Earth Structure + Composition

• Earth's Structure

  • Core
  • Mantle
  • Lithosphere
  • Crust

  
• The Geologic Cycle


  Rock Cycle—Igneous, Sedimentary, Metamorphic

  
• Plate Tectonics

  • Sea-Floor Spreading
  • Subduction
  • Plate Boundaries
• Earth congealed from a nebula, ~4.6 billion yrs
• Gravity sorted the dust, gas, (icy) comets into concentric circles with the core being the heaviest and the crust being the lightest
• Core


  • 1⁄6 of volume, ⅓ of mass
  • Inner core is solid iron
  • Outer core is molten iron
  • Generates magnetic field that protects from solar wind/cosmic radiation
• Lower & Upper Mantle


  • 80% earth's volume
  • Probably contain lots of water (in the crystalline structure)
  • Contains "hot spots" like Hawaii & other volcanic chains
• Lithosphere


  Uppermost mantle + crust
• Crust


  • Oceanic = 5 km
  • Continental = 20–60 km

  
• Continental Crust


  • Granite
  • Crystalline
  • Low density (2.7 g/cm3)
• Oceanic Crust


  • Basalt
  • Granular
  • High density (3.0 g/cm3)

  
• Crust "floats" on denser layers below
• Geologic Cycle


  1. Being formed by endogenic (internal) processes

  2. Worn down by exogenic (external) processes
• Mineral


  Inorganic, non-living, natural compound with chemical formula & crystalline structure
• Rock


  Assemblage of minerals, mass of a single mineral, or solid organic material
• The Rock Cycle


  1. Igneous

  2. Sedimentary

  3. Metamorphic
• Igneous Rocks


  • Solidify from cooling magma or lava
  • Magma is molten rock beneath the surface (intrusive)
  • Lava is molten rock at the surface (extrusive)
• Intrusive Igneous Rocks


  • Slower cooling leads to larger crystals
• Extrusive Igneous Rocks


  • Faster cooling leads to smaller crystals
• Sedimentary Rocks


  Formed from the cementation, compaction, and hardening of sediments
• Sedimentary Rocks


  • Sandstone
  • Shale
  • Limestone
  • Coal
• Metamorphic Rocks


  Formed from the physical and chemical transformation of igneous or sedimentary rocks due to extreme pressure and heat
• Metamorphic Rocks


  • Gneiss
  • Slate
  • Marble
  • Quartzite
• Plate Tectonics


  • Changes in the configuration of the earth's crust due to internal forces
  • Upwelling of magma
  • Sea-floor spreading and subduction
  • Plate movements
• Continental Drift Theory


  • Proposed by Alfred Wegener in the early 1900s
  • Suggested there was once a single "super continent" called Pangaea that floated on the oceanic crust
• Evidence of Continental Drift

  • Continents fit together like a jigsaw puzzle
  • Fossils match across oceans
  • Rock types and mountain ranges match across oceans
  • Climate Evidence (Glacial Deposits)

  
• Plate Boundaries

  • Spreading boundary - crust is being pulled apart
  • Converging boundary - one plate is subducted beneath another
  • Transform boundary - two plates glide adjacent to each other
• Divergent Plate Boundary


  New crust being created, most associated with mid-ocean ridges

  
• Convergent Plate Boundary


  Continental and oceanic crust collides, produces subduction zones, trenches, volcanoes (mountains), zones of compression and crustal loss

  
• Transform Plate Boundary


  Plates slide past one another, rock of different types and ages may be found on opposite sides of the boundary
• Hot Spots


  Areas on Earth that exist over a mantle plume, upwelling material from the mantle, occur beneath both continental and oceanic crust, some are fixed, others move
• Plates move 1-10 centimeters per year (≈ rate of fingernail growth)