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: $50 \text{ km} \text{ to } 100 \text{ km}.$