Figure 26.1 Tectonic features of the ocean floor.

• oceanic trenches (cold, reverse faulting, older rocks)

• oceanic ridges (hot, normal faulting, younger rocks)

• all oceanic rocks are young (less than ca. 200 Ma)

• Harry Hess (1960) ==> Essay in Geopoetry

  
  
  Figure 26.2 Sea-floor spreading. Harry Hess proposed that upwelling of mantle material along the mid-ocean ridge system created new sea floor. The convective motion of mantle material carries the sea floor in a conveyor belt fashion to the deep-ocean trenches, where the sea floor descends into the mantle (from The Earth - An Introduction to Physical Geology (2nd ed.), by Tarbuck & Lutgens, Merrill Publishing Co., 1984).
  
  
  

• Fred Vine & D.H. Mathews (~ 1963)

  
  
  Figure 26.3 How the sea floor becomes a magnetic tape recording of its development.
  
  
  
  
  Figure 26.4 Sea floor ages distributed about the spreading ridges.
  
  
  
  
  Figure 26.5 Geomagnetic time scale (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).