." In physics, where we have a long history of investigation, the number of such theories is large. Remember the kinetic theory of gasses? That's one. There is also thermodynamics, and relativity (both to be covered later), and many other powerful explanations. In chemistry, there are the atomic theory and the molecular orbital theory to explain the nature of the basic building blocks of the Universe and how they are bonded to each other. Biology has its "grand unifying theory," the Modern Synthetic Theory of Evolution, which began with Darwin's publication (1859) of On the Origin of Species by Natural Selection. In the 1960s, geology finally developed and accepted the theory of Plate Tectonics, and it has shown to be as powerful as the Synthetic Theory of Evolution. Consider how many different aspects of the Earth's history, processes, and structures are determined or strongly influenced by movements in a liquid outer core transmitted to crustal plates via a slowly flowing mantle (all these terms will become clear soon):

• large chunks of crust, including continents, move vast distances over geologic time. Continents split. Continents collide. Oceans appear and disappear. Mountains and volcanoes are produced, as are earthquakes.
  
  
• the Earth's magnetic field is generated. That's very important, and we will return to it later, with details.

These are some of the more obvious results of core/mantle/plate movements. Less direct and less obvious but enormously important are the following:

• major shifts in ocean currents occur, and sea levels change radically. Vast and major climate changes are produced, resulting in ice ages and global warming.
  
  
• bursts of biological Evolution are stimulated, including both production of many new species and mass extinctions.

Required readings:

     1. (Text) Hazen and Trefil, Science Matters, Chapter 13, The Restless Earth, pp.174-190.

     2. (Film) Earth Revealed, Parts 5, 6: Birth of a Theory, Plate Dynamics. These will be shown at night; see schedule.

Recommended readings:

Following two articles are optional. They are not required, but strongly recommended.

     3. (#8) Hallam, A.1975. Alfred Wegener and the Hypothesis of Continental Drift. Scientific American 232(2): 88-97.

     4. (#9) Hurley, P. 1968. The Confirmation of Continental Drift. Scientific American 218(4): 52-62.