Chapter 10 Section 1 Continental Drift Objectives • SummarizeWegener’s hypothesis of continental drift. • Describethe process of sea-floor spreading. • Identifyhow paleomagnetism provides support for the idea of sea-floor spreading. • Explainhow sea-floor spreading provides a mechanism for continental drift.

Chapter 10 Section 1 Continental Drift 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

Chapter 10 Section 1 Continental Drift 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. • Climatic Evidence: changes in climatic patterns suggested the continents had not always been located where they are now.

Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis, continued Similar rock formations and fossil evidence supported Wegener’s hypothesis.

Chapter 10 Section 1 Continental Drift 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.

Chapter 10 Section 1 Continental Drift 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

Chapter 10 Section 1 Continental Drift 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. • The sediment that covers the sea floor is thinner closer to a ridge than it is farther from the ridge • 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.

Chapter 10 Section 1 Continental Drift 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.

Chapter 10 Section 1 Continental Drift 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

Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued As the ocean floor spreads apart, magma rises to fill the rift and then cools to form new rock.

Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued

Chapter 10 Section 1 Continental Drift Paleomagnetism • 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 As magma solidifies to form rock, iron-rich minerals in the magma align with Earth’s magnetic field. When the rock hardens, the magnetic orientation of the minerals becomes permanent.

Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Reversals Scientists have discovered rocks whose magnetic orientations point opposite of Earth’s current magnetic field. • Rocks with magnetic fields that point north (normal polarity) are all classified in the same time periods. • Rocks with magnetic fields that point south (reversed polarity) also all fell into specific time periods

Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Reversals When scientists placed these periods of normal and reversed polarity in chronological order, they discovered a pattern of alternating normal and reversed polarity in the rocks. Scientists used this pattern to create the geomagnetic reversal time scale.

Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Symmetry Scientists discovered a striped magnetic pattern on the ocean floor on each side of a mid-ocean ridge. The pattern on one side of the ridge is a mirror image of the pattern on the other side. When drawn on a map, these patterns match the geomagnetic reversal time scale.

Chapter 10 Section 1 Continental Drift 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.

Chapter 10 Section 1 Continental Drift Wegener Redeemed • Reversal patterns on the sea floor could also be found on land. The reversals in land rocks also matched the geomagnetic reversal time scale. • Because the same pattern appears in rocks of the same ages on both land and the sea floor, scientists agreed that the magnetic patterns showed change over time. • The idea of sea-floor spreading provides a way for the continents to move over the Earth’s surface. • Sea-floor spreading was the mechanism that verified Wegener’s hypothesis of continental drift.

Section 2 The Theory of Plate Tectonics Chapter 10 Objectives • Summarizethe theory of plate tectonics. • Identifyand describe the three types of plate boundaries. • Listand describe three causes of plate movement.

Section 2 The Theory of Plate Tectonics Chapter 10 How Continents Move • plate tectonics the theory that explains how large pieces of the lithospehere, called plates, move and change shape • lithosphere the solid, outer layer of Earth that consists of the crust and the rigid upper part of the mantle • asthenosphere the solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it

Section 2 The Theory of Plate Tectonics Chapter 10 How Continents Move, continued • The lithosphere forms the thinouter shell of Earth and isbroken into several blocks ortectonic plates. • The tectonic plates ride onthe asthenoshpere in much the same way that blocks of wood float on water. • Tectonic plates can include continental crust, oceanic crust, or both. • Continents and oceans are carried along on the moving tectonic plates in the same way that passengersare carried by a bus.

Section 2 The Theory of Plate Tectonics Chapter 10 Tectonic Plates • Scientists have identified about 15 major tectonic plates. • Scientists identify plate boundaries primarily by studying data from earthquakes. • The locations of volcanoes can also help identify the locations of plate boundaries.

Section 2 The Theory of Plate Tectonics Chapter 10 Tectonic Plates, continued The boundaries of tectonic plates do not always match the outlines of continents.

Section 2 The Theory of Plate Tectonics Chapter 10 Types of Plate Boundaries • Tectonic plate boundaries may be in the middle of the ocean floor, around the edges of continents, or even within continents. • The three types of plate boundaries are divergent boundaries, convergent boundaries, and transform boundaries. • Each plate boundary is associated with a characteristic type of geologic activity.

Section 2 The Theory of Plate Tectonics Chapter 10 Types of Plate Boundaries, continued • insert TT

Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion • Many scientists think that the movement of tectonic plates is partly due to convection. • Convection is the movement of heated material due to differences in density that are caused by differences in temperatures.

Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued Mantle Convection • Scientists think that tectonic plates are part of a convection system. • Energy generated by Earth’s core and radioactivity within the mantle heat the mantle. This heated material rises through the cooler, denser material around it.

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.

Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued • Insert TT

Section 3 The Changing Continents Chapter 10 Objectives • Identifyhow movements of tectonic plates change Earth’s surface. • Summarizehow movements of tectonic plates have influenced climates and life on Earth. • Describethe supercontinent cycle.

Section 3 The Changing Continents Chapter 10 Reshaping Earth’s Crust • Slow movements of tectonic plates change the size and shape of the continents over millions of years. • rifting the process by which Earth’s crust breaks apart; can occur within continental crust or oceanic crust

Section 3 The Changing Continents Chapter 10 Reshaping Earth’s Crust, continued • Continents change not only by breaking apart but also by gaining material. • As a plate subducts beneath another plate, islands and other land features on the subducting plate are scraped off the subducting plate and become part of the overriding plate.

Section 3 The Changing Continents Chapter 10 Effects of Continental Change • Modern climates are a result of past movements of tectonic plates. When continents move, the flow of air and moisture around the globe changes and causes climates to change. • Geologic evidence shows that ice once covered most of Earth’s continental surfaces. As continents began to drift around the globe, however, global temperatures changed and much of the ice sheet melted. • As continents rift or as mountains form, populations of organisms are separated. When populations are separated, new species may evolve from existing species.

Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle • supercontinent cycle the process by which supercontinents form and break apart over millions of years • Pangaea the supercontinent that formed 300 million years ago and that began to break up beginning 250 million years ago • Panthalassa the single, large ocean that covered Earth’s surface during the time the supercontinent Pangaea existed

Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued • Using evidence from many scientific fields, scientists can construct a general picture of continental change throughout time. • Several times in the past, the continents were arranged into large landmasses called supercontinents. • Supercontinents broke apart to form smaller continents that moved around the globe. Eventually, the smaller continents joined again to form another supercontinent. • The process by which supercontinents form and break apart over time is called the supercontinent cycle.

Section 3 The Changing Continents Chapter 10 The Supercontinent Cycle, continued

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.

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 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.

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.

Chapter 10 Movements of the Ocean Brain Food Video Quiz

Chapter 10 Standardized Test Prep Multiple Choice • Which of the following factors is most important when determining the type of collision that forms when two lithospheric plates collide? A. the density of each plate B. the size of each plate C. the paleomagnetism of the rock D. the length of the boundary

Chapter 10 Standardized Test Prep Multiple Choice, continued • Which of the following factors is most important when determining the type of collision that forms when two lithospheric plates collide? A. the density of each plate B. the size of each plate C. the paleomagnetism of the rock D. the length of the boundary

Chapter 10 Standardized Test Prep Multiple Choice, continued 2. At locations where sea-floor occurs, rock is moved away from a mid-ocean ridge. What replaces the rock as it moves away? F. molten rock G. older rock H. continental crust I. compacted sediment

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