8th Grade

1
8th Grade

• Science
• Plate Tectonics

2

• Geologists are scientists who study the forces
  that make and shape the planet Earth.
• Geologists study the Earths interior through
  seismic waves.

3

• Geologists discovered the Earth has three
  layers-the crust, the mantle, and the core.
• The oceanic crust beneath the ocean consists
  mostly of dense rock like basalt.
• Continental crust consists of less dense rock
  like granite.
• The upper mantle and crust make up the
  lithosphere.
• The asthenosphere is a soft layer that can bend
  like plastic.

4

• Heat is transferred in the mantle through
  radiation, conduction, and convection.
• Radiation is the transfer of heat through empty
  space.
• Conduction is heat transfer by direct contact of
  particles of matter.
• Convection is heat transfer by the movement of
  heated liquid.

5

• Alfred Wegener first proposed the theory of
  continental drift.
• Continental drift is Wegeners theory that all
  continents had once been joined together in a
  single landmass and have drifted apart since.
• Wegener named this supercontinent Pangaea.
• Wegeners theory was rejected by scientists
  because he could not explain what force pushes
  or pulls continents.

6
Fossils of tropical plants found on an island
in the Arctic Ocean are evidence for the theory
of continental drift.
7

• The mid-ocean ridge is the longest chain of
  mountains.
• Most of the mountains in the mid-ocean ridge lie
  hidden under hundreds of meters of water.
• Hess proposed that the ocean floors move,
  carrying the continents along with them. The
  movement begins at the mid-ocean ridge.
• At the mid-ocean ridge, molten material rises
  from the mantle and erupts.

8
The process that continually adds new material to
the ocean floor is called sea-floor spreading.
9

• The ocean floor plunges into deep underwater
  canyons called deep-ocean trenches.
• Subduction takes place in deep-ocean trenches.
• Subduction is the process by which the ocean
  floor sinks beneath a deep-ocean trench and back
  into the mantle.

10

• The lithosphere is broken into separate sections
  called plates.
• The geological theory that states that pieces of
  Earths lithosphere are in constant, slow motion,
  driven by convection currents in the mantle is
  plate tectonics.

11
GLE 5.2.B.c Describe (draw and write) how the
movement of crustal plates can cause earthquakes
and volcanic eruptions that can result in
mountain building and trench formation.

• Pangea is Evidence that plates move.
• See
• http//www.divediscover.whoi.edu/tectonics/pangea-
  animation.html
• http//www.geo.cornell.edu/hawaii/220/PRI/PRI_PT_c
  ontdrift.html
• Faults are breaks in the Earths crust where
  rocks have slipped past each other.

12

• There are three kinds of boundaries that explain
  plate movement.
• Understanding Plate motions
• Plate Tectonics II
• The place where two plates move apart or diverge
  is called a divergent boundary.
• A transform boundary is a place where two plates
  slip past each other, moving in opposite
  directions.

13

• When a divergent boundary develops on land, two
  of Earths plates slide apart.
• A deep valley called a rift valley forms along
  the divergent boundary.
• A convergent boundary is where two plates come
  together, or converge. The result of the plates
  hitting together is called a collision.

14
Practice MAP question

• Describe (draw and write) how the movement of
  crustal plates can cause earthquakes and volcanic
  eruptions that can result in mountain building
  and trench formation. Click on the links to see
  what kind of picture you should draw.
• Divergent boundaries -- where new crust is
  generated as the plates pull away from each
  other. This is where tectonic plates move away
  form each other. New curst is formed. Sea-floor
  spreading occurs.
• Convergent boundaries -- where crust is destroyed
  as one plate dives under another or pushes into
  one another. Crust can be melted and pushed up.
• Transform boundaries -- where crust is neither
  produced nor destroyed as the plates slide
  horizontally past each other.