Formation and Layers

• process of earth accretion:

  1. clump of dust grains accumulate
  2. clump of dust forms planetesimals
  3. force of gravity attract planetesimals into accumulatin
  4. planetisimals form protoplanet
  5. final step: differentiation of earth - heavy/dense materials like nickel and iron sink to the center of the earth; light/dense materials rise to the surface
• crust - outermost layer; silicon, oxygen, aluminum

  mantle - middle layer; rocks

  core - center; nickel and iron
• 1. crust (oceanic, continental)
  2. mohorovicic's discontinuity
  3. upper mantle
  4. lower mantle
  5. gutenberg discontinuity
  6. outer core
  7. lehmann's discontinuity
  8. inner core
• two parts of core are inner and outer
• inner core is the most difficult to study as it is inaccessible, information based on seismic information and computer models
• in 1936, it was inge lehmann who discovered that earth has a solid inner core
• the inner core has a radius of 1250 km, consists mainly of magnetic iron nickel alloy that is solid and cannot melt because of immense pressure, and it is 6000 celsius, as hot as a sun's surface
• the outer core is made out of iron and nickel, 2300 km thick, is 4000 to 5000 celsius, and has a molten metallic core whose magnetic field is linked to earth's rotation
• the boundary between outer and inner core is the lehmann discontinuity
• the two parts of mantle are lower and upper
• mantle is the largest part of earth and is made up of magma (molten rocks)
• magma circulates in currents, determined by cooling and sinking of heavier minerals, heating and rising of lighter minerals
• the lower mantle is hot and exhibits "plasticity", is soft/magma, has higher pressure and therefore occurs a formation of different minerals from upper layer, 2240 km thick, covers the asthenosphere
• gutenberg discontinuity is the boundary between lower mantle and outer core
• asthenosphere is a layer that lies after lithosphere, covers most of upper mantle, whose name was given by joseph barrel in 1914, and plays a critical role in plate movement
• lithosphere is located on the upper most mantle and crust
• the upper mantle covers the lithosphere, is rigid and solid, covers the moho boundary, and is 660 km thick
• mohorovicic discontinuity was discovered by andrija mohorovicic in 1904, this seperates the upper mantle and crust
• two parts of crusts are continental and oceanic crust
• oceanic crust is dark colored, basaltic, more dense, thinner, 50 km thick
• continental crust is light colored, granitic, less dense, course-textured, thick layer, 40 to 70 km thick