Geophysics/Tectonics Brief Review of the Universe

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Geophysics/Tectonics Brief Review of the
Universe

• GLY 325

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Anthropic Principle
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The Multiverse
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Geologic Time
History of the Earth (the short version)

• (1) Beginning of our Universe with the Big
• Bang 12 billion years ago (12 Ba).
• (2) 12 Ba to 7 Ba -- Galaxies, Stars, Planets
• form and are destroyed.
• (3) 7 Ba -- A particular Red Giant star
• catastrophically exploded (supernova).
• (4) 4.6 Ba -- The remnants of the particular
• supernova in (3) forms into our solar
• system including EARTH.

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Geologic Time
Open Universe Closed Universe
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Compositionof the Universe
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Geologic Time
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Geologic Time
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History of the Earth (the short version)

• Step 1 Accretion of cm sized particles
• Step 2 Physical Collision on km scale
• Step 3 Gravitational accretion on 10-100 km
  scale
• Step 4 Molten protoplanet from the heat of
  accretion

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History of the Earth (the short version)

• Final step is differentiation of the earth
• gt Light objects float heavy objects sink.
  Thus, Iron-Nickel Core and oxygen-silicon Crust
• Segregation of the Earth by composition.

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History of the Earth (the short version)

• To reiterate
• (1) Original Protoearth was molten
• (2) Dense material (molten nickel and iron)
  flowed to the center
• (3) Lighter material (molten silicon) flows to
  the top
• (4) Earth cools and solidifies into basic core,
  mantle and crust structure
• gt During cooling, the earth has a lot of
  trapped gasses in its interior.

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History of the Earth (the short version)

• Outgassing --gt Early Formation of the Earth's
  Atmosphere
• Present day composition of volcano effluents
• Water Vapor --gt 60
• Carbon Dioxide --gt 24
• Sulfur --gt 13
• Nitrogen --gt 5.7
• Argon --gt 0.3
• Chlorine --gt 0.1

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History of the Earth (the short version)

• It is likely that there was NOT enough water
  released via outgassing to account for the
  present day oceans
• Most of the water was likely delivered to the
  earth after it formed via collisions with left
  over planetisimals and cometisimals.

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History of the Earth (the short version)

• On Mars it was too cold and water vapor condensed
  (i.e, came out of the atmosphere). Hence the
  atmosphere is all Carbon Dioxide
• On Venus it was too hot for water vapor to
  condense (no liquid water). So weathering could
  not progress and CO2 could not disolve in liquid
  water. Hence the atmosphere remained rich in
  Carbon Dioxide
• On Earth it was just right. The carbon dioxide
  content of the earth's atmosphere is now all
  locked up in rocks and oceans.

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History of the Earth (the short version)

• There are two keys to the evolution of planetary
  atmospheres
• Fate of the water vapor (gaseous, liquid, solid)
• Fate of the Carbon Dioxide (stays in atmosphere
  vs. dissolves in liquid water or locked in rocks)

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History of the Earth (the short version)

• After condensation of water vapor, the earth's
  oceans were produced, thus sweeping out the
  carbon dioxide and locking it up into rocks.
• Currently, our atmosphere is 72 nitrogen and 28
  oxygen (everything else like H2 and CO2 exists
  only in trace amounts).
• So where did the oxygen come from...?

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Introduction to Whole Earth Geophysics and
Tectonics

• Geology 325

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Geophysics

• The application of physical principles to the
  study of the earth. Includes branches of
  seismology, geothermometry, hydrology, physical
  oceanography, meteorology, gravity and geodesy,
  terrestrial magnetometry, tectonophysics,
  engineering and exploration geophysics,
  geochronology, and geocosmogony.
• The study of the earth by quantitative physical
  methods, especially by seismic reflection and
  refraction, gravity, magnetic, electromagnetic,
  and radioactivity methods.

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Geophysics

• Based on measuring five Earth properties
• Density (measured as the local force of gravity).
• Magnetization (measured as the local magnetic
  force).
• Acoustical response (measured in terms of
  voltages derived from geophones or hydrophones).
• Electrochemical (measured by various electrodes,
  Geiger counters, etc).
• Heat flow (crustal thickness)

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Potential Field Methods

• The measured strength and direction depends on
  your position of observation within the field.
• The measured strength of the field generally
  decreases with increased distance.
• Gravity and magnetics are potential field
  methods.

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Gravity Methods

• Measures localized changes in the acceleration of
  gravity as a result of changes in density.
• Affected by the thickening or thinning of the
  crust.
• Affected by the presence or absence of mass
  (mountains or deep valleys).

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Gravity Methods (for our purposes)

• Used to measure crustal thickness, obtain
  information on deep crustal structure, and obtain
  information on transitional crustal zones
  (continental margins).

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Magnetic Methods

• Measures localized changes in the direction and
  strength of the magnetic field as a result of
  changes in magnetic susceptibility (?) and
  remnant magnetism (Jrem).

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Magnetic Methods (for our purposes)

• Identification of magnetic reversal stripes on
  the sea floor was one of the key components of
  recognizing plate tectonics.
• Paleomagnetism and polar wander curves were
  critical in determining the locations of
  continental plates during geologic time.
• Paleomagnetism were critical in determining the
  presence of exotic terranes.
• Used to map the transition zone between
  continental and oceanic crust.
• Used to map deep crustal structure.

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Seismic Methods

• Measures the rigidity or elastic properties by
  examining the velocity of seismic waves through
  the Earth.
• Natural sources of seismic waves are earthquakes.
• An example of man made or induced sources are
  explosions or striking a surface with a hammer.

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Seismic Methods

• Essential for determining the composition, phase,
  and depth boundaries of the Earths interior.
• Essential data for developing the plate tectonic
  paradigm.

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Heat Flow Methods

• Measures the thermal conductivity (k) of the
  rocks and their geothermal gradient to calculate
  heat flow (q).

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Heat Flow Methods

• Essential for understanding plate motion,
  rifting, and hot spots.