EESA06H3 Chapter Notes - Chapter 4: The Crust, History Of Earth

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16 Apr 2011
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Chapter 4: The Earths Interior
Geophysicsapplication of physical laws and principles to a study of the Earth (includes study of
seismic waves and Earths magnetic field, gravity, and heat)
WHAT CAN WE LEARN FROM THE STUDY OF SEISMIC WAVES?
Seismic Reflectionreturn of some energy of seismic waves to the Earths surface after waves bounce
off a rock boundary
Seismic Refractionbending of seismic waves as they pass from one material to another (similar to how
light waves bend when passing through lenses of eyeglasses.
Diagram 4.3 pg. 107 (Station 1 and Station 2)
WHAT IS INSIDE THE EARTH?
Crust outer layer of rock, which forms thin skin on Earths surface
Mantlelies below crust, thick shell of rock that separates crust above from core below
Core central zone of Earth, probably metallic and source of Earths magnetic field
The Crust
Seismic waves travel faster in oceanic crust than in continental crust
Seismic P waves travel through oceanic crust at about 7 km/sec and through continental crust at
about 6 km/sec
Average thickness of oceanic crust is 7 km varying from 5-8 km. Avg. thickness of continental
crust 30-50 km varying from 10-70 km.
Felsicrocks high in feldspar, Siliconfor continental crust, Mafic rocks high in magnesium
and iron (ferric)for oceanic crust
Continental crust less dense the oceanic crust
Mohorovičić discontinuity (Moho)boundary separating crust from mantle beneath
The Mantle
Geoscientists interpret it to be made of solid rock
P waves travel at about 8 km/sec in upper mantle
Mantle different type of rock from oceanic or continental crust, hypothesis of geoscientists say it
is made up of Ultramafic rock
Ultramafic Rockdense igneous rock compose mainly of ferromagnesian minerals such as
olivine and pyroxene
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