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Topic Xii

• Earth Dynamic
• Crust

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I. Evidence of Crustal Movement

• A. Original Horizontality assumes that
  sedimentary rock is deposited in flat layers.
• What causes these layers to shift?

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B. Types of Crustal Activity

• 1. Faulting cracks within Earths crust.
• 2. Folding bending of rock layers
• 3. Tilting rock layers pushed on an angle.

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II. Earthquake the vibration or shaking of
earths crust caused by seismic waves.

• A. Types of Seismic Waves
• 1. Primary Waves P waves are compressional
  waves that travel fast through both liquids and
  solid rock.

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2. Secondary Waves S waves are shear waves
that travel slowly through solid rock only.
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III. Earthquake Location

• A. Focus the point below earths surface where
  the earthquake originates.
• B. Epicenter the point on Earths surface
  straight above the focus.

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C. Calculating Epicenter Distance requires the
difference in arrival times of P and S waves
to a seismic station.

• The further the seismic station is from the
  epicenter the greater the difference in arrival
  time between the two waves.

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D. Epicenter Location requires 3 seismic station
readings. Where all 3 intersect is the epicenter.
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E. Measuring Earthquake Strength

• 1. Mercalli Scale measures the earthquakes
  intensity based on the description of the damaged
  caused.
• larger number indicates greater damage.

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2. Richter Scale a magnitude scale used to
describe the amount of energy released by an
earthquake.

• a. Each step increase represents an increase of
  10 times the next lower number.
• Ex. A magnitude 7 is 10 times greater than a 6,
  but 100 times greater than a mag. 5.

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IV. Earths Layers Earth is divided into four
major zones crust, mantle, outer core and inner
core.

• A. Crust lithosphere outer most layer and
  relatively thin (10-65 kilometers).
• 1. Continental Crust
• thicker
• mostly granite
• low density 2.7 g/cm3

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2. Oceanic Crustthinmostly basaltmore
dense 3.0 g/cm3
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B. Mantle located below the crust. Separated
from the crust by the Moho interface.

• 1. Asthenosphere upper mantle flows like a
  thick plastic fluid.
• 2. Stiffer Mantle thicker and more solid.

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C. Outer Core made up of liquid iron.

• D. Inner Core made up of solid iron and nickel.
  
• 1. Meteorites are composed of similar material
  (Fe and Ni) as Earths inner core.

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2. Shadow Zone a dynamic band around Earth that
receives no P or S from an earthquake
epicenter.

• a. S waves are absorbed by the liquid outer
  core.
• b. P waves are refracted (bent) due to the
  different material densities of Earths layers.

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V. Continental Drift theory proposed by Alfred
Wegener stating that Earths crust is shifting.

• A. Wegeners Evidence
• 1. Continental coastlines fit like a jigsaw
  puzzle.
• 2. Similar rocks, minerals and fossils found on
  separate continents.
• 3. Tropical plant fossils found in Antarctica.

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VI. Plate Tectonics Theory states that Earths
crust is divided into large plates riding on the
asthenosphere.

• plates can consist of continental crust, oceanic
  crust or both.
• Ref. Table pg. 5
• Arrows indicate direction of movement.

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A. Mantle Convection Currents are believed to be
the driving force behind plate movement.

• 1. Hot, less dense magma rises at mid ocean
  ridges and pushes plates apart.

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B. Evidence of Plate Tectonics

• 1. Seafloor Spreading new ocean crust is formed
  by rising magma at mid-ocean ridges.
• the further from the ridge the older the rock!

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2. Magnetic Reversals Earths magnetic poles
reverse over time creating a pattern in newly
formed ocean crust.

• magnetic minerals in the new rock align
  themselves with Earths magnetic field.
• identical magnetic patterns are found on both
  sides of the ocean ridge.

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C. Plate Boundaries the interface between plates
where earthquakes and volcanoes occur.

• 1. Convergent Boundary two plates collide with
  each other.
• subduction occurs if dense ocean crust collides
  with continental crust, creating deep ocean
  trenches.

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2. Divergent Boundary where two plates are
moving apart. Occurs at mid-ocean ridges.
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3. Transform Boundary two plates slide past each
other. Ex. San Andreas fault
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4. Hot Spots plumes of hot magma from the mantle
producing volcanoes.

• as a plate moves over the hot spot, chains of
  volcanic mountains form. Ex. The Hawaiian
  islands.