the earths layers and evidence

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  • layers of the earth + evidence
    • crust
      • the nature of the crust is well known from direct observation.
      • oceanic crust is very different from continental crust.
    • Moho discontinuity
      • a distinct and clear boundary marking a change of rock type and density.
      • the p and s waves velocity suddenly decreases
    • upper mantel
      • the upper mantel is solid
      • the main rock type is peridotite
      • the upper mantel consists of solid silicates, less dense  than the lower mantel
      • s waves can travel through the mantel
    • low velocity seismic  zone
      • 100-250km - 5% molten
    • the lower mantel
      • solid due to the increasing pressure, causing the rock to become more rigid and incompressible
      • the mantel is made out of the same silicate material as stony meteorites
      • s waves can travel trough the mantel
      • both p and s waves steadily increase velocity with depth
    • the Gutenberg discontinuity
      • a distinct and clear boundary marking  a change of mineral from metallic iron nickel to silicate material.
      • there is also a change in state between the liquid outer core and the solid lower mantel
      • the p wave velocity suddenly decreases and the s waves stop altogether
    • the outer core
      • the outer core is liquid and reduces rigidity
      • the pressure in the outer core is less than in the inner core, allowing liquid to exist
      • s waves do not travel through the outer core which shows that it must be a liquid
      • p waves slow down due to the rigidity
    • lithosphere
      • the crust and the region of the upper mantel above the asthenosphere is called the lithosphere
    • the Lehman discontinuity
      • a phase boundary of about 100km where the rock changes from liquid in the outer core through  liquid solid transition to all solid in the inner core
      • the p wave velocity increases at the boundary
    • inner core
      • the inner core is solid because o f the extreme pressure 3600000Ats, compared to 1 at the surface
      • the ion of the composition is iron-nickel
      • the dencity is more than 12gcm-3
      • p and s waves travel through the inner core
      • s waves are generated by p waves at the Lehman discontinuity
      • iron meteorites
      • the earth has a magnetic filed

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