1 Rocks And 1 Rock And Weathering Weathering

sx05 TE (nc6-4A).fm Page 108 Monday, June 6, 2005 10:44 AMSection11Rocks andWeatheringObjectivesAfter this lesson, students will be able toG.4.1.1 Explain how weathering anderosion affect Earth’s surface.G.4.1.2 Identify what causes mechanicalweathering and chemical weathering.G.4.1.3 Describe the factors that determinehow fast weathering occurs.Rocks and WeatheringReading PreviewKey Concepts How do weathering and erosionaffect Earth’s surface? What are the causes ofmechanical weathering andchemical weathering? What determines how fastweathering occurs?Key TermsTarget Reading SkillRelating Cause and Effect Explain thatcause is the reason for what happens. Theeffect is what happens because of the cause.Relating cause and effect helps studentsrelate the reason for what happens to whathappens as a result.AnswerPossible answers:oxygenwateracid rain weathering erosion uniformitarianism mechanical weathering abrasion ice wedging chemical weathering oxidation permeableTarget Reading SkillRelating Cause and Effect Acause makes something happen. Aneffect is what happens. As you read,identify the causes of chemicalweathering. Write them in a graphicorganizer like the one below.Teaching Resources Transparency G11CausesEffectPreteachBuild BackgroundKnowledgeChemicalweatheringL2Old HeadstonesAsk students whether anyone has seen oldheadstones in a cemetery. Ask: How wouldyou describe the difference between a newheadstone and one that is one hundredyears old? (A typical answer might describethe old headstone as rounded and crumblingwith a faded inscription.) Invite students tospeculate about what processes change aheadstone through the years.L1Skills Focus Drawing conclusionsMaterials 2 fizzing antacid tablets,2 beakers, warm water, plastic stirring rod,plastic bowl, stopwatchTime 10 minutesTips Demonstrate how to grind up a tabletby using the stirring rod in a plastic bowl.Have students use warm water from the108How Fast Can It Fizz?1. Place a fizzing antacid tablet in a small beaker. Then grind upa second tablet and place it in another beaker. The wholetablet is a model of solid rock. The ground-up tablet is amodel of rock fragments.2. Add 100 mL of warm water to the beaker containing the wholetablet. Then stir with a stirring rod until the tablet dissolvescompletely. Use a stopwatch to time how long it takes.3. Add 100 mL of warm water to thebeaker containing the ground-uptablet. Then stir until all of theground-up tablet dissolves. Time howlong it takes.Think It OverDrawing Conclusions Which dissolvedfaster, the whole antacid tablet or theground-up tablet? What variableaffected how long it took each of themto dissolve?Imagine a hike that lasts for months and covers hundreds ofkilometers. Each year, many hikers go on such treks. They hiketrails that run the length of America’s great mountain ranges.For example, the John Muir Trail follows the Sierra Nevadamountains. The Sierras extend about 640 kilometers along theeastern side of California. In the east, the Appalachian Trail follows the Appalachian Mountains. The Appalachians stretchmore than 3,000 kilometers from Alabama to Canada.The two trails cross very different landscapes. The Sierrasare rocky and steep, with many peaks rising 3,000 meters abovesea level. The Appalachians are more rounded and gently sloping, and are covered with soil and plants. The highest peaks inthe Appalachians are less than half the elevation of the highestpeaks in the Sierras. Which mountain range do you think isolder? The Appalachians formed more than 250 million yearsago. The Sierras formed only within the last 10 million years.The forces that wear down rock on Earth’s surface have hadmuch longer to grind down the Appalachians.108 tap. If stopwatches are unavailable, studentscan observe a second hand on a watch orwall clock.Expected Outcome Typical dissolvingtimes are 30 seconds for the whole tabletand 10 seconds for the ground-up tablet.Think It Over The ground-up tabletdissolved faster than the whole tablet.Inferences will vary. Some students mightcorrectly suggest that the ground-up tablethad more surface area exposed to waterthan the whole tablet did and thereforedissolved faster.

sx05 TE (nc6-4A).fm Page 109 Monday, June 6, 2005 10:44 AMWeathering and ErosionThe process of mountain building thrusts rock up to thesurface of Earth. There, the rock is exposed to weathering.Weathering is the process that breaks down rock and othersubstances at Earth’s surface. Heat, cold, water, and ice all contribute to weathering. So do the oxygen and carbon dioxide inthe atmosphere. Repeated freezing and thawing, for example,can crack rock apart into smaller pieces. Rainwater can dissolve minerals that bind rock together. You don’t need to go tothe mountains to see examples of weathering. The forces thatwear down mountains also cause bicycles to rust, paint to peel,sidewalks to crack, and potholes to form.The forces of weathering break rocks into smaller andsmaller pieces. Then the forces of erosion carry the pieces away.Erosion (ee ROH zhun) is the removal of rock particles bywind, water, ice, or gravity. Weathering and erosion worktogether continuously to wear down and carry away therocks at Earth’s surface. The weathering and erosion thatgeologists observe today also shaped Earth’s surface millions ofyears ago. How do geologists know this? Geologists make inferences based on the principle of uniformitarianism (yoon uhfawrm uh TAYR ee un iz um). This principle states that thesame processes that operate today operated in the past.There are two kinds of weathering: mechanical weatheringand chemical weathering. Both types of weathering act slowly,but over time they break down even the biggest, hardest rocks.InstructWeathering andErosionFIGURE 1Effects of WeatheringThe jagged peaks of the SierraNevadas (bottom) formed withinthe last 10 million years. The moregently sloping Appalachians (top)have been exposed to weatheringfor 250 million years.Inferring How can you tell thatthe Sierra Nevadas formed muchmore recently than theAppalachians?What is the difference between weathering anderosion?Teach Key ConceptsL2Effects of WeatheringFocus Remind students that weathering anderosion take place slowly over long periodsof time.Teach Ask: How much longer hasweathering acted on the AppalachianMountains than on the Sierra NevadaMountains? (More than 240 million yearslonger) Do you think that in another240 million years the Sierra NevadaMountains will look like the AppalachianMountains? (Answers will vary. Manystudents will say yes.)Apply Have students give other examples ofweathering and erosion in nature. Examplesinclude the Grand Canyon and many of therock formations that exist in other nationalparks, such as Canyonlands, Bryce Canyon,and Arches. learning modality: logical/mathematicalIndependent PracticeL2Teaching Resources Guided Reading and Study Worksheet:Rocks and WeatheringStudent Edition on Audio CDMonitor Progress 109Differentiated InstructionL1English Learners/BeginningComprehension: Key Concept Explainand clarify the meaning of weatheringby asking students to write the wordweathering in a circle. Then have them listfactors that contribute to weathering (heat,cold, and so on) around the circle as youread through the section. learningmodality: logical/mathematicalEnglish Learners/Intermediate L2Comprehension: Key Concept Studentscan expand on the activity described inBeginning by using the words they havewritten around the circle in a sentence.Students can take cues from the visualsin the text to compose their sentences.learning modality: logical/mathematicalL2Oral Presentation Call on students toclassify examples as either weathering orerosion. Give each student a brief, generaldescription of an example of weathering oran instance of erosion, without usingtechnical terms.AnswersFigure 1 The Appalachians are more worndown than the rugged mountains of theSierra Nevada.Weathering is a process thatbreaks down rock and othermaterials on Earth’s surface, and erosion isthe movement of rock particles by wind,water, ice, or gravity.109

sx05 TE (nc6-4A).fm Page 110 Monday, June 6, 2005 10:44 AMMechanical WeatheringFIGURE 2Teach Key ConceptsMechanical weathering affects all the rock onEarth’s surface.Forming Operational Definitions Study theexamples of mechanical weathering, then write adefinition of each term in your own words.L2Causes of Mechanical WeatheringFocus Point out that all kinds of mechanicalweathering have the same effect: breakingapart rock.Teach Discuss the five types of mechanicalweathering shown in Figure 2, and havevolunteers describe the pictures and typesof weathering in their own words. Ask:In which of the different types is thecomposition of rock different aftermechanical weathering occurs? (None;in each case, the composition of the rockremains the same.)Apply Ask: What are some examples ofeach type of mechanical weathering thatyou have seen? (Students might have seenvery smooth, rounded rocks at a beach, anexample of abrasion; they might have seencracks in sidewalks because of freezing andthawing or plant growth.)Forces of Mechanical WeatheringIceFreezing and ThawingWhen water freezes in a crackin a rock, it expands and makesthe crack bigger. The processof ice wedging also widenscracks in sidewalks and causespotholes in streets.Release of PressureAs erosion removes material from thesurface of a mass of rock, pressure onthe rock is reduced. This release ofpressure causes the outsideof the rock to crackand flake off likethe layers ofan onion.Animal ActionsAnimals that burrowin the ground—including moles,gophers, prairiedogs, and someinsects—loosen andbreak apart rocksin the soil.learning modality: logical/mathematicalTeaching Resources Transparency G12Mechanical WeatheringMechanical WeatheringIf you hit a rock with a hammer, the rock may break intopieces. Like a hammer, some forces of weathering break rockinto pieces. The type of weathering in which rock is physicallybroken into smaller pieces is called mechanical weathering.These smaller pieces of rock have the same composition as therock they came from. If you have seen rocks that are cracked orsplit in layers, then you have seen rocks that are undergoingmechanical weathering. Mechanical weathering works slowly.But over very long periods of time, it does more than weardown rocks. Mechanical weathering eventually wears awaywhole mountains.L1Materials two pieces of sandstone,newspaperTime 5 minutesFocus Tell students that this activity willdemonstrate mechanical weathering.Teach As students watch, have a volunteerrub two pieces of sandstone together over asheet of newspaper. Students will observethat particles fall on the paper.Apply Ask: What kind of mechanicalweathering does this model? (Abrasion)How could such abrasion occur in nature?(Water or wind could carry sand particles intorock, grinding part of it away.) learningmodality: logical/mathematical110110