Earth Structure

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Earth Structure
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• Mexico quake-- magnitude at 7.0, and epicenter
  was in the western Pacific state of Michoacan.
  Its depth was about 40 miles
• Indonesia-- earthquake off coast of Indonesia
  Wednesday, April 11 with magnitude of 8.6,
  sparking tsunami warnings

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Lithosphere

• Consists of continental, oceanic and upper part
  of mantle

• Continents composed of granite-type rock, quartz
  and feldspar minerals, density2.8g/cm3

• Oceanic crust formed of basalt basalt rich in
  iron/magnesium minerals, density3.0 g/cm3

• Lithosphere is rigid layer of crust and mantle
  overlying partially-molten asthenosphere

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Why Continents Higher and Ocean Floor Lower

• IsostacyPrinciple that less dense continental
  crust sits higher on the mantle while denser
  oceanic crust sits lower
• http//www.youtube.com/watch?vG9rN7qhUQZgfeature
  player_detailpage

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Continental Drift Evidence

• Researchers noted geographic fit of continents
• e.g. Africa and S. America
• Atlantic formed by separation of Africa from S.
  America

• Seuss, 1885, proposed super continent by studying
  fossils, rocks, mountains

• Wegener and Taylor, early 1900s, proposed
  continental drift and Pangaea

• Evidence supporting the idea that the continents
  had drifted.

• Geographic fit of continents
• Fossils
• Mountains
• Glaciation

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Continental Drift Geographic Fit

• Continents seem to fit together like pieces of a
  puzzle

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Continental DriftFossils

• Similar distribution of fossils such as the
  Mesosaurus

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Continental DriftMountains

• Mountain ranges match across oceans

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Continental DriftGlaciation

• Glacial ages and climate evidence

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Objectionsto theContinental Drift Model

• Wegener did not provide a plausible mechanism to
  explain how the continents could have drifted.

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Seafloor Spreading

• Continental drift reexamined in 1960s with new
  information

• New theory developed Seafloor spreading

• Supporting evidence for seafloor spreading

• World seismicity

• Volcanism

• Age of seafloor

• Paleomagnetism

• Heat flow

• Theory combining continental drift and seafloor
  spreading termed Plate Tectonics

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Seafloor Spreading

• New sea floor created at the mid-ocean ridge and
  destroyed in deep ocean trenches

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Evidence for Seafloor SpreadingWorld Seismicity

• Earthquake distribution matches plate boundaries

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Evidence for Seafloor SpreadingVolcanism

• Volcanoes match some plate boundaries some are
  hot spots

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Evidence for Seafloor SpreadingAge of Seafloor

• Youngest sea floor is at mid-ocean ridge
• Oldest sea floor away from mid-ocean ridge

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Evidence for Seafloor SpreadingPaleomagnetism

• Earth has a magnetic field - Probably caused by
  rotation of solid inner core in liquid outer core
  (both mostly Fe)

• When rocks cool at the Earths surface, they
  record Earths magnetic field (normal or reverse
  polarity)

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Evidence for Seafloor SpreadingPaleomagnetism

• Paleomagnetic studies indicate alternating
  stripes of normal and reverse polarity at the
  mid-ocean ridge.

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Seafloor SpreadingHeat Flow

• In 1960, convection currents were proposed as
  driving force to move continents

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Theory of Plate Tectonics

• John Tuzo Wilson combined ideas of continental
  drift and seafloor spreading into Plate
  Tectonics

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Principles of Plate Tectonics

• Earths outermost layer composed of thin rigid
  plates moving horizontally

• Plates interact with each other along their edges
  (plate boundaries)

• Plate boundaries have a high degree of tectonic
  activity
• mountain building
• earthquakes
• volcanoes

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Plate BoundariesThree types
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Plate BoundariesDivergent

• Plates move away from each other
• New crust is being formed

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Divergent Plate BoundariesExamples
Mid-Atlantic Ocean Ridge
East African Rift
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Plate BoundariesConvergent
Three Types

• Ocean-continent

• Ocean-ocean

• Continent-continent

• Plates are moving toward each other
• Crust is being destroyed

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Convergent Plate BoundariesExamples
Mount Fuji, Japan
Mount Lassen, California
Andes, South America
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Plate BoundariesTransform
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• Plates slide past one another

• Crust is neither created nor destroyed

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Transform Plate BoundariesExamples
Calexico, California
San Andreas Fault
Carrizo Plains, Central California