Earth Science

Plate Tectonics

Merrill Chapter 13 Notes

13-1 Structure of Earth

 

Earth’s interior is made mostly of rock-but not all of it is solid.

Rock forms 4 main layers in the Earth Use the Peach Model to help you see it!!!!

  1. Inner Core: solid, great pressure and heat-compressed of very dense iron and nickel
  2. Outer Core: liquid, composed of iron and nickel.
  3. Mantle: largest layer composed of primarily silicon, oxygen, magnesium, and iron. Plastic-like layer, kind of like taffy.
  4. Crust: varies in thickness (mountain region thick, ocean bottom thin)

 

13-2 Science and New Ideas

Continental Drift: states that continents have moved horizontally to their current locations. First proposed by Alfred Wagner.

1.      Pangea: supercontinent

 

13-3 Evidence for Continental Drift

1. Fossil and Climate clues: be able to identify and describe these.

2. Rock clues: be able to identify and describe these.

 

The mid-ocean ridges form an underwater mountain range that extends through the center of the Earth’s oceans. Why?

Sea Floor Spreading:  Hess offered an explanation for these MOR’s.

  1. Hot, less dense material in the mantle is forced upward to the surface of a mid-ocean ridge.
  2. It then flows sideways, carrying the seafloor away form the ridge in both directions. See Figure 13-7
  3. New seafloor spreads out, cools, and becomes more dense then the underlying plastic-like layer below it. Thus it begins to sink, forming trenches.

 

Evidence for Sea Floor Spreading:

1. Age of the sea floor. The oldest rock in the sea floor is about 160 million years old.

            However, on the continents, some rock is almost 4 billion years old. ?

 

2. Youngest sea floor rock is nearest the MOR’s.

3. Magnetic Clues: identical magnetic patterns in rocks the same distance away on both            

            sides of the MOR’s.

 

 

 

 

 

 

13-4 Theory of Plate Tectonics

1. States that Earth’s crust and upper mantle are broken into sections called plates.

2. The plates move or float on the mantle.

3. Plates are composed of the crust and a part of the upper mantle.

4. The two parts together are called the lithosphere. (about 100 km thick and less dense then the layer below it.

5. The plasticlike layer below the lithosphere is the asthenosphere.

6. The lithospheric plates float on the asthenosphere because of the difference in densities.

7. Variety of movements.

8. Produce mountains, earthquakes, and volcanoes (tectonic activities)

 

Plate Boundaries:

Divergent Boundaries: the boundary between two plates that are moving apart from one another. This occurs at MOR’s.

 

Convergent Boundaries: the boundary between two different plates that are colliding. At this type of boundary crustal material is lost at the same rate that it is being added at the MOR’s. Crustal material from one plate is being subducted under the other plate.

-The area where an oceanic plate descends into the upper mantle is called a subduction zone. Volcanoes occur at subduction zones.

 

3 types of Convergent Boundaries: Figure 13-11 (test questions)*******

  1. An oceanic plate (OP) is subducted under a continental plate (CP). Results in volcanic action and crustal uplift. (Andes Mtns)
  2. An OP is subducted under an OP. Forms trenches.
  3. A CP collides with a CP. The leading edge is buckled rather then subducted (because they have the same density). Creates mountain ranges. Himalayas

 

Transform Fault Boundaries: occur when two plates slide by each other. The San Andreas Fault.

 

Causes of Plate Tectonics:

Giant convection currents within the mantle carry the plates along. Different temperatures cause different densities that create these Convection Currents in the mantle. See Figure 13-13 in the text.