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How to Use This Presentation • To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” • To advance through the presentation, click the right-arrow key or the space bar. • From the resources slide, click on any resource to see a presentation for that resource. • From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. • You may exit the slide show at any time by pressing the Esc key. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Visual Concepts Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Planet Earth Table of Contents Section 1 Earth’s Interior and Plate Tectonics Section 2 Earthquakes and Volcanoes Section 3 Minerals and Rocks Section 4 Weathering and Erosion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Objectives • Identify Earth’s different geologic layers. • Explain how the presence of magnetic bands on the ocean floor supports the theory of plate tectonics. • Describe the movement of Earth’s lithosphere using the theory of plate tectonics. • Identify the three types of plate boundaries and the principal structures that form at each of these boundaries. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Bellringer A peach can be used as a model for some aspects of Earth’s structure. Compare the drawing of the cross section of the peach below with the cross section of Earth to its right, and answer the following questions. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Bellringer, continued 1. Describe the outer layer of the peach (the skin). What aspect of Earth’s structure does the outer layer of the peach represent? 2. The peach pulp is the next layer. How would you describe it? What aspect of Earth’s structure does the peach pulp represent? 3. The pit is the innermost part of the peach. What is the pit like? What aspect of Earth’s structure does the peach pit represent? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics What is Earth’s Interior Like? • The Earth is made up of three layes: the crust, the mantle and the core. • Crust the thin and solid outermost layer of Earth above the mantle • Mantle the layer of rock between Earth’s crust and core • Core the center part of the Earth below the mantle Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Structure of the Earth Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Formation of Earth’s Crust, Mantle, and Core Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics What is Earth’s Interior Like? continued • Earth’s interior gets warmer with depth. • Geologists believe that the mantle is much hotter than the crust, reaching temperatures higher than 1250° C (2280° F). • The core is hotter than the mantle, reaching temperatures higher than 6000° C (10,800° F). Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Magma Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Magma and Vents Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics What is Earth’s Interior Like? continued • Radioactive elements contribute to Earth’s high internal temperature. • The breakdown of radioactive isotopes uranium, thorium and potassium give off energy that contributes to Earth’s high internal temperatures. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Tectonics • Around 1915, German scientist Alfred Wegener proposed the idea that the continents were once united as a supercontinent and then drifted apart. • He pieced the continents together like a puzzle and called the supercontinent they formed Pangaea. • Wegener found identical fossils on widely separate continents, which supported his idea. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Continental Drift (Pangaea) Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Tectonics, continued • Evidence for Wegener’s ideas came later. • Wegener’s theory of continental drift was ignored until structures discovered on the ocean floor provided evidence for a mechanism for the movement of continents. • Symmetrical bands on either side of a mid-ocean ridge indicate that the two sides of the ridge were moving away from each other and new ocean floor was rising up between them. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Tectonics, continued • Alignment of oceanic rocks supports the theory of moving plates. • Iron in molten rock aligns itself with Earth’s magnetic field as it cools. • The Earth’s magnetic field reverses polarity about every 200,000 years • The process is recorded as magnetic bands in rock, based on the age of the rock. • Symmetrical bands on either side of the Mid Atlantic Ridge suggest that the crust was moving away from the ridge. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Tectonics, continued • Earth has plates that move over the mantle. • The crust and upper portion of the mantle are divided into about seven large pieces called tectonic plates. • Lithosphere the solid, outer layer of Earth, that consists of the crust and the rigid upper mantle Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Tectonics, continued • Plate tectonics the theory that explains how the outer parts of Earth change through time, and that explains the relationships between continental drift, sea-floor spreading, seismic activity, and volcanic activity Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Tectonic Plates Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Tectonics, continued • It is unknown exactly why tectonic plates move. • One hypothesis suggests that plate movement results from convection currents in the asthenosphere, the hot, fluid portion of the mantle. • Another hypothesis suggests that plate movement results from the force of gravity acting on the plates. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Boundaries • Mid-ocean ridges result from divergent boundaries. • The border between two plates is called a boundary. • Divergent boundary a place where two plates are moving apart • New rock forms between divergent boundaries. • Magma liquid rock produced under Earth’s surface Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Divergent and Convergent Boundaries Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Convergent Boundary Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Boundaries, continued • Oceanic plates dive beneath continental plates at convergent boundaries. • Plates slide over each other at a convergent boundary. • Subduction the process by which one lithospheric plate moves beneath another as a result of tectonic forces • The area where one plate slides over another is called a subduction zone. Subduction zones produce ocean trenches, mountains, and volcanoes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Subduction Zone Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Boundaries, continued • Subduction of ocean crust generates volcanoes. • Chains of volcanoes form on the upper plate in a subduction zone. • These volcanoes can form far inland from their associated oceanic trench. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Boundaries, continued • Colliding tectonic plates create mountains. • When two plates collide, mountains are formed at the boundary of the collision. • The Himalayas formed during the collision between the continental tectonic plate containing India and the Eurasian continental plate. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 1 Earth’s Interior and Plate Tectonics Plate Boundaries, continued • Transform fault boundaries can crack Earth. • Plate movement can cause breaks in the lithosphere. • Fault a crack in Earth created when rocks on either side of a break move • Plate movement at transform fault boundaries is one cause of earthquakes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Objectives • Identify the causes of earthquakes. • Distinguish between primary, secondary, and surface waves in earthquakes. • Describe how earthquakes are measured and rated. • Explain how and where volcanoes occur. • Describe the different types of common volcanoes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Bellringer 1. Imagine a corked bottle of soda pop that is standing in a pan of hot water. What do you think will happen as the soda pop heats up? 2. What happens when the pressure builds up in the soda pop? 3. Molten rock in Earth’s mantle is like the soda pop. What happens when pressure builds up in Earth’s mantle? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes What are Earthquakes? • Earthquakes occur at plate boundaries. • Earthquakes are vibrations resulting from rocks sliding past each other at a fault • Seismic waves are waves of energy released during in earthquake • Focus the area along a fault at which the first motion of an earthquake occurs • Epicenter the point on Earth’s surface directly above an earthquake’s focus Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes What are Earthquakes? continued • Energy from earthquakes is transferred by waves. • Earthquakes generate three types of waves: • Longitudinal waves • Transverse waves • Surface waves • Longitudinal waves travel by compressing and stretching crust, also called primary waves (P waves) • Transverse waves travel in an up and downward movement, also called secondary waves (S waves) • Surface waves seismic waves that can move only through solids, move in a rolling circular motion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Longitudinal Waves Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Transverse Wave Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Seismic Waves: Surface Waves Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes What are Earthquakes? continued • Waves move through Earth and along its surface. • Both P waves and S waves spread out from the focus in all directions through the earth. • Surface waves move only on Earth’s surface. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes • Seismologists detect and measure earthquakes. • Seismology the study of earthquakes including their origin, propagation, energy, and prediction • Seismologists use sensitive equipment called seismographs to record data about earthquakes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Seismographs and Mapping Earth’s Layers Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • Three seismograph stations are necessary to locate the epicenter of an earthquake. • There are more than 1000 seismograph stations across the world. • Because P waves travel faster, the difference between the arrival of P waves and the arrival of S waves allows scientists to calculate how far away the focus is. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • Geologists use seismographs to investigate Earth’s interior. • The way P and S waves travel through Earth’s interior help scientists make a model of Earth with layers of different densities. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • The Richter scale is a measure of the magnitude of earthquakes. • Richter scale a scale that expresses the magnitude of an earthquake • The intensity of an earthquake is measured by the modified Mercalli scale. Intensity depends on many factors. • Earthquakes that occur deeper below the Earth’s surface will not be as intense at the surface. • The hardness of the rock above and around an earthquake affects the intensity. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Richter Scale Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • Scientists are trying to predict earthquakes. • Scientists are trying to measure changes in Earth’s crust that might signal an earthquake. • The ability to predict an earthquake could save thousands of lives in the future. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes • A volcano is any opening in Earth’s crust through which magma has reached Earth’s surface. • Vent an opening at the surface of Earth through which volcanic material passes • Volcanoes generally have one central vent, but they can also have several smaller vents. • Magma that reaches Earth’s surface is called lava. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Shield volcanoes have mild eruptions. • Lava from shield volcanoes is very fluid and forms a gently sloping mountain. • Shield volcanoes are some of the largest volcanoes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Composite volcanoes have trapped gas. • Composite volcanoes are made up of alternating layers of ash, cinders, and lava. • The lave is thicker than that of shield volcanoes. • Gases are trapped in the magma, causing eruptions that alternate between flows and explosive activity that produces cinders and ash. • Composite volcanoes are typically tall with steep sides. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Cinder cones are the most abundant volcano. • Cinder cones are the smallest and most common volcanoes. • Large amounts of gas are trapped in the magma, and violent eruptions of hot ash and lava occur. • Cinder cones tend to be active for only a short time and then become dormant. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Types of Volcanoes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Most volcanoes occur at convergent plate boundaries. • 75% of the active volcanoes on Earth are located in an area known as the Ring of Fire. • The Ring of Fire is located along the edges of the Pacific ocean, where oceanic tectonic plates are colliding with continental plates. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Ring of Fire Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Underwater volcanoes occur at divergent plate boundaries. • As plates move apart at divergent boundaries, magma rises to fill the gap. • This magma creates the volcanic mountains that form ocean ridges. • Iceland is a volcanic island on the Mid-Atlantic ridge that is growing outward in opposite directions. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Volcanoes occur at hot spots. • Some volcanoes occur in the middle of plates. • Mantle plumes are mushroom shaped trails of hot rock that rise from deep inside the mantle, melt as they rise, and erupt from volcanoes at hot spots at the surface. • The plumes remain in the same place as the tectonic plate moves, creating a trail of volcanoes. • The Hawaiian Islands are an example of this type of volcanic activity. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Hot Spots and Mantle Plumes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Objectives • Identify the three types of rock. • Explain the properties of each type of rock based on physical and chemical conditions under which the rock formed. • Describe the rock cycle and how rocks change form. • Explain how the relative and absolute ages of rocks are determined. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Bellringer In this section you will be studying rocks and minerals. Rocks are identified by the minerals they contain, the size of their crystals, and other properties. Using the following flowchart, list the properties of the rocks named below. 1. 2. 3. 4. 5. Rock is light colored. go to 2 Rock is dark colored. go to 4 Rock has large crystals. Granite Rock has small crystals. go to 3 Rock is very light and fine grained with a streak of color. Marble Rock is fine grained with definite layers. sandstone Rock has definite small crystals. Basalt Rock has no obvious crystal structure. go to 5 Rock is hard, dark, and glasslike. Obsidian Rock is porous, has air bubbles, and crumbles when rubbed over a hard surface. pumice Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Bellringer, continued Using the flowchart on the previous slide, list the properties of the rocks named below. Granite Basalt Obsidian Sandstone Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks • All rocks are composed of minerals. • There are about 3500 known minerals in Earth’s crust. • Each combination of rock-forming minerals results in a rock with a unique set of properties. • Mineral a natural, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks, continued • Molten rock cools to form igneous rock. • Nearly all igneous rocks are made of crystals of various minerals. • Igneous rock rock that forms with magma cools and solidifies • Extrusive igneous rock cools on Earths surface • Intrusive igneous rock cools while trapped beneath Earth’s surface Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Comparing Intrusive and Extrusive Igneous Rock Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks, continued • Remains of older rocks and organisms form sedimentary rocks. • All rock breaks down over thousands of years. • Weathering the natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose rocks Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks, continued • As pieces of rock accumulate, they can form another type of rock. • Sedimentary rock a rock formed from compressed or cemented layers of sediment • Sediment accumulated pieces of rock and other particles Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks, continued • Loose sediment forms rock in two ways. 1. Layers of sediment get compressed from weight above, forming rock. 2. Minerals dissolved in water seep between bits of sediment and “glue” them together. • Sedimentary rocks are named according to the size of the fragments they contain. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks, continued • Rocks that undergo pressure and heating without melting form metamorphic rock. • Heat and pressure within Earth cause changes in the texture and mineral content of rocks. • Metamorphic rock a rock that forms from other rocks as a result of intense heat, pressure, or chemical processes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Types of Rock Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Structure and Origin of Rocks, continued • Old rocks in the rock cycle form new rocks. • The sequence of events in which rocks can be weathered, melted, altered, and formed is described by the rock cycle. • Rock formation occurs very slowly, often over tens of thousands to millions of years. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks The Rock Cycle Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks How Old Are Rocks? • The relative age of rocks can be determined using the principle of superposition. • The principle of superposition states the following: • Assuming no disturbance in the position of the rock layers, the oldes will be on the bottom, and the youngest will be on top. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks Law of Superposition Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 3 Minerals and Rocks How Old Are Rocks? continued • Radioactive dating can determine a more exact, or absolute, age of rocks. • The radioactive elements that make up minerals in rocks decay over billions of years. • Physicists have determined the rate at which these elements decay. • Geologists can use this data to determine the age of rocks. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Objectives • Distinguish between chemical and physical weathering. • Explain how chemical weathering can form underground caves in limestone. • Describe the importance of water to chemical weathering. • Identify three different physical elements that can cause erosion. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Bellringer 1. What features of a wave allow it to move sand as the wave rolls onto a beach? 2. The Colorado River flows through the Grand Canyon. What do you think made the Grand Canyon? 3. What are some other environmental factors that change the land? 4. How do you think potholes form in a road? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Physical Weathering • There are two types of weathering: physical and chemical. • Physical (or mechanical) weathering breaks rocks into smaller pieces, but does not alter their chemical compositions. • Chemical weathering breaks down rock by changing its chemical composition. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Mechanical Weathering Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Chemical Weathering Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Physical Weathering • Ice can break rocks. • A common kind of mechanical weathering is called frost wedging. • Water seeps into cracks or joints in rock and then freezes. • When water freezes it expands, pushing rock apart. • Every time the ice thaws and refreezes, it wedges farther into the rock. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Physical Weathering, continued • Plants can also break rocks. • The roots of plants can also act as wedges as the roots grow into cracks in the rocks. • As the plant grows, the roots exert constant pressure on the rock, eventually causing pieces to break off. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Chemical Weathering • Some minerals react with oxygen, forming oxides. • Carbon dioxide can cause chemical weathering. • Carbon dioxide can react with water in the air to form carbonic acid. This weak acid reacts with some minerals. • Minerals dissolved by carbonic acid may be washed away, leaving underground pockets, or caves. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Chemical Weathering, continued • Water plays a key role in chemical weathering. • Some minerals react with water, which changes their physical properties. • Some minerals dissolve in water and are carried to new locations. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Chemical Weathering, continued • Acid precipitation can slowly dissolve minerals. • Sulfur dioxide and nitrogen oxides enter the air as a result of burning fossil fuels. • These chemicals can react with water in the air, forming sulfuric acid, nitric acid, or nitrous acid. • When this happens, the precipitation that results is acidic. • Acid Rain Control Program required power plants to reduce the release of sulfur dioxide, which has reduced the acidity of rain. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Acid Precipitation Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion • Erosion a process in which the materials of the Earth’s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravity • Deposition the process in which material such as sediment is laid down, or deposited as a result of erosion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion, continued • Water erosion shapes Earth’s surface. • Water is the most effective physical weathering agent. • Rivers carry sediment to the ocean, and create canyons and riverbeds. • The faster the water flows, the larger the sediment it can carry. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion, continued • Oceans also shape Earth. • Waves crash onto shores, shaping the land. • Ocean waves can create tall cliffs and jagged coastlines. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion, continued • Glaciers erode mountains. • Large masses of ice can exert tremendous forces on rocks. • Glaciers can carve U-shaped valleys in mountains. • Moving glaciers grind rocks below them into fine powder. • Glacial meltwater streams carry the sediment away from the glacier. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion, continued • Wind can also shape the landscape. • Fast moving wind can carry fine sediment. • Sediment carried by wind can smooth Earth’s surface and erode the landscape. • Wind erosion can play a part in forming sandstone arches Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion, continued One theory to explain the formation of arches is shown below. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Erosion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 4 Weathering and Erosion Concept Mapping Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts 1. Which of these occurs where two tectonic plates move away from each other? A. B. C. D. convergent boundary divergent boundary ocean trench subduction zone Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 1. Which of these occurs where two tectonic plates move away from each other? A. B. C. D. convergent boundary divergent boundary ocean trench subduction zone Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 2. What causes earthquakes along the San Andreas fault in California? F. subduction of the Pacific plate by the North American plate G. collision between the Pacific plate and the North American plate H. divergent movement of the Pacific plate and the North American plate I. horizontal movement along the boundary of the Pacific plate and the North American plate Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 2. What causes earthquakes along the San Andreas fault in California? F. subduction of the Pacific plate by the North American plate G. collision between the Pacific plate and the North American plate H. divergent movement of the Pacific plate and the North American plate I. horizontal movement along the boundary of the Pacific plate and the North American plate Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 3. How can the absolute age of a layer of rock be determined? A. by the principle of superposition B. by the ratio of radioisotopes C. by the amount of weathering that has shaped the rock D. by analysis of the types of minerals that make up the rock Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 3. How can the absolute age of a layer of rock be determined? A. by the principle of superposition B. by the ratio of radioisotopes C. by the amount of weathering that has shaped the rock D. by analysis of the types of minerals that make up the rock Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 4. Which of the following is an example of chemical weathering of rock? F. G. H. I. deposition erosion frost wedging leaching Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 4. Which of the following is an example of chemical weathering of rock? F. G. H. I. deposition erosion frost wedging leaching Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 5. Both S waves and P waves travel from the site of an earthquake. How does the difference in the way these waves travel reveal information about the structure of Earth’s interior? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 5. Both S waves and P waves travel from the site of an earthquake. How does the difference in the way these waves travel reveal information about the structure of Earth’s interior? Answer: S waves cannot pass through liquid. The fact that P waves can be detected on the opposite side of the planet, and S waves cannot, indicates a liquid core. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Reading Skills In 1912 Alfred Wegener first proposed the theory that all of the continents formed when one giant continent broke apart. Wegener used the shape of the continents, the distribution of fossils, and similarity of rocks at different parts of the world as evidence. Wegener’s Continental Drift theory was not immediately accepted by scientists. Some wondered about, but could not find, forces that would be strong enough to move such large masses of solid rock over great distances. In the middle of the 20th century, evidence from ocean floor exploration provided new evidence that continents move. The theory of plate tectonics, which explains how land masses move, not across the ocean floor, but across the Earth’s mantle, is now widely accepted. 6. Why do most scientists now accept the idea of moving continents, even though earlier scientists did not? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Reading Skills, continued 6. [See previous slide for question.] Answer: New observations provided evidence that was not available in 1912. These observations explain how continents can move and support the theory. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Interpreting Graphics 7. What type of volcano is illustrated here? A. cinder cone B. composite C. seamount D. shield Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Interpreting Graphics, continued 7. What type of volcano is illustrated here? A. cinder cone B. composite C. seamount D. shield Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.