Continental Drift

• Pangaea


  The large landmass that included all of Earth's present day continents

  
• Alfred Wegener was a German meteorologist and geophysicist who noticed the similarity in the coastlines of eastern South America and western Africa and speculated that those lands had once been joined together
• Continental drift


  One of the earliest ways geologists thought continents moved over time, as hypothesized by Alfred Wegener
• Wegener hypothesized that all of the modern-day continents had previously been clumped together in a supercontinent he called Pangaea

  
• Wegener brought together several lines of evidence to support his theory of continental drift
• Evidence of continental drift


  • Shape of the continents
  • Evidence from fossils
  • Evidence from landforms
  • Location of coal deposits
  • Evidence of climate
• Wegener's theory of continental drift was rejected because his explanation was too weak and clashed with widely accepted ideas at the time
• Alfred Wegener and his colleague Rasmus Villumsen died in a blizzard in Greenland in 1930
• Almost 50 years later, Harry Hess confirmed Wegener's ideas by using the evidence of seafloor spreading to explain what moved continents

  
• Seafloor spreading


  The continuous process of forming new igneous rock at midocean ridges by injection of magma that forms new seafloor
• Sonar uses sound waves to detect underwater objects and determine underwater landforms and distances
• Hess discovered the mid-Atlantic ridge and found the temperature near it was warmer, leading him to develop the theory of seafloor spreading
• The ocean floor is difficult to explore due to the deep darkness, cold water, and high water pressure
• The Earth does not get larger when new rock is added to the ocean floor at the mid-ocean ridge because the ocean floor is constantly being renewed
• Continental crust is primarily composed of granite, a light-colored igneous rock rich in silica and aluminum.
• Continental crust is thicker and less dense than oceanic crust, with an average thickness of about 35 km.