8th Grade Science

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8th Grade Science

• Unit 8 Changes Over Time
• Lesson 2 Changes in the Rocks
• Vocabulary of Instruction

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1. Landform

• Landforms are natural features of the landscape.
• They are natural physical features of the earth's
  surface.
• Examples of Landforms are valleys, plateaus,
  mountains, plains, hills, loess, and glaciers.

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1-A. Landform - Valley

• A valley is a hollow or surface depression of the
  earth surrounded by hills or mountains.
• It is a natural trough in the earth's surface,
  that slopes down to a stream, lake, or the ocean,
  formed by water and/or ice erosion.

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1-B. Landform - Plateau

• A plateau is a large highland area of fairly
  level land separated from surrounding land by
  steep slopes.
• Some plateaus, like the plateau of Tibet, lie
  between mountain ranges. Others are higher than
  surrounding land.
• Plateaus are widespread, and together with
  enclosed basins they cover about 45 percent of
  the Earth's land surface.

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1-C. Landform - Mountains

• Mountains are formed by volcanism, erosion, and
  disturbances or uplift in the earth's crust.
• Most geologists believe that the majority of
  mountains are formed by geological forces such as
  heat and pressure producing changes and movements
  under the earth's crust.

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1-D. Landform - Plains

• Plains are broad, nearly level stretches of land
  that have no great changes in elevation.
• Plains are generally lower than the land around
  them they may be found along a coast or inland.
• Coastal plains generally rise from sea level
  until they meet higher landforms such as
  mountains or plateaus.
• Inland plains may be found at high altitudes.

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1-E. Landform - Hills

• Hills are elevations of the earth's surface that
  have distinct summits, but are lower in elevation
  than mountains.
• Hills may be formed by a buildup of rock debris
  or sand deposited by glaciers and wind.
• Hills may be created by faults. Faults are a
  slight crack in the earth which can cause
  earthquakes.
• Hills are formed when these faults go slightly
  upward.

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1-F. Landform - Loess

• Loess is a geologically recent deposit of silt or
  material which is usually yellowish or brown in
  color and consisting of tiny mineral particles
  brought by wind to the places where they now lie.
  
• It is a product of past glacial activity in an
  area.
• It is a sedimentary deposit of mineral particles
  which are finer than sand but coarser than dust
  or clay, deposited by the wind.
• Loess is a type of silt which forms fertile
  topsoil in some parts of the world.
• Loess deposits are usually a few meters thick.

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1-G. Landform - Glacier

• A glacier is a huge mass of ice that flows slowly
  over land.
• They form in the cold polar regions and in high
  mountains.
• The low temperatures in these places enable large
  amounts of snow to build up and turn into ice.
• Most glaciers range in thickness from about 91 to
  3,000 meters.
• Glaciers are formed when more snow falls during
  the winter than melts and evaporates in summer.

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2. Contour Line (Isoline)

• A contour line is a line on a map that connects
  points or places of equal elevation.
• The bottom part of the diagram shows some contour
  lines with a straight line running through the
  location of the maximum value.
• The curve at the top represents the values along
  that straight line.

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3. Topographic Map (Contour Map)

• Is a map that shows the change in elevation of
  the Earths surface using contour lines.
• It shows shapes and features of the Earth surface
  such as roads, lakes, and cities.
• Traditional definitions require a topographic map
  to show both natural and man-made features.

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4. Rock Cycle

• The Rock cycle describes the dynamic transitions
  through geologic time among the three main rock
  types sedimentary, metamorphic, and igneous.
• As the diagram to the right illustrates, each
  type of rock is altered, changed, or destroyed
  when it is subject to factors such as heat,
  pressure, cooling, and erosion.

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4-A. Rock Cycle - Diagram

• The rock cycle starts at is the magma chamber.
  The magma comes out of the volcano and cools into
  igneous rocks.
• Next, the igneous rocks erode and turn into
  sediments.
• The sediments go through years of pressure and
  cementation which turns the sediments into
  sedimentary rock layers.
• Once again the sedimentary rocks go through heat
  and pressure and turn into metamorphic rocks.
• Then the new metamorphic rocks go through heat
  and turn into magma.

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4-B. Rock Cycle Diagram Cont

• Also, igneous rocks can go through heat and
  pressure and become metamorphic rocks.
• Metamorphic and sedimentary rocks can become
  sediments.
• That is how the rock cycle works.

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4-C. Rock Cycle Diagram Cont

• Another representation of the rock cycle
  processes is shown on the picture to the left.

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4-D. Rock CycleThree Types of Rocks

• 1. Igneous Rock
• Lava flowing from a volcano in Hawaii forms
  igneous rocks.

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4-D. Rock CycleThree Types of Rocks

• 2. Metamorphic rock
• In Arizona metamorphic rocks show formerly flat
  sedimentary layers squeezed into new shapes.

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4-D. Rock CycleThree Types of Rocks

• 3. Sedimentary Rock.
• Metamorphic Rocks in Hawaii have been broken into
  sediments and have accumulated on this beach,
  where they might form a sedimentary rock through
  pressure and cementation.

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4-D. Rock CycleThree Types of Rocks

• Sedimentary and metamorphic rocks in Arizona were
  broken into sediments and carried away, leaving
  the Grand Canyon behind, one of the wonders of
  the world.

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