04. Geology and Earth Resources

• Earth


  • Dynamic planet, constantly changing structure
• Layers of Earth

  • Core
  • Mantle
  • Crust

  
• In 1855, Antonio Snider published a sketch showing how the two continents could fit together, jigsaw-puzzle fashion
• Climatologist Alfred Wegener was struck by the matching coastlines and geologic evidence from the continents
• Sedimentary rocks may preserve evidence of the ancient climate and fossil remains of ancient life
• Evidence in sedimentary rocks

  • Extensive glaciation in now-tropical places
  • Desert sand deposits in now-moist, temperate regions
  • Jungle plant remains in now-cool places
  • Coal deposits in Antarctica
• The distribution of fossils like Glossopteris and Mesosaurus was part of the evidence Wegener cited to support his continental-drift hypothesis

  
• Pangaea


  The single supercontinent that Wegener proposed had split apart
• Most people had difficulty visualizing how continents could "drift" around on a solid earth
• Plate tectonics


  The broader theory encompassing continental drift, relating deformation to the movement of rigid plates over a weaker, more plastic layer in the earth's upper mantle

  
• Types of plate boundaries

  • Divergent
  • Convergent
• Divergent plate boundary


  Lithospheric plates move apart, releasing pressure and allowing magma to well up, resulting in volcanic activity and earthquakes

  
• Divergent plate boundaries


  • Seafloor spreading ridges
  • Continental rifting

  
• Continental rifting can lead to the formation of a new ocean basin if it continues

  
• Examples of continental rifting


  • Afar Depression in Ethiopia
  • Rio Grande Rift
  • New Madrid Fault Line

  
• Convergent plate boundary


  Plates are moving toward each other, with one plate being subducted beneath the other, resulting in volcanic activity and earthquakes

  
• Types of convergent plate boundaries

  • Ocean-ocean
  • Ocean-continent
  • Continent-continent

  
• Subduction zones balance the seafloor equation, as new oceanic lithosphere created at spreading ridges is consumed

  
• Volcanoes form where molten material rises up through the overlying plate to the surface at convergent boundaries
• Continent-continent collisions create a great thickness of continental lithosphere, as seen in the Himalayas

  
• Most often, the sea floor in a zone of convergence is subducted and destroyed
• All continents are part of moving plates, sooner or later they all are inevitably transported to a convergent boundary, as leading oceanic lithosphere is consumed

  
• If there is also continental lithosphere on the plate being subducted at an ocean-continent convergent boundary, consumption of the subducting plate will eventually bring the continental masses together

  
• Sooner or later, a continental mass on the subducting plate meets a continent on the overriding plate, and the resulting collision creates a great thickness of continental lithosphere, as in the Himalayas

  
• The two landmasses collide, crumple, and deform. One may partially override the other, but the buoyancy of continental lithosphere ensures that neither sinks deep into the mantle, and a very large thickness of continent may result

  
• Earthquakes are frequent during continent-continent collision as a consequence of the large stresses involved in the process. The extreme height of the Himalaya Mountains is attributed to just this sort of collision
• India was not always a part of the Asian continent. Paleomagnetic evidence indicates that it drifted northward over tens of millions of years until it "ran into" Asia and the Himalayas were built up in the process
• Many major mountain ranges worldwide represent sites of sustained plate convergence in the past, and much of the western portion of North America consists of bits of continental lithosphere "pasted onto" the continent in this way

  
• A close look at a mid-ocean spreading ridge reveals that it is not a continuous rift thousands of kilometers long. Rather, ridges consist of many short segments slightly offset from one another
• Transform fault


  A special kind of fault, or break in the lithosphere, where the opposite sides belong to two different plates moving in opposite directions
• As the plates scrape past each other, earthquakes occur along the transform fault. Transform faults may also occur between a trench (subduction zone) and a spreading ridge, or between two trenches, but these are less common
• The famous San Andreas Fault in California is an example of a transform fault
• Mineral


  A naturally occurring, inorganic, solid element or compound with a definite chemical composition and a regular internal crystal structure
• Naturally occurring, as distinguished from synthetic, means that minerals do not include the thousands of chemical substances invented by humans
• Inorganic, means not produced solely by living organisms or by biological processes
• Solid means that the ice of a glacier is a mineral, but liquid water is not
• Chemically, minerals may consist either of one element—like diamonds, which are pure carbon—or they may be compounds of two or more elements
• Minerals are crystalline, at least on the microscopic scale
• Crystalline materials


  Solids in which the atoms or ions are arranged in regular, repeating patterns
• Identifying characteristics of minerals

  • Chemical composition
  • Crystal structure