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Chapter 4, Lesson 3, Theory of Plate Tectonics

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Presentation on theme: "Chapter 4, Lesson 3, Theory of Plate Tectonics"— Presentation transcript:

1 Chapter 4, Lesson 3, Theory of Plate Tectonics

2 Chapter 4, Lesson 3, Plate Tectonics Slide 1
*Main Idea ______________ -What are Earth’s plates? *Earth’s lithosphere is broken into large brittle pieces, which move as a result of forces acting upon them. ___________________________________________________ -Canadian geologist J. Tuzo Wilson used the term plates to describe the large pieces of Earth’s crust that move horizontally. -Wilson thought the plates were brittle and outlined by cracks. -The large brittle pieces of Earth’s outer shell are called lithospheric plates.

3 Chapter 4, Lesson 3, Plate Tectonics Slide 2
Earth’s lithospheric plates

4 Chapter 4, Lesson 3, Plate Tectonics Slide 3
*What is the theory of plate tectonics? *The theory of plate tectonics explains how lithospheric plates move and cause major geologic features and events on Earth’s surface. *Scientists from many countries developed the theory of plate tectonics. *This theory includes ideas from continental drift and seafloor spreading. *By the end of the 1960s, there was so much evidence supporting it that the theory gained acceptance by most scientists.

5 Chapter 4, Lesson 3, Plate Tectonics Slide 4
Which plate do you live on?

6 Chapter 4, Lesson 3, Plate Tectonics Slide 5
-What are boundaries of lithospheric plates? -Mid-ocean ridges show the boundaries of some lithospheric plates. -Thin lines of earthquake and volcanic eruptions define mid- ocean ridges. -Long and deep parts of the ocean seafloor are called ocean trenches. -In the ocean, there are thick bands of earthquakes and volcanoes that are located near ocean trenches. -Ocean trenches are what make up the rest of the plate boundaries.

7 Chapter 4, Lesson 3, Plate Tectonics Slide 6
*What are the types of lithosphere? *In Chapter 2, you read that the lithosphere is made of both the crust and the upper mantle, which is made of rigid and brittle rocks. *Just like there are two different types of crust, there are two different types of lithosphere. *Oceanic lithosphere is much thinner and denser than continental lithosphere. *Oceanic lithosphere is made mainly of the dense igneous rocks, basalt and gabbro

8 Chapter 4, Lesson 3, Plate Tectonics Slide 7
*What are the types of lithosphere? (continued) *In contrast, continental lithosphere contains the continental crust, which is made of igneous rocks such as granite and metamorphic rocks such as gneiss. *Most of the rocks in the continental lithosphere are less dense than the rocks in the oceanic lithosphere. *Most of the plates contain both oceanic and continental lithosphere.

9 Chapter 4, Lesson 3, Plate Tectonics Slide 8
Continental and oceanic lithospheres

10 Chapter 4, Lesson 3, Plate Tectonics Slide 9
-What controls plate movement? -Heat has been escaping from Earth since it first formed. -Convection currents in the mantle provide matter and energy for the motion of the plates. -A supply of internal heat in Earth creates the convection currents. -Temperatures in Earth increases with increasing depth. -Inside Earth’s crust there are some elements, such as uranium and potassium, that are radioactive.

11 Chapter 4, Lesson 3, Plate Tectonics Slide 10
-What controls plate movement? (continued) -As radioactive elements decay, they produce heat, along with radiation, in rocks that contain them. -The heat increases the temperature of the surrounding rock, causing its density to decrease. -This causes movement of both rock and heat from inside Earth toward the surface.

12 Chapter 4, Lesson 3, Plate Tectonics Slide 11
*How does convection effect plate movement? *Some scientists hypothesize that convection currents in Earth’s mantle drive plate movement. *They think that the brittle lithospheric plates float, like a sheet of ice over water, on top of the asthenosphere. *Eventually, a cooler, denser lithospheric plate sinks under another plate and into the mantle. *A plate that sinks back into the mantle is called a slab. *The slab bends and breaks as it sinks down causing earthquakes.

13 Chapter 4, Lesson 3, Plate Tectonics Slide 12
*How does convection effect plate movement? (continued) *Along a mid-ocean ridge, less dense rock is brought near the surface and melts. *At the surface, new oceanic lithosphere forms at the ridge and as the rock cools, it becomes denser. *The new plate starts to move away from the ridge with the convection current

14 Chapter 4, Lesson 3, Plate Tectonics Slide 13
-What is ridge push and slab pull? -The force of gravity tends to move things downhill. -Some scientists believe that is what happens to a lithospheric plate along a ridge. -The force of gravity moves the plate downward and away from the ridge. -This force is known as a ridge push. -Slab pull occurs when a lithospheric plate sinks into the mantle.

15 Chapter 4, Lesson 3, Plate Tectonics Slide 14
Ridge push and slab pull

16 Chapter 4, Lesson 3, Plate Tectonics Slide 15
*How do scientists measure plate movement? *Scientists use satellites to measure plate movement. *Global Positioning Systems (GPS) is a network of satellites used to determine locations on Earth. *Because GPS can be used to accurately measure distances, it can also be used to measure the movement of plates. *Scientists have set up a group of computer receivers to monitor plate movement around the world. *Another satellite system, Satellite Laser Ranging (SLR), uses pulses of light to measure distances.

17 Chapter 4, Lesson 3, Plate Tectonics Slide 16
*How do scientists measure plate movement? (continued) *Using satellite data from these methods, scientists have estimated the rates at which lithospheric plates move. *The results from GPS and SLR show that the plates are moving only centimeters per year.

18 Chapter 4, Lesson 3, Plate Tectonics Slide 16
-How are plate tectonics and the rock cycle related? -Rocks are always moving through the rock cycle. -Magma will rise up to Earth’s surface to become igneous rock at a mid-ocean ridge. -A plate will slowly move away from the ridge and cool while it carries the igneous rock with it. -Eventually, the plate will sink into the mantle. -As plates move, they recycle material by keeping it moving through the rock cycle.

19 Chapter 4, Lesson 3, Plate Tectonics Slide 17
*Summary *Earth’s outer shell is broken into large, brittle pieces called lithospheric plates. *The thickness and composition of lithospheric plates depend upon whether the plate is made of oceanic or continental material. *Earthquakes and volcanoes occur along the boundaries of lithospheric plates. *The theory of plate tectonics explains how lithospheric plates move and cause major geologic features and events on Earth’s surface.


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