Pgs 11-4 to 11-29

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Chapter 11

• Pgs 11-4 to 11-29

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Layers of the Earthpgs 11-4 to 11-6

• The current theory is that the Earths interior
  consists of multiple layers
• Inner core
• Outer core
• Mantle
• Crust

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The inner core

• The center of the Earth
• Made up primarily of iron, nickel, other heavy
  elements
• It is theorized to be solid due to enormous
  pressure

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The Outer Core

• Made of the same elements as the inner core, but
  with less pressure, it is theorized to be liquid

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The Mantle

• Contains mostly silicon and oxygen
• makes up nearly 80 percent of the Earth's total
  volume.
• Consists of the upper and lower mantle
• The upper mantle itself is made of 2 layers
• Asthenosphere
• Lithosphere

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Lithosphere and Asthenosphere

• Lithosphere
• includes the uppermost, rigid part of the upper
  mantle and the crust.
• Asthenosphere
• Solid but flows slowly over time
• Hotter, less dense material (magma) rises towards
  the surface where it can eventually flow from a
  volcano or other opening. At this point the
  molten rock is lava.
• The flowing asthenosphere carries the lithosphere
  of the Earth, including the continents, on its
  back.

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The Crust

• composed mainly of oxygen, silicon, magnesium,
  and iron
• Varies in thickness and is the outer layer of the
  lithosphere

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11-7 to 11-8 Isostatic Equilibrium

• Even before the plate tectonics theory emerged,
  scientists believed that the crust floated on the
  denser mantle below
• Still believed today
• Continental crust (crust under the continents)
• Ocean crust (crust under the ocean basins)

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• Oceanic crust is thinner and denser than
  continental crust
• Because the continental crust is made of granite
  and the oceanic crust is made of basalt rock

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Interaction of Oceanic Crust and Continental Crust

• With the crust resting on the mantle, there must
  be a balance between the weight of the crust and
  the upward force of buoyancy
• called isostatic equilibrium
• As material adds to the oceanic crust from
  sedimentation, glaciers and volcanic activity or
  from the continental crust from erosion, this
  balance becomes disrupted. This is one theorized
  cause of earthquakes.
• To restore equilibrium, landmasses will sink or
  rise slightly along a weak area called a fault.

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• The accepted theory of plate tectonicssuggests
  that the continents move inhorizontal directions
  and that earthquakesalso result from that
  movement.

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The Theory of Continental Drift11-10 to 11-13

• Proposed by Alfred Wegener
• All earths continents had been a single
  continent that he called Pangaea

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CONTINENTAL DRIFTPangaea broke up with part of
the continent drifting north and part south. 1)
The northern part split to form the North
Atlantic Ocean 208-146 million years ago (mya).
2) The South Atlantic and Indian oceans began to
form 146-65 mya. 3) The continents continue to
drift. Today the oceans are still changing shape
the Atlantic Ocean gets wider by a few inches
each year.
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• Surrounding Pangaea was a single large ocean he
  called Panthalassa
• The theory that all of the continents were once a
  single landmass that drifted apart (and are still
  doing so) is called the theory of continental
  drift

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Evidence for Continental Driftpgs 11-10 through
11-13

• Appeared that the continents fit together like
  jigsaw puzzle pieces
• Fossils found in different locations
• Distribution of coal
• Glacial rock deposits
• Limestone deposits
• Salt deposits

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Criticism of Continental Drift

• Wegener was a meteorologist, not a geologist
• Could not give an explanation of how the
  continents could drift
• Jigsaw puzzle had gaps

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Seafloor Spreading pgs 11-14 to 11-18

• New technology- sonar
• Came about at the same time as the continental
  drift theory and partly in response to the
  Titanic disaster

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The German Meteor mapped the contours and depths
of the South Atlantic in 1925 using sonar

• The ability to map the seafloor in greater detail
  revealed important new features
• Mid-ocean ridges are enormous mountain ridges on
  the bottom of the ocean.
• Rift valleys are deep valleysrunning through the
  center ofmid-ocean ridges such asthe Atlantic
  Ridge.
• Trenches are deep ravinesin the seafloor.

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• The idea that the seafloor is in a constant state
  of creation and destruction is called seafloor
  spreading- an explanation proposed by Harry Hess
  and Robert Dietz.

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• New crust emerges from the rift valley in a
  mid-ocean ridge
• Magma from the asthenosphere pushes up through
  the rift and solidifies into new crust
• As more magma pushes up from below, it pushes new
  crust away on each side of the ridge
• New seafloor near the ridge continuously pushes
  old seafloor away from the ridge

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Evidence for Seafloor Spreading11-17 to 11-18

• Ocean-bottom sediment samples
• Glomar Challenger- coring

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• Radiometric dating
• Used to determine the age of rocks
• Seafloor rock- significantly younger than rock in
  the center of the continents (theory states that
  seafloor rock subsides and continental rock
  doesnt).

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• Magnetometer data
• measures the polar orientation and intensity of
  magnetism of minerals
• Scientists towed magnetometers around the
  seafloor beginning in 1950
• discovered that the seafloor on either side of
  the mid-ocean ridges roughly mirrors each others
  polar orientation

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Divergent, Convergent, Transform Plate
Boundaries 11-22 to 11-25

• The theory of plate tectonics unites the theories
  of continental drift and seafloor spreading.
• Earths lithosphere consists of more than a dozen
  separate plates
• rigid and float on the asthenosphere.

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Divergent Boundaries

• At a spreading, or divergent boundary, two plates
  are moving apart
• The crust pulls apart and forms valleys.
• Magma flows up through the rift valleys creating
  new crust and widening the seafloor.
• Mid-ocean ridges and rift valleys mark divergent
  boundaries.

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Hot Spots

• Stationary plume of magma under a moving plate
• Creates volcanic islands in the middle of plates
• EX Hawaiian Islands and the Emperor Seamount
  Chain

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Convergent Boundaries

• At a colliding or convergent boundary, two plates
  push together
• also called destructive boundaries because
  movements along these destroy crust
• Subduction zones (convergent boundary).
• A trench forms as a more dense oceanic plate
  moves under a less dense continental plate. As
  subduction occurs, some of the material from the
  melting oceanic plate rises upward to form
  volcanoes on the continent.
• Mountain formation at continental plate
  collision.

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Transform Boundaries

• At a transform boundary or fault, two plates
  slide past each other.
• Earthquakes result as rocks move when the plates
  slide next to each other.
• Ex Californias San Andreas Fault

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Ocean Floor Topography Vocabulary

• Continental Shelf the part of the continent that
  is under water. It is the biologically richest
  part of the ocean. At times of low sea level the
  shelves were exposed.
• Continental Slope the edge of the continent.
  Extends downward to the deep-sea floor.
• Continental Rise a gentle slope or a rise on the
  bottom of the ocean that is due to the sediments
  being carried down the slope. The sediment is
  carried downward by the turbidity current.

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• Seamount underwater volcanoes due to hotspots
  and magma. Formed when magma below is pushed
  upward and cooled and solidified.
• Mid-Ocean Ridge the cracks in the bottom of the
  ocean where the plates meet. Is called an
  underwater mountain range.
• Rift Valley a valley between 2 plates. Caused
  when the 2 plates are pushed apart and the
  sea-bottom collapses forming a valley between the
  2 ridges.
• Abyssal Plain the almost perfectly flat area of
  the ocean. Flat due to deposits of sediments and
  erosion. Called the ocean desert because few life
  forms exist here.

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• Guyot a flat-topped underwater mountain. It is
  flat at the top due to erosion.
• Trench a narrow depression on the sea floor.
  Caused when 2 plates collide and one plate is
  pushed under the other one and pulls the sea
  bottom with it. The deepest trench is the
  Marianas trench with a depth of 11,022 meters, or
  almost 7 miles.
• SONAR uses echolocation or sound waves to see
  the seafloor and make an accurate map of it.

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SONAR is used to make accurate maps of the ocean
floor.
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Sediments 12-10 to 12-12

• Lithogenous sediments come from the land
• Mainly result from erosion by water, wind, and
  ice carrying rock and mineral particles into the
  sea.
• Other lithogenous sediments enter the sea from
  landslides and volcanic eruptions
• Make up majority of sediments found near
  continents and islands
• Includes sand and clay

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• Biogenous sediments originate from organisms
• Particles in the sediment come from shells and
  hard skeletons
• Cover the largest area of sea floor.
• The majority of biogenous sediment comes from
  planktonic organisms that obtain siliceous and
  calcareous compounds from seawater.
• Under the right conditions, organic molecules in
  the sediment form crude oil (petroleum) and
  natural gas

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• Hydrogenous sediment results from chemical
  reactions within seawater
• Less than 1 of the seafloor sediments
• Form slowly

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• Cosmogenous sediments come from outer space
• Made up of small particles the size of sand or
  smaller called cosmic dust.
• Some thought to result from collisions between
  objects in space
• Meteors large, fast-moving objects that enter
  the atmosphere
• Meteorite a meteor that strikes the ground
• Least abundant of the sediments- a few parts per
  million of marine sediment per year