1. Summary

This video discusses the constant motion of the earth’s lithospheric plates known as plate tectonics. It talks about the different types of plates as well as the different ways that the plates interact with one another at plate boundaries. Finally, this video discusses earthquakes, mountains, and trenches and how these geological features result from plate tectonics.

2. Why Watch This Video?

1. Have you ever wondered how transform, convergent, and divergent boundaries function? This video addresses each boundary as well as the different geological features that are created as a result of these boundaries.

2. Would you like to know more about the different layers of the earth? This video offers a visual aid which labels each of the earth’s layers and also discusses key features of each layer.

3. Have you ever been confused about why some parts of the earth sit above sea level while others sit much farther below at the bottom of the ocean? This video explains why the composition of the earth’s continental and oceanic crust differs.

3. Key Terms

Lithosphere – The lithosphere is the stiff outer coat of the earth. This cool layer is divided into a variety of plates. The plates can either be oceanic and are found under the ocean, or continental meaning they are helping to make up part of a continent. They can also be a combination of the two.

Plate Boundaries: Plate boundaries exist where two or more different lithospheric plates meet. There are three different types of boundaries:

  • Transform Boundaries – plates glide past each other
  • Divergent Boundaries – plates move away from each other
  • Convergent Boundaries – plates push against each other

Subduction: Subduction occurs at convergent boundaries. When two plates are pushing against each other, the denser plate will be forced under the lighter one. Due to force and gravitational pull, that plate will sink. This process is known as subduction. However, if the two converging plates are both continental, the plates will instead press upward, resulting in the formation of mountains.

4. Loose Ends

Loose end #1: What is the role of the asthenosphere? The asthenosphere plays a key role in plate tectonics. The intense heat let off by the earth’s core causes it to be very warm and supple. This allows the upper mantle and earth’s crust to move over it.

Loose end #2: Why do the earth’s plates move? Plates on the earth’s outer surface move due to heat and gravity. The earth’s core heats the mantle which causes convection cells to either move up or down, depending on density. Gravitational pull also causes movement in the earth’s plates. When two plates meet, the heavier plate will be forced to move under the lighter plate. This process is known as subduction.

Loose end #3: How do earthquakes occur at transform boundaries if the plates are sliding past one another? Although the plates at transform boundaries are sliding past one another, there can still a considerable amount of friction between the two plates. This resistance can cause a sudden slip or rock to break which results in an earthquake.

5. Self-Test Questions

Question 1: ________________ boundaries occur where two plates slide past one another
a) Convergent
b) Transform
c) Lithospheric
d) Divergent

Question 2: How thick is typical oceanic crust?
a) 50km
b) 140km
c) 8km
d) 500km

Question 3: The earth’s most powerful earthquakes typically occur on which type of boundary?
a) Convergent
b) Transform
c) Divergent
d) Continental

Question 4: What happens when one oceanic plate subducts under another oceanic plate?
a) Nothing, the two plates get stuck
b) An ocean trench forms
c) The ocean produces a sinkhole
d) There is a tsunami

Question 5: At divergent boundaries, which substance melts to create the earth’s crust?
a) The earth’s mantle
b) Dirt and debris
c) Iron
d) The earth’s core

6. Answers to Self-Test Questions

1. Correct Answer: B) Transform boundaries exist where plates move horizontally against one another. They are also referred to as strike-slip boundaries.

2. Correct Answer: C) Oceanic crust is only around 8km thick. It is denser than continental crust because it contains more magnesium and iron. Alternatively, continental crust has an average thickness of 40km. It is less dense than oceanic crust because it is made up of granitic, sedimentary and metamorphic rocks.

3. Correct Answer: A) Convergent boundaries. Most of the earth’s intense earthquakes occur at convergent boundaries because this is where two lithospheric plates will have collided. The sheer force of the collision will cause earthquakes that can reach up to magnitude 9.

4. Correct Answer: B) An ocean trench forms acting as a feature to denote where one oceanic place has been pushed down by another one into the earth’s mantle.

5. Correct Answer: A) The mantle. A small amount of the earth’s mantle melts to create a new crust where two plates have pulled away from each other.

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Item Credit: Incorporated Research Institutions For Seismology (IRIS)

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