8th Grade Science

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8th Grade Science

• Unit 8 Changes Over Time
• Lesson 3 Forces Behind Change
• Vocabulary of Instruction

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1. Asthenosphere

• Is the soft -plastic like- layer of the Earths
  mantle on which the lithospheric plates float and
  move around.

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2. Continental Drift

• The theory that all continents were once
  connected in a single large landmass that broke
  apart about 200 million years ago and drifted
  slowly to their current positions.
• German scientist Alfred Wegener was the first to
  come up with this theory.

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3. Convergent Boundary

• A plate boundary where two plates move towards
  each other and collide.
• The plate collisions that occur in these areas
  can produce earthquakes, volcanic activity, and
  crustal deformation.

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4. Divergent Boundary

• A plate boundary where two plates move away from
  each other, forming either mid-oceanic ridges or
  rift valleys.
• Divergent boundaries between oceanic plates form
  submarine mountain range such as the Mid-Atlantic
  Ridge volcanic activity in the form of fissure
  eruptions shallow earthquake activity creation
  of new seafloor and a widening ocean basin.

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5. Erosion

• Process in which surface materials (fragments of
  rocks and soil) are worn away and transported
  from one place to another by agents such as
  gravity, water, wind, and glaciers.

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6. Land Subsidence

• The sinking or subsiding of land surface as a
  result of geologic processes or human activities.

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7. Lithosphere

• Solid and rigid layer of Earth consisting of the
  crust and part of the upper mantle. It is about
  100 km thick.
• The lithosphere is brittle enough at some
  locations to fracture and produce earthquakes.

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8. Mid-Ocean Ridge

• Area where new ocean floor is formed when lava
  erupts through cracks in the Earths crust.
• It is a divergent plate boundary.

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9. Neap Tide

• A tide with the least difference between low and
  high tide that occurs when the Earth, moon and
  sun are arranged perpendicular to each other
  (pull at right angles to the Earth).
• Neap tide comes twice a month, in the first and
  third quarters of the moon.

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10. Pangaea

• The large ancient landmass that was composed of
  the entire continents joined together that broke
  apart 225 million years ago and gave rise to
  todays continents.

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11. Plate Tectonics

• The theory that Earths crust and upper mantle
  are broken into plates that floats and move
  around on a plastic like layer of the mantle.

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12. Sea-Floor Spreading

• Hesss theory that new seafloor (oceanic crust)
  is formed when magna is forced upward toward the
  surface at a mid-ocean ridge.

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13. Spring Tide

• A tide with the greatest difference between high
  and low tide that occurs when the Earth, moon and
  sun are arranged in a straight line, during the
  new and full moon phases.
• Spring tides happen twice a month.

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14. Transform Boundary

• A plate boundary where two tectonic plates slide,
  grind, and past each other in opposite directions
  along a transform fault. (also known as transform
  fault boundary, sliding boundary, or conservative
  plate boundary).
• San Andres Fault in California is an example of
  transform boundary.

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15. Uplift

• This process result from convergent boudaries
  where land is being raised to a higher level, as
  during a period of mountain building.
• Examples of mountain ridges include the Rockies
  and the Himalayas.

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16. Volcanic Mountains

• Mountains formed when molten -lava rock- and
  other volcanic material reaches the Earths
  surface through a weak crustal area and piles up
  into a cone shaped structure.

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