Exploring the inner and outer shells of earth

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Exploring the inner and outer shells of earth
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Earth consists of a series of concentric layers
or spheres which differ in chemistry and physical
properties.
Chemical Layers
Physical Layers
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Physical state is determined by the combined
effects of pressure and temperature.

• Increasing pressure raises the melting point of a
  material.
• Increasing temperature provides additional energy
  to the atoms and molecules of matter allowing
  them to move farther apart, eventually causing
  the material to melt.
• Both pressure and temperature increase toward the
  center of the Earth, but at variable rates.

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How do we learn about the inner structure of the
planet?
Seismic waves
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Seismology is the study of elastic waves that
travel through the earth Two main wave types
Compression waves (P-waves) travel by squeezing
and expanding medium they travel through. They
can travel through both solids and liquids (e.g.,
sound waves).
Shear waves (S-waves) travel by shearing
medium they pass through. S-waves can travel
only through solids since particles need to be
bonded to each other to propagate wave (similar
to a bull whip)
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Earthquake are an incredible source of seismic
waves

• Seismic waves travel along there quickest route,
  generally through, the planetary interior to the
  seismic stations, changing speed every time
  material properties change.

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Reconstructing the internal structure of the
planet
solid

• Crust upper mantle large increases in seismic
  velocities and density

solid, more dense

• Mantle Gradual velocity and density increase

Liquid Iron

• Outer core dramatic density increase and no
  S-waves

• Inner core Jump in density and P-wave velocity,
  S-waves return

solid Iron
Other planets?
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Earthquakes produce waves in the ocean
NOAA-GlobalOceanWave.mov
NOAA-IndianOceanWave.mov
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Earthquakes produce waves in the ocean
Sea level RISE FALL
Courtesy K. Satake, unpublished
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World Seismicity

• (1898-2003)

Mw 6.0
Mw 7.7
Many large earthquakes occur along subduction
zones
Most Great earthquakes are subduction
mega-thrust events
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Major Research Programs in Geophysics
http//www.earthscope.org/
http//www.margins.wustl.edu/
http//www.neptune.washington.edu/
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The Physiography of the North Atlantic Ocean Floor
http//topex.ucsd.edu
continental margins
deep ocean basins
midoceanic ridges
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• Continental margins are the submerged edges of
  the continents and consist of massive wedges of
  sediment eroded from the land and deposited along
  the continental edge. The continental margin can
  be divided into three parts the Continental
  shelf, the Continental slope, and the Continental
  rise.

Continental Margin
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• Deep Ocean Province is between the continental
  margins and the midoceanic ridge and includes a
  variety of features from mountainous to flat
  plains Abyssal plains, Abyssal hills, Seamounts,
  and Deep sea trenches.

Deep Ocean Basin
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• Midoceanic Ridge Province consists of a
  continuous submarine mountain range that covers
  about one third of the ocean floor and extends
  for about 60,000 km around the Earth.

Midocean Ridge
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WHY DO LAND AND OCEAN EXIST?
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Continents and ocean basins differ in
composition, elevation and physiographic features.
Geologic Differences between Continents and Ocean
Basins
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• Elevation of Earths surface displays a bimodal
  distribution with about 29 above sea level and
  much of the remainder at a depth of 4 to 5
  kilometers below sea level.
• Continental crust is mainly composed of granite,
  a light colored, lower density (2.7 gm/cm3)
  igneous rock rich in aluminum, silicon and
  oxygen.
• Oceanic crust is composed of basalt, a dark
  colored, higher density (2.9 gm/cm3) volcanic
  rock rich in silicon, oxygen and magnesium.

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Geologic Differences between Continents and Ocean
Basins
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WHY DO LAND AND OCEAN EXIST?
OCEANIC CRUST THIN AND DENSER CONTINENTAL CRUST
THICK AND LITHER
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100 cm3 39 g
A
10 cm3 12 g
B
WATER
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100 cm3 39 g
A
WATER
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Apositively buoyant
100 cm3 39 g
Bnegatively buoyant
WATER
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100 m3 39 kg
A
10 m3 12 kg
B
WATER
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Isostasy refers to the balance of an object
floating upon a fluid medium. Height of the
mass above and below the surface of the medium is
controlled by the thickness of the mass and its
density (similar to ice floating in water).
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• Continents are thick (30 to 40 km), have low
  density and rise high above the supporting mantle
  rocks.
• Sea floor is thin (4 to 10 km), has greater
  density and does not rise as high above the
  mantle.

Oceanic Crust Versus Continental Crust
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Three spheres surround the rocky portion of the
Earth.

• Hydrosphere includes all of the free water of
  the Earth contained in the ocean, lakes, rivers,
  snow, ice, water vapor and groundwater.
• Atmosphere is the gaseous envelope that surrounds
  the Earth and is mainly a mixture of nitrogen and
  oxygen.
• Biosphere refers to all living and non-living
  organic matter.

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End of lecture
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Exploring the inner and outer shells of earth
NOAA-GlobalOceanWave.mov
NOAA-IndianOceanWave.mov
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Exploring the inner outer shells of earth
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(No Transcript)
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WHY DO WE CARE ABOUT THE GEOMORPHOLOGY OF THE
OCEAN FLOOR? (in the context of Oceanography)