chapter: plate tectonics
DESCRIPTION
Table of Contents. Chapter: Plate Tectonics. Section 1: Continental Drift. Section 2: Seafloor Spreading. Section 3: Theory of Plate Tectonics. Continental Drift. 1. Evidence for Continental Drift. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/1.jpg)
![Page 2: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/2.jpg)
Chapter: Plate Tectonics
Table of ContentsTable of Contents
Section 3: Theory of Plate Tectonics
Section 1: Continental Drift
Section 2: Seafloor Spreading
![Page 3: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/3.jpg)
Evidence for Continental Drift• If you look at a map of Earth’s surface, you
can see that the edges of some continents look as though they could fit together like a puzzle.
11Continental DriftContinental Drift
![Page 4: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/4.jpg)
Pangaea
• German meteorologist Alfred Wegener (VEG nur) proposed the hypothesis of continental drift.
11Continental DriftContinental Drift
• According to the hypothesis of continental drift, continents have moved slowly to their current locations.
![Page 5: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/5.jpg)
Pangaea• Wegener suggested that all continents once
were connected as one landmass that broke apart about 200 million years ago.
11Continental DriftContinental Drift
• He called this large landmass Pangaea (pan JEE uh), which means “all land.”
![Page 6: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/6.jpg)
A Controversial Idea
• Wegener’s ideas about continental drift were controversial.
11Continental DriftContinental Drift
• It wasn’t until long after Wegener’s death in 1930 that his basic hypothesis was accepted.
Click image to view movie.
![Page 7: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/7.jpg)
A Controversial Idea
• He was unable to explain exactly how the continents drifted apart.
11Continental DriftContinental Drift
• He proposed that the continents plowed through the ocean floor, driven by the spin of Earth.
![Page 8: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/8.jpg)
A Controversial Idea
• Physicists and geologists of the time pointed out that continental drift would not be necessary to explain many of Wegener’s observations.
11Continental DriftContinental Drift
![Page 9: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/9.jpg)
Fossil Clues
• Fossils provided support for continental drift.
11Continental DriftContinental Drift
• Fossils of the reptile Mesosaurus have been found in South America and Africa.
![Page 10: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/10.jpg)
Fossil Clues
• This swimming reptile lived in freshwater and on land.
11Continental DriftContinental Drift
• How could fossils of Mesosaurus be found on land areas separated by a large ocean of salt water?
• Wegener hypothesized that this reptile lived on both continents when they were joined.
![Page 11: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/11.jpg)
A Widespread Plant
• Another fossil that supports the hypothesis of continental drift is Glossopteris (glahs AHP tur us).
11Continental DriftContinental Drift
• This fossil plant has been found in Africa, Australia, India, South America, and Antarctica.
![Page 12: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/12.jpg)
A Widespread Plant
• The presence of Glossopteris in so many area also supported Wegener’s idea that all of these regions once were connected and had similar climates.
11Continental DriftContinental Drift
![Page 13: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/13.jpg)
Climate Clues
• Fossils of warm-weather plants were found on the island of Spitsbergen in the Arctic Ocean.
11Continental DriftContinental Drift
• To explain this, Wegener hypothesized that Spitsbergen drifted from tropical regions to the arctic.
![Page 14: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/14.jpg)
Climate Clues
• Glacial deposits and rock surfaces scoured and polished by glaciers are found in South America, Africa, India, and Australia.
11Continental DriftContinental Drift
• This shows that parts of these continents were covered with glaciers in the past.
![Page 15: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/15.jpg)
Rock Clues• Similar rock structures are
found on different continents.
11Continental DriftContinental Drift
• Parts of the Appalachian Mountains of the eastern United States are similar to those found in Greenland and western Europe.
• Rock clues like these support the idea that the continents were connected in the past.
![Page 16: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/16.jpg)
How could continents drift?
• Although Wegener provided evidence to support his hypothesis of continental drift, he couldn’t explain how, when, or why these changes took place.
11Continental DriftContinental Drift
![Page 17: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/17.jpg)
How could continents drift?
• Because other scientists could not provide explanations either, Wegener’s idea of continental drift was initially rejected.
11Continental DriftContinental Drift
• Rock, fossil, and climate clues were the main types of evidence for continental drift.
![Page 18: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/18.jpg)
How could continents drift?
• After Wegener’s death, more clues were found, largely because of advances in technology, and new ideas that related to continental drift were developed.
11Continental DriftContinental Drift
![Page 19: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/19.jpg)
11Section CheckSection Check
Question 1
__________ is the hypothesis that continents have slowly moved to their current locations.
A. Continental driftB. Mid-ocean shiftingC. PangaeaD. Seafloor spreading
![Page 20: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/20.jpg)
11Section CheckSection Check
Answer
The answer is A. Continental drift is the theory that the continents have slowly moved. Seafloor spreading is a process that would help explain how the continental drift might occur.
![Page 21: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/21.jpg)
11Section CheckSection Check
Question 2
Who proposed the hypothesis of continental drift?
A. EskerB. GagarinC. HessD. Wegener
![Page 22: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/22.jpg)
11Section CheckSection Check
Answer
The answer is D. Wegener proposed the hypothesis of continental drift. Hess theorized that the seafloor is spreading.
![Page 23: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/23.jpg)
11Section CheckSection Check
Question 3
What is Pangaea?
![Page 24: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/24.jpg)
11Section CheckSection Check
Answer
Pangaea means “all land” and is the name that Wegener used to refer to the one large landmass that he believed existed before it broke apart into continents.
![Page 25: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/25.jpg)
Mapping the Ocean Floor
• If you were to lower a rope from a boat until it reached the seafloor, you could record the depth of the ocean at that particular point.
• This is exactly how it was done until World War I, when the use of sound waves was introduced by German scientists to detect submarines.
22Seafloor SpreadingSeafloor Spreading
![Page 26: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/26.jpg)
Mapping the Ocean Floor• Sound waves echo off the ocean bottom—the
longer the sound waves take to return to the ship, the deeper the water is.
• Using sound waves, researchers discovered an underwater system of ridges, or mountains, and valleys like those found on the continents.
22Seafloor SpreadingSeafloor Spreading
![Page 27: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/27.jpg)
Mapping the Ocean Floor
• In some of these underwater ridges are rather long rift valleys where volcanic eruptions and earthquakes occur from time to time.
• In the Atlantic, the Pacific, and in other oceans around the world, a system of ridges, called the mid-ocean ridges, is present.
22Seafloor SpreadingSeafloor Spreading
![Page 28: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/28.jpg)
The Seafloor Moves
• In the early 1960s, Princeton University scientist Harry Hess suggested an explanation.
• His now-famous theory is known as seafloor spreading.
22Seafloor SpreadingSeafloor Spreading
![Page 29: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/29.jpg)
The Seafloor Moves
• Hess proposed that hot, less dense material below Earth’s crust rises toward the surface at the mid-ocean ridges.
• Then, it flows sideways, carrying the seafloor away from the ridge in both directions.
22Seafloor SpreadingSeafloor Spreading
![Page 30: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/30.jpg)
The Seafloor Moves• As the seafloor spreads apart at a mid-ocean
ridge, new seafloor is created. • The older
seafloor moves away from the ridge in opposite directions.
22Seafloor SpreadingSeafloor Spreading
![Page 31: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/31.jpg)
Evidence for Spreading
• In 1968, scientists aboard the research ship Glomar Challenger began gathering information about the rocks on the seafloor.
• Scientists found that the youngest rocks are located at the mid-ocean ridges.
22Seafloor SpreadingSeafloor Spreading
![Page 32: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/32.jpg)
Evidence for Spreading• The ages of rocks become increasingly older
in samples obtained farther from the ridges, adding to the evidence for seafloor spreading.
22Seafloor SpreadingSeafloor Spreading
• As molten material is forced upward along the ridges, it bringsheat and chemicals that support exotic life-forms in deep, ocean water.
![Page 33: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/33.jpg)
Magnetic Clues
• During a magnetic reversal, the lines of magnetic force run the opposite way.
• Scientists have determined that Earth’s magnetic field has reversed itself many times in the past.
22Seafloor SpreadingSeafloor Spreading
• The reversals are recorded in rocks forming along mid-ocean ridges.
![Page 34: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/34.jpg)
Magnetic Time Scale
• Whenever Earth’s magnetic field reverses, newly forming iron minerals will record the magnetic reversal.
• Using a sensing device called a magnetometer (mag nuh TAH muh tur) to detect magnetic fields, scientists found that rocks on the ocean floor show many periods of magnetic reversal.
22Seafloor SpreadingSeafloor Spreading
![Page 35: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/35.jpg)
Magnetic Time Scale
• The magnetic alignment in the rocks reverses back and forth over time in strips parallel to the mid-ocean ridges.
• A strong magnetic reading is recorded when the polarity of a rock is the same as the polarity of Earth’s magnetic field today.
22Seafloor SpreadingSeafloor Spreading
![Page 36: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/36.jpg)
Magnetic Time Scale
• This discovery provided strong support that seafloor spreading was indeed occurring.
• This helped explain how the crust could move—something that the continental drift hypothesis could not do.
22Seafloor SpreadingSeafloor Spreading
![Page 37: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/37.jpg)
22Section CheckSection Check
Question 1
What is seafloor spreading?
![Page 38: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/38.jpg)
22Section CheckSection Check
AnswerSeafloor spreading is the process in which hot, less dense material below Earth’s crust rises toward the surface at the mid-ocean ridges. This material flows sideways and carries the seafloor away from the ridge in both directions.
![Page 39: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/39.jpg)
22Section CheckSection Check
Question 2
What method of mapping the ocean floor was developed by scientists in the 1940s and 1950s?
Answer
In the 1940s and 1950s, scientists began to use sound waves echoing off the ocean bottom to map large areas of the ocean floor in detail.
![Page 40: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/40.jpg)
22Section CheckSection Check
Question 3What was the significance of the discovery that the magnetic alignment in rocks on the ocean floor reverses back and forth in strips parallel to mid-ocean ridges?
![Page 41: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/41.jpg)
22Section CheckSection Check
Answer
The magnetic reversals showed that new rock was being formed at the mid-ocean ridges, and helped explain how the crust could move.
![Page 42: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/42.jpg)
Plate Tectonics
• The idea of seafloor spreading showed that more than just continents were moving, as Wegener had thought.
• It was now clear to scientists that sections of the seafloor and continents move in relation to one another.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 43: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/43.jpg)
Plate Movements
• According to the theory of plate tectonics, Earth’s crust and part of the upper mantle are broken into sections.
• These sections, called plates, move on a plasticlike layer of the mantle.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 44: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/44.jpg)
Composition of Earth’s Plates• Plates are made of the crust and a part of the
upper mantle.
• These two parts combined are the lithosphere (LIH thuh sfihr).
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 45: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/45.jpg)
Composition of Earth’s Plates• The plasticlike layer below the lithosphere
is called the asthenosphere (as THE nuh sfihr).
• The rigid plates of the lithosphere float and move around on the asthenosphere.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 46: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/46.jpg)
Plate Boundaries
• When plates move, they can interact in several ways.
• They can move toward each other and converge, or collide.
33Theory of Plate TectonicsTheory of Plate Tectonics
• They also can pull apart or slide alongside one another. When the plates interact, the result of their movement is seen at the plate boundaries.
![Page 47: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/47.jpg)
Plate Boundaries• Movement along any plate boundary means
that changes must happen at other boundaries.
33Theory of Plate TectonicsTheory of Plate Tectonics
• What is happening to the Atlantic Ocean floor between the North American and African Plates?
![Page 48: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/48.jpg)
Plates Moving Apart• The boundary between two plates that are
moving apart is called a divergent boundary. • In the Atlantic
Ocean, the North American Plate is moving away from the Eurasian and the African Plates.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 49: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/49.jpg)
Plates Moving Apart33
Theory of Plate TectonicsTheory of Plate Tectonics
• That divergent boundary is called the Mid-Atlantic Ridge.
![Page 50: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/50.jpg)
Plates Moving Together
• As new crust is added in one place, it disappears below the surface at another.
• The disappearance of crust can occur when seafloor cools, becomes denser, and sinks.
33Theory of Plate TectonicsTheory of Plate Tectonics
• This occurs where two plates move together at a convergent boundary.
![Page 51: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/51.jpg)
Plates Moving Together
• When an oceanic plate converges with a less dense continental plate, the denser oceanic plate sinks under the continental plate.
• The area where an oceanic plate subducts, or goes down, into the mantle is called a subduction zone.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 52: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/52.jpg)
Plates Moving Together
• Some volcanoes form above subduction zones.
• This type of convergent boundary creates a deep-sea trench where one plate bends and sinks beneath the other.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 53: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/53.jpg)
Plates Moving Together
• High temperatures cause rock to melt around the subducting slab as it goes under the other plate.
• The newly formed magma is forced upward along these plate boundaries, forming volcanoes.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 54: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/54.jpg)
Where Plates Collide
• A subduction zone also can form where two oceanic plates converge.
• In this case, the colder, older, denser oceanic plate bends and sinks down into the mantle.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Usually, no subduction occurs when two continental plates collide.
![Page 55: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/55.jpg)
Where Plates Collide• Because both of these plates are less dense
than the material in the asthenosphere, the two plates collide and crumple up, forming mountain ranges.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Earthquakes are common at these convergent boundaries.
![Page 56: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/56.jpg)
Where Plates Slide Past Each Other
• The third type of plate boundary is called a transform boundary.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Transform boundaries occur where two plates slide past one another.
• They move in opposite directions or in the same direction at different rates.
![Page 57: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/57.jpg)
• When one plate slips past another suddenly, earthquakes occur.
33Theory of Plate TectonicsTheory of Plate Tectonics
• The San Andreas Fault is part of a transform plate boundary. It has been the site of many earthquakes.
Where Plates Slide Past Each Other
![Page 58: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/58.jpg)
Causes of Plate Tectonics— Convection Inside Earth
• The cycle of heating, rising, cooling, and sinking is called a convection current.
33Theory of Plate TectonicsTheory of Plate Tectonics
• A version of this same process, occurring in the mantle, is thought to be the force behind plate tectonics.
• Scientists suggest that differences in density cause hot, plasticlike rock to be forced upward toward the surface.
![Page 59: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/59.jpg)
Moving Mantle Material
• In one hypothesis, convection currents occur throughout the mantle.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Such convection currents (see arrows) are the driving force of plate tectonics.
![Page 60: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/60.jpg)
Features Caused by Plate Tectonics
• As plates move, they interact.
33Theory of Plate TectonicsTheory of Plate Tectonics
• The interaction of plates produces forces that build mountains, create ocean basins, and cause volcanoes.
![Page 61: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/61.jpg)
Features Caused by Plate Tectonics
• When rocks in Earth’s crust break and move, energy is released in the form of seismic waves.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Humans feel this release as earthquakes.
![Page 62: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/62.jpg)
Normal Faults and Rift Valleys• When rocks break and move along surfaces,
a fault forms.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Faults interrupt rock layers by moving them out of place.
• Entire mountain ranges can form in the process, called fault-block mountains
![Page 63: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/63.jpg)
Normal Faults and Rift Valleys• Rift valleys and mid-ocean ridges can form
where Earth’s crust separates.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Examples of rift valleys are the Great Rift Valley in Africa, and the valleys that occur in the middle of mid-ocean ridges.
Click image to view movie.
![Page 64: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/64.jpg)
Mountains and Volcanoes• As continental
plates collide, the forces that are generated cause massive folding and faulting of rock layers into mountain ranges such as the Himalaya.
33Theory of Plate TectonicsTheory of Plate Tectonics
![Page 65: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/65.jpg)
Mountains and Volcanoes• The type of faulting produced is generally
reverse faulting.
33Theory of Plate TectonicsTheory of Plate Tectonics
• When two oceanic plates converge, the denser plate is forced beneath the other plate.
• Curved chains of volcanic islands called island arcs form above the sinking plate.
![Page 66: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/66.jpg)
Mountains and Volcanoes
• If an oceanic plate converges with a continental plate, the denser oceanic plate slides under the continental plate.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Folding and faulting at the continental plate margin can thicken the continental crust to produce mountain ranges.
![Page 67: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/67.jpg)
Strike-Slip Faults• In a strike-slip fault, rocks on opposite sides
of the fault move in opposite directions, or in the same direction at different rates.
33Theory of Plate TectonicsTheory of Plate Tectonics
• When plates move suddenly, vibrations are generated inside Earth that are felt as an earthquake.
![Page 68: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/68.jpg)
Testing for Plate Tectonics
• Until recently, the only tests scientists could use to check for plate movement were indirect.
33Theory of Plate TectonicsTheory of Plate Tectonics
• They could study the magnetic characteristics of rocks on the seafloor.
• They could study volcanoes and earthquakes.
![Page 69: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/69.jpg)
Testing for Plate Tectonics• One new method uses lasers and a satellite.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Now, scientists can measure exact movementsof Earth’s plates of as little as 1 cm per year.
![Page 70: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/70.jpg)
Current Data
• Satellite Laser Ranging System data show that Hawaii is moving toward Japan at a rate of about 8.3 cm per year.
33Theory of Plate TectonicsTheory of Plate Tectonics
• Using such methods, scientists have observed that the plates move at rates ranging from about 1 cm to 12 cm per year.
![Page 71: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/71.jpg)
33Section CheckSection Check
Question 1
Which of the following is made up of Earth’s crust and part of the upper mantle?
A. asthenosphereB. continental crustC. lithosphereD. plastisphere
![Page 72: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/72.jpg)
33Section CheckSection Check
Answer
The answer is C. The asthenosphere is the plasticlike layer below the lithosphere.
![Page 73: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/73.jpg)
33Section CheckSection Check
Question 2
________ is the theory that Earth’s crust and part of the upper mantle are broken into sections.
A. Continental driftB. Pangaea effectC. Plate tectonicsD. Seafloor spreading
![Page 74: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/74.jpg)
33Section CheckSection Check
Answer
The answer is C. The sections are called plates and are thought to move on a plasticlike layer of Earth’s mantle.
![Page 75: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/75.jpg)
33Section CheckSection Check
Question 3
The boundary between two plates that are moving apart is a __________ boundary.
A. convergentB. creepingC. divergentD. tectonic
![Page 76: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/76.jpg)
33Section CheckSection Check
Answer
The answer is C. An example of a divergent boundary is the Mid-Atlantic Ridge, where the seafloor is spreading.
![Page 77: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/77.jpg)
To advance to the next item or next page click on any of the following keys: mouse, space bar, enter, down or forward arrow.
Click on this icon to return to the table of contents
Click on this icon to return to the previous slide
Click on this icon to move to the next slide
Click on this icon to open the resources file.
HelpHelp
Click on this icon to go to the end of the presentation.
![Page 78: Chapter: Plate Tectonics](https://reader035.vdocuments.mx/reader035/viewer/2022062321/56813561550346895d9cc846/html5/thumbnails/78.jpg)
End of Chapter Summary File