Hallam, Ch. 5: Age of the Earth

 

Terms

As you read this chapter, watch for and define the following terms.

     

     

  1. Denudation

     

  2. Nebular hypothesis

     

  3. Thermal gradient

     

  4. Steady-state

     

  5. Tidal friction

     

  6. 'New Uniformitarianism'

     

  7. Planetisimal hypothesis

     

  8. Pleochroic haloes

     

  9. Phanerozoic

     

  10. Methodological uniformitarianism

     

  11. Substantive uniformitarianism

     

  12. Neo-catastrophism

     

  13. Channelled scablands

     

  14. Punctuated equilibrium

Focus Questions

     

     

  1. Explain the significance of Darwin's account of the denudation of the Weald.

     

  2. Describe three arguments Lord Kelvin employed to argue against a Lyellian vision of the past.
       
    • How did Kelvin attempt to establish a maximum age of the earth equal to about what Darwin required for the denudation of the Weald?

       

    • How did Kelvin's arguments rely on the Laws of Thermodynamics?

       

    • On what qualifying assumptions did Kelvin's arguments depend?

     

  3. How did the "independent estimates" of the age of the earth compare to Kelvin's estimates? Were these estimates truly independent and mutually collaborative?

     

  4. Describe the epistemological and conceptual relationships between geology and physics. Illustrate by citing responses of various geologists to Kelvin's arguments. Consider the eventual opposition mounted to Kelvin's views prior to the discovery of radioactivity (Croll, Fisher, Geikie, Chamberlin, et al.).

     

  5. How did the discovery of radioactivity undermine Kelvin's estimates of the age of the Earth?

     

  6. Explain the process of radiometric dating.
       
    • Define half-life, decay constant, pleochroic halo, alpha particle, isotope.

       

    • Explain the significance of stony meteorites for geological dating.

     

  7. Explain how it is that Hallam argues that Lyell's uniformitarianism was correct in one sense and misguided in another. Do you agree with Hallam's assessment?

Further Reading