Transcript Earth`s interior

Inside the Earth
mysterious and inaccessible
Sources of Information
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Earthquakes
Magnetism
Gravity
Some rocks
Meteorites
Seismic Waves
• Surface waves
– Rayleigh waves: up and down component
– Love waves: side-to side component
• Body waves
– P-waves: compressive
– S-waves: shear
Wave Transmission
• Different speeds in different media
– Faster with high elasticity
– Slower with high density
• Reflection occurs at boundaries
• Direction can change with speed
Wave Refraction
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Direction
changes to
keep wave
front
continuous
Source: University of Southampton, Institute for Sound and Vibration Research
Refraction Example
u = 1/2
u = 3/4
u=1
Findings
• Speed increases with depth
• Definite layers
• Liquid outer core
Magnetism
• Earth has a magnetic field
• Interior too hot to be solid iron
• So: electric currents in liquid metal core
Gravity
• Earth has high density
• Gravity increases with depth in mines
• So: interior must be denser than exterior
Rocks
• Kimberlite pipes (all ancient)
– Deep origin
– Ultramafic composition
• Uplifted slabs
– Ultramafic composition
• So: mantle is ultramafic, largely olivine
Meteorites
• Types: stony, stony/iron, iron/nickel
• Protoplanetary solar system bodies
differentiated, then collided and
fragmented
• So: earth probably contains similar zones
Conclusions
• Inner core: Dense solid. High pressure
and temperature. Fe/Ni/S.
• Outer core: Liquid Fe/Ni/S.
• Mantle: Several layers. Plastic solid. Mafic
minerals (Fe and Mg silicates).
• Crust: Thin (5–75 km) low-density solid.