Earth's Interior: Study Notes

Crust

  • Earth's crust thickness: from the surface to about 32 \text{ km} to 72 \text{ km}.
  • Subtypes:
    • Continental crust:
    • Composition: \text{Si}, \text{O}, \text{Al}, \text{Ca}, \text{Na}, \text{K}
    • Rock type: granite rocks
    • Thickness: 35 \text{ km} \text{ to } 40 \text{ km}
    • Oceanic crust:
    • Thickness: 7 \text{ to } 10 \text{ km}
    • Average thickness: around 8 \text{ km}
    • Rock type: basalt rocks
    • Composition: basalt rocks
    • Density note: Oceanic crust is described as less dense rocks (basalt) in the notes, and it is stated to be heavier than the continental crust.
  • General crust composition (elemental overview):
    • Oxygen: 46.60 \%
    • Silicon: 27.72 \%
    • Aluminum: 8.13 \%
    • Iron: 5.00 \%
    • Calcium: 3.63 \%
    • Sodium: 2.83 \%
    • Potassium: 2.59 \%
    • Magnesium: 2.09 \%
    • Titanium: 0.40 \%
    • Hydrogen: 0.14 \%

Mantle

  • Overall mantle extent: extends to about 2900 \text{ km} from the Earth’s surface.
  • Volume and mass:
    • 80\% of the Earth’s total volume
    • 68\% of the total mass
  • Composition: silicate rocks; solid.
  • P-waves and S-waves can pass through the mantle.
  • Mantle structure:
    • Lithosphere: thickness 50 \text{ km} \text{ to } 100 \text{ km}
    • Upper Asthenosphere: thickness 150 \text{ km}
    • Asthenosphere: temperature 300 \circ\text{C} \text{ to } 800 \circ\text{C}; made of hot molten material.
  • Mantle rocks:
    • Volcanoes rocks are formed in the mantle.
    • Mantle composition: Silicon, Oxygen, Iron, Magnesium.
    • Lower mantle contains more iron compared to the upper mantle.
  • Density and flow:
    • The lower mantle is denser than the upper portion.
    • Temperature and pressure increase with depth, allowing solid rock to flow slowly under high temperature/pressure conditions.

Core and boundaries

  • Mohorovičić Discontinuity (MOHO):
    • Boundary between the crust and the upper part of the mantle.
    • The outer shell formed is called the lithosphere.
    • Thickness: 50 \text{ km} \text{ to } 100 \text{ km}.
    • Named after Andrija Mohorovičić.
  • Gutenberg Boundary:
    • Boundary between the mantle and the outer core.
    • Named after Beno Gutenberg.

Outer Core

  • Position: located at \approx 2900 \text{ km} below the Earth’s surface.
  • Thickness: 2250 \text{ km}.
  • Composition: iron and nickel.
  • Temperature: 2000 \circ\text{C}.
  • State: liquid.

Inner Core

  • Composition: solid iron and nickel.
  • Radius: 1300 \text{ km}.
  • Temperature: 5000 \circ\text{C}.
  • State: solid core.

Lithosphere and related concepts

  • Lithosphere:
    • Outermost rigid shell including the crust and the uppermost mantle.
    • Associated with MOHO as its boundary layer.

Connections and implications

  • Seismology:
    • P-waves and S-waves behavior through mantle and core layers helps infer the presence of liquid outer core (as per notes on wave transmission in the mantle region).
  • Plate tectonics and volcanism:
    • Mantle convection and the presence of molten material in the asthenosphere drive plate motions and volcanic activity.
  • Real-world relevance:
    • Understanding layer properties explains earthquakes, volcanic activity, and the planet's magnetic field generated by the molten, convecting outer core.

Quick reference of key values

  • Crust thickness (thinnest to thickest): 7 \text{ km} \leq \text{Oceanic crust} \leq 10 \text{ km}; Continental crust 35 \text{ km} \leq \text{Continental crust} \leq 40 \text{ km}; overall crustal thickness from 32 \text{ km} to 72 \text{ km} (in mountains).
  • Mantle: 2900 \text{ km} thick from surface; 80\% of volume; 68\% of mass.
  • Asthenosphere temperature: 300 \circ\text{C} \text{ to } 800 \circ\text{C}.
  • Outer Core: 2250 \text{ km} thick, at 2000 \circ\text{C}, composed of Fe and Ni.
  • Inner Core: 1300 \text{ km} radius, at 5000 \circ\text{C}, solid Fe-Ni.
  • Moho thickness: 50 \text{ km} \text{ to } 100 \text{ km}.