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Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Wegener’s Hypothesis Continental drift the hypothesis.

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1 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Wegener’s Hypothesis Continental drift the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present location The hypothesis of continental drift was first proposed by German scientist Alfred Wegener in 1912. Wegener used several different types of evidence to support his hypothesis Section 1 Continental Drift

2 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu An Idea Before Its Time 9.1 Continental Drift  Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent. Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.

3 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Breakup of Pangaea

4 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Wegener’s Hypothesis, continued Wegener’s Evidence Fossil Evidence: fossils of the same plants and animals could be found in areas of continents that had once been connected. Evidence from Rock Formations: ages and types of rocks in the coastal regions of widely separated areas matched closely. Section 1 Continental Drift

5 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Climatic Evidence: changes in climatic patterns suggested the continents had not always been located where they are now.

6 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Wegener’s Hypothesis, continued Similar rock formations and fossil evidence supported Wegener’s hypothesis. Section 1 Continental Drift

7 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

8 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Wegener’s Hypothesis, continued Missing Mechanisms Wegener proposed that the continents moved by plowing through the rock of the ocean floor. Wegener’s ideas were strongly opposed. Wegener’s mechanism was disproved by geologic evidence. Wegener spent the rest of his life searching for a mechanism for the movement of continents. Section 1 Continental Drift

9 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Rejecting the Hypothesis 9.1 Continental Drift  A New Theory Emerges Wegener could not provide an explanation of exactly what made the continents move. News technology lead to findings which then lead to a new theory called plate tectonics.

10 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Mid-Ocean Ridges Mid-ocean ridge a long, undersea mountain chain that has a steep, narrow valley at its center, that forms as magma rises from the asthenosphere, and that creates new oceanic lithosphere (sea floor) as tectonic plates move apart Section 1 Continental Drift

11 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Mid-Ocean Ridges, continued In 1947, a group of scientists set out to map the Mid- Atlantic Ridge. While studying the Mid-Atlantic Ridge, scientists noticed two surprising trends. 1.The sediment that covers the sea floor is thinner closer to a ridge than it is farther from the ridge 2.The ocean floor is very young. Rocks on land are as old as 3.8 billion years. None of the oceanic rocks are more than 175 million years old. Section 1 Continental Drift

12 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Mid-Ocean Ridges, continued Rocks closer to a mid-ocean ridge are younger than rocks farther from the ridge. Rocks closer to the ridge are covered with less sediment than rocks farther from the ridge. Section 1 Continental Drift

13 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Sea-Floor Spreading Sea-floor spreading the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge Paleomagnetism the study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth’s magnetic poles; also the magnetic properties that rock acquires during formation Section 1 Continental Drift

14 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Sea-Floor Spreading, continued In the late 1950’s geologist Harry Hess proposed that the valley at the center of the mid-ocean ridge was a crack, or rift, in Earth’s crust. As the ocean floor moves away from the ridge, molten rock, or magma, rises to fill the crack. Hess suggested that if the sea floor is moving, the continents might be moving also. He suggested this might be the mechanism that Wegener was searching for. Section 1 Continental Drift

15 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Sea-Floor Spreading, continued Section 1 Continental Drift

16 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Sea-Floor Spreading, continued As the ocean floor spreads apart, magma rises to fill the rift and then cools to form new rock. Section 1 Continental Drift

17 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Sea-Floor Spreading, continued Section 1 Continental Drift

18 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evidence for Plate Tectonics 9.4 Testing Plate Tectonics  Paleomagnetism is the natural remnant magnetism in rock bodies; this permanent magnetization acquired by rock can be used to determine the location of the magnetic poles at the time the rock became magnetized. Normal polarity—when rocks show the same magnetism as the present magnetism field Reverse polarity—when rocks show the opposite magnetism as the present magnetism field

19 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Polarity of the Ocean Crust

20 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Paleomagnetism, continued Magnetic Symmetry The pattern of magnetic symmetry and age of rock formation indicate that new rock forms at the center of a ridge and then move away from the center in opposite directions. Section 1 Continental Drift

21 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion 1.Convection Warm fluids in the mantle are less dense and rise to the surface. Cooler fluids sink away from the surface. This drags the plates with the currents. 2.Density the plate with the higher density will sink below the less dense plate. Oceanic crust is thinner, but more dense than continental crust, so oceanic crust will sink below continental crust. This is called subduction.

22 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

23 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued The convection process can be modeled by boiling water in a pot on the stove. As the water at the bottom of the pot is heated, the water at the bottom expands and becomes less dense than the cooler water above it. The cooler, denser water sinks, and the warmer water rises to the surface to create a cycle called a convection cell.

24 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued Mantle Convection As the hot material rises, the cooler, denser material flows away from the hot material and sinks into the mantle to replace the rising material. As the mantle material moves, it drags the overlying tectonic plates along with it.

25 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued Insert TT

26 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued Insert TT

27 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued Formation of Pangaea The supercontinent Pangaea formed about 300 million years ago. Several mountain ranges, such as the Appalachian Mountains and the Ural Mountains formed during the collisions that created Pangaea. A body of water called the Tethys Sea cut into the eastern edge of Pangaea. The single, large ocean that surrounded Pangaea was called Panthalassa.

28 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued

29 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued

30 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued Breakup of Pangaea About 250 million years ago (during the Paleozoic Era), Pangaea began to break into two continents— Laurasia and Gondwanaland. Laurasia became the continents of North America and Eurasia. Gondwanaland became the continents of Africa, South America, India, Australia, and Antarctica.

31 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued

32 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued The Modern Continents Slowly, the continents moved into their present positions. As the continents drifted, they collided with terranes and other continents. New mountain ranges, such as the Rocky Mountains, the Andes, and the Alps, formed. Tectonic plate motion also caused new oceans to open up and caused others to close.

33 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued

34 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued Geography of the Future As tectonic plates continue to move, Earth’s geography will change dramatically. Scientists predict that in 250 million years, the continents will come together again to form a new supercontinent.

35 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Tectonic Plates

36 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Types of Plate Boundaries

37 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Ridge Push and Slab Pull

38 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 The Supercontinent Cycle

39 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 10 Locations of Earthquakes in South America, 2002-2003

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