2 Chapter 17. 1 Drifting Continents Describe one piece of early evidence to suggest that Earth’s continents may have once been joined.Discuss the evidence of continental drift.Explain why continental drift was not accepted when it was first proposed.
3 Early MapmakersMany early mapmakers thought Earth’s continents had moved based on matching coastlines.Some early mapmakers thought that the coastline of South America matched the coastline of Africa.
4 A meteorologist, by trade. Alfred WegenerA meteorologist, by trade.
5 Wegener’s EvidenceThe existence of coal beds in Antarctica indicates that the continent once had a temperate, rainy climate.
6 Wegener’s EvidenceGlossopteris is a fossil fern that helped support Wegener’s hypothesis of continental drift.
7 Alfred Wegener"Doesn't the east coast of South America fit exactly against the west coast of Africa, as if they had once been joined?“ - "This is an idea I'll have to pursue."Earth’s continents were once joined as a single landmass called Pangaea.
9 The Scientific Community Science’s Reaction "Utter, damned rot!" said the president of the prestigious American Philosophical Society."If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again," said another American scientist.Anyone who "valued his reputation for scientific sanity" would never dare support such a theory, said a British geologist.The ScientificCommunityScientists at the time rejected Wegener’s hypothesis of continental drift because he could not explain how or why Earth’s continents move.
11 Chapter 17. 2 Seafloor Spreading Explain the significance of magnetic patterns on the seafloor.Explain the process of seafloor spreading.Summarize the evidence that led to the discovery of seafloor spreading.
13 A map line connecting points that have the same age is an isochron. IsochronsA map line connecting points that have the same age is an isochron.
14 Isochrons (continued) Compared to ocean crust near deep-sea trenches, crusts near ocean ridges are younger .Isochrons (continued)
15 The study of Earth’s magnetic record is known as paleomagnetism.
16 Paleomagnetism (continued) The magnetic pattern of ocean-floor rocks on one side of an ocean ridge is a mirror image of that of the other side .
17 Seafloor SpreadingAs new seafloor moves away from an ocean ridge, the seafloor cools and becomes more dense than the material beneath it.
18 Seafloor Spreading 1) 2) 3) 5) 4) The seafloor contracts and sinks. Hot magma which is less dense than surrounding material, is forced toward the crust.3)Crust spreads along an ocean ridge and magma fills the gap that is created.5)New seafloor moves away from the ridge, cools, and becomes more dense than the material beneath it.4)New ocean floor forms as the magma hardens.
20 Chapter 17. 3 Theory of Plate Tectonics Explain the theory of plate tectonics.Compare and contrast the three types of plate boundaries and the features associated with each.Chapter Theory of Plate Tectonics
23 The TheoryThe theory of plate tectonics states that Earth’s crust and rigid upper mantle are broken into enormous slabs called plates that move slowly over Earth’s surface.
24 The Theory (Continued) According to the theory of plate tectonics, plates interact at plate boundaries by coming toward each other, moving away from each other, or moving horizontally past each other.
34 Chapter 17. 4 Causes of Plate Motion Explain the process of convection.Summarize how convection in the mantle is related to the movements of tectonic plates.Compare and contrast the processes of ridge push and slab pull.
35 ConvectionThe transfer of thermal energy by the movement of heated matter is convection.Convection currents transfer thermal energy from warmer regions to cooler regions.
36 Convection CurrentsThe driving forces of tectonic plates are related to convection currents in Earth’s mantle.
38 ReviewOceanic crust is composed mainly of basalt, and continental crust is composed mainly of granite.
39 Slab PullThe downward part of a convection current causes a sinking force that pulls tectonic plates toward one another .The weight of a subducting plate helps to pull the lithosphere into a subduction zone in a process called slab pull.
40 Ridge PushThe rising part of a convection current causes both upward and lateral forces that lift and split the lithosphere at a divergent boundary.
41 Convection and Tectonics To view this animation, click “View” and then “Slide Show” on the top navigation bar.
42 Forming a Divergent Boundary To view this animation, click “View” and then “Slide Show” on the top navigation bar.
43 Places where plates move apart are divergent boundaries. A long, narrow, fault-bounded, continental depression is a rift valley.BACK
44 Convergent Margins: India-Asia Collision To view this animation, click “View” and then “Slide Show” on the top navigation bar.
45 Plates come together at convergent boundaries. If two oceanic plates converge, a subduction zone forms.Subduction occurs when one tectonic plate descends beneath another.BACK
46 Transform FaultsTo view this animation, click “View” and then “Slide Show” on the top navigation bar.
47 Crust is neither destroyed nor formed along transform boundaries. Transform boundaries are places where plates slide horizontally past each other.BACK
49 Chapter 20 – Mountain Building Before I studied mountains,a mountain was just a mountain.While I studied mountains,a mountain was so much more than a mountain.When I understood mountains,-Zen Saying-
50 20.1 Crust-Mantle Relationships OBJECTIVESDescribe the elevation distribution of Earth’s surface.Explain isostasy and how it pertains to Earth’s mountains.Describe how Earth’s crust responds to the addition and removal of mass.
51 20.1 Earth’s TopographyThoughts? What is Earth’s highest elevation?What is Earth’s lowest elevation?
52 Majority of Topography About 70 % of Earth’s surface is below sea level.
53 IsostasyIsostasy between Earth’s mantle and crust exists when the mass of crust is balanced as a result of buoyancy and gravity.
54 DisplacementThe seafloor displaces more of the mantle than the same thickness of the continental crust.
55 Crust ThicknessContinental crust, because it is thicker than oceanic crust, rises higher above Earth’s surface.
56 Deepest RootMt. Everest is the tallest mountain on Earth, so it probably has the deepest root.
57 When mountains erode, their roots decrease in size. Isostatic ReboundWhen mountains erode, their roots decrease in size.In the process of isostatic rebound, mountains are eroded over hundreds of millions of years, while the crust below them rises.
58 Glacial IsostasyTo view this animation, click “View” and then “Slide Show” on the top navigation bar.
59 20.2 Convergent-Boundary Mountains OBJECTIVESCompare and contrast the different type of mountains that form along convergent plate boundaries.Explain how Appalachian Mountains formed.
60 The process that forms all mountains. OrogenyOrogenyThe process that forms all mountains.
61 Subduction ZonesSubduction results in the formation of deep-sea trenchs..
62 Convergent Zones Oceanic-Oceanic The volcanoes of an island arc complex form as a result of oceanic-oceanic convergence.At an oceanic-oceanic convergent boundary, old crust is recycled by subduction.
69 20.3 Other Types of Mountains OBJECTIVESDescribe the mountain ranges that form along ocean ridges.Compare and contrast up-lifted and fault-block mountains.Describe the mountains that form as a result of hot-spots in Earth’s mantle.
70 Divergent-Boundary Mountains Features found at divergent boundaries include ocean ridges .
71 Non-Boundary Mountains – Uplifted Uplifted mountains form when a large region of Earth’s crust rises up as a unit.
72 Uplifted mountains have rocks that are not very deformed. Uplifted (continued)Uplifted mountains have rocks that are not very deformed.
73 Uplifted mountains are the result of erosional forces. Uplifted (continued)Uplifted mountains are the result of erosional forces.
74 Uplifted (continued)The Adirondack Mountains, which are made of rocks that show little deformation, are uplifted mountains.
75 20.3 Non-Boundary Mountains – Fault Block Grand Tetons, WyomingFault-block mountains form when a large pieces of crust are dropped between large faults .
76 Non-Boundary Mountains – Volcanic Peaks Volcanoes that form over hot spots are often solitary and far from tectonic plate boundaries.The Hawaiian Islands formed as the result of the Pacific Plate’s moving over hot spots in Earth’s mantle.