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GenreNonfictionComprehension SkillSummarizeText Features LabelsCaptionsDiagramsGlossaryScience ContentEarth’s SurfaceScott Foresman Science 5.9ISBN 0-328-13941-6ì (sk m) bdjebf -Ä-U-Ä-U

Vocabularychemical weatheringcorecrustigneousmantlemechanical weatheringmetamorphicplatesedimentaryWhat did you learn?1. What are the three basic types of rock?2. What are the two kinds of crust onEarth’s surface?3. What is the name of the process thatbreaks down rock by physical forcessuch as ice or gravity?4.byErosionMaryis Millerthe movementof particles away from a place. Write aboutthe various ways that water causes erosion.Include details from the book to supportyour answer.5.Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material.The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).Opener: ML Sinibaldi/Corbis; 6 (TR) Yann Arthus-Bertrand/Corbis, (CR) Brand X Pictures;9 (CR) Roger Ressmeyer/Corbis, (B) Corbis; 10 (TL) ML Sinibaldi/Corbis, (TR, R) Digital Stock;11 Jacques Descloitres/MODIS Rapid Response Team/NASA/GSFC; 12 Joel W. Rogers/Corbis;16 (T) Corbis, (B) Digital Vision; 17 Digital Stock; 18 Digital Vision; 19 (T) Three Lions/Getty Images, (B) Digital Vision.Scott Foresman/Dorling Kindersley would also like to thank: 12 (BR) Natural History Museum, London/DK Images;20 (TR, CL) Natural History Museum, London/DK Images; 21 (CB, BL) Natural History Museum, London/DK Images,(L) National Trust/DK Images.Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson.ISBN: 0-328-13941-6Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America.This publication is protected by Copyright, and permission should be obtained from the publisher prior to anyprohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,mechanical, photocopying, recording, or likewise. For information regarding permission(s), write toPermissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05Summarize Explain how colliding platescan form volcanoes.

The Structure of EarthContinental crustoceanEarth is made up of layers. The layers are called the crust,the mantle, the outer core, and the inner core. Each layer hasdifferent properties.The CrustThe crust is Earth’s top layer. It is also the thinnestlayer. When you stand outside on the ground, you arestanding on Earth’s crust. There are two kinds of crust:continental crust and oceanic crust.Continental crust makes up all of Earth’s land.It can be as thick as seventy-five kilometers. Thethickest continental crust is in mountain areas.Most continental crust is made of granite.Oceanic crust lies beneath most of the oceanfloor. It is made mostly of basalt. This type of rockis dark green or black. The oceanic crust has athickness of about six to eleven kilometers.inner coreouter lopeThe continental crust does not endwhere the ocean begins. It stretches forless than one hundred kilometersinto the water. The underwaterpart of the continental crust isdivided into three sections.The one closest to shoreis the continental shelf.At the edge of the shelf,the continental crustdrops steeply to form thecontinental slope. Thebottom of the slope levelsoff to form the continentalrise. This area is the startingplace of the oceanic crust.land surfaceoceanic crust3

The Mantle and CoreUnderneath Earth’s crust is a layer of nearly solid rockcalled the mantle. It extends from the base of the crustto an average depth of 2,900 kilometers, making up mostof Earth’s material. The top part of the mantle and thecrust above it form the lithosphere.Deep within Earth, the mantle is under very highpressure and heat. The temperature ranges from 360ºC to2,500ºC. Under these extreme temperatures and pressures,the mantle’s rocks do strange things. Even though the rocksare solid, they move and bend like liquid.This rock is always moving. It is moved by convectioncurrents. These currents occur when cool rock sinks andhot rock rises, creating a circular motion. The lithospherefloats on top of the mantle’s convection currents.Convection currentscircular motionof convectioncurrentlower mantleAt the very center of Earth is the core. The distancefrom the surface of Earth to the center of its core is about6,400 kilometers.The core is made of iron and nickel. There is a solidinner core and a liquid outer core. Temperatures at the coreare very hot, reaching 7,000ºC. The liquid in the outer coreis always moving. Its currents make Earth’s magnetic field.Scientists cannot go to the core or mantle to study them.Earth’s layers are so thick thatthey have not even been able todrill through the crust. Scientistshave found other ways to studyEarth’s layers.Sometimes material from themantle pushes up through cracks inEarth’s crust. Scientists can study thismaterial to learn about the mantle.Another way to study Earth’s layersis to measure the vibrations causedby earthquakes with an instrumentcalled a seismograph. Scientistscan also study the mantle inlaboratory experiments.They re-create the heatand pressure of the mantleand then see what theseconditions do to differentkinds of rock.lithosphereseismogramseismograph45

Earthquakesand VolcanoesEarth’s PlatesThe lithosphere covers Earth in a thin layer.This layer is split into sections called plates. Someplates are huge, covering areas larger than continents.The plates float on the molten rock of the mantle.Earth’s plates are slowly moving. Sometimesthe plates grind together, and sometimes the platesmove apart from each other. The places where platesmeet are called plate boundaries. The plates moveless than twenty-five centimeters a year. These smallmovements can cause big changes on Earth’s surface.Some of the changes occur slowly over a longtime. The formation of mountains is a slow change.A change that happens quickly can cause anearthquake. The places where plates meet areoften where earthquakes strike, mountains form,and volcanoes erupt.plateboundaryEarth’s crust isbroken into plates.6The San AndreasFault is a slidingplate boundary.East African Rift ValleyPlates move because convectioncurrents in the mantle push and pullthem in different directions. Gravityalso forces plates to move. Whengravity pulls the edge of a plate downinto the mantle, the rest of the plategets dragged along with it. Thereare three different kinds of plateboundaries: converging, spreading,and sliding.At a converging boundary, twoplates crash into each other. Thiscan push up the edges of the plates,forming a mountain range.A spreading boundary formswhen plates move away from eachother. New crust forms between theplates. The low area between theplates is called a rift valley.An example is the East AfricanRift Valley.At a sliding boundary, two platesmove past each other in oppositedirections. The sliding of the platescan cause cracks in the crust, calledfaults. When the plates rub togetherat a fault, their motion can causeearthquakes. The San Andreas Faultin California has caused manyserious earthquakes.7

epicenterfocusEarthquakesSometimes the forces that change Earth’s surface areconstructive. These forces can build mountains. At othertimes, forces are destructive. Earthquakes and volcanoesare examples of destructive forces.Earthquakes occur at faults. Faults are cracks in Earth’ssurface where the surrounding rock has moved or shifted.Faults can occur anywhere on Earth, but the ones thatcause earthquakes are usually at plate boundaries.When plates slide past one another, they often getstuck together instead of sliding smoothly. Eventuallythe plates unlock and move with a sudden jerk. Thismovement causes the vibrations of an earthquake.Such plate movements happen deep below Earth’ssurface. The place underground where the plates stickand then slip is called a focus. The place on Earth’ssurface above the focus is called the epicenter.8Earthquakes can cause great destruction on Earth’ssurface. Sometimes the side of a hill will slide down andbury an entire neighborhood. This is called a landslide.Many injuries can occur during earthquakes whenbuildings are destroyed. The city of San Franciscowas struck by major earthquakes in 1906 and 1989.The earthquake of 1906 destroyed many more buildingsthan the 1989 earthquake. This is because modernbuildings are designed to flex with an earthquake’smotion, instead of falling down.Earthquakes that occur under the ocean can causetsunamis. These giant waves sometimes cause greatdestruction when theycrash into a coastline.At other times a tsunamiwill go unnoticed.the 1906 San Franciscoearthquakethe 1989 San Francisco earthquake9

Crater Lake in OregonVolcanoesMost volcanoes occur nearconverging plate boundaries. As oneplate moves below another plate, rockpartially melts and makes magma.The magma can be forced throughany weak spots in the crust.Magma that reaches Earth’s surfaceis called lava. The lava flows out ofa hole in the volcano called a vent.The top of a volcano’s main vent iscalled a crater. If a volcano is notactive, the crater can fill with rainwaterand form a lake. For example,Crater Lake in Oregon formed inan inactive volcano. It is the deepestlake in the United States.Gases, such as carbon dioxide andwater vapor, are often mixed with thelava. Trapped gases can blow a holethrough the side of a volcano or pushlava high in the air as it erupts fromthe vent. After the lava erupts from thevolcano, it sometimes cools and turnsinto ash or solid rock before hittingthe ground.Volcanoes sometimes form onthe ocean floor. An island forms whena volcano reaches the water’s surface.The state of Hawaii is a string ofislands that are actually volcanoes.This is a way in which volcanoes areconstructive instead of destructive.Hawaiian Islands1011

How Weathering WorksThere are many ways Earth’s surface can change.Weathering is a slow, destructive process that breaks rocksinto smaller pieces. These pieces are called sediment.Mechanical WeatheringMechanical weathering is the breaking down of rockby physical forces such as gravity, ice, and plant roots. Whenrocks that have been buried come to the surface, the changein pressure can cause cracks in them. Rainwater can moveinto these cracks and freeze. When the rainwater freezes, itexpands and causes the rock to split. This is called ice wedging.The materials in a rock and its environment control therate of weathering. For example, plant roots can grow intocracks in a rock. As the roots grow larger, they can push therock apart. This type of weathering is more likely to occur inwarm, moist climates where plants thrive, rather than in a desert.Plant roots can split soft rocks, such as sandstone, faster thanhard rocks, such as granite.ChemicalWeatheringChemical weathering isthe changing of the materialsin a rock by chemical forces.Raindrops absorb carbondioxide from the air. Thiseroded statuemakes a chemical calledcarbonic acid, which can dissolvesome kinds of rocks. Fungi and other organisms cangive off chemicals that can change some types of rock.Chemical weathering affects some rocks fasterthan others. For example, marble weathers morequickly than slate.Because water is a large part of chemicalweathering, areas with a lot of rain have morechemical weathering than deserts. For example,statues made of limestone in rainy London areoften damaged by acid rain.A tree’s roots can split rock.marble12slate13

SoilSoil is a mix of sediments from different sources.Sediments can come from decayed plant and animal remains.They can also come from bits of weathered rock.The color of soil can range from red to black to gray.Sediments in the soil determine its color. The size of the bitsof sediment determines a soil’s texture and ability to holdwater. Sandy soils have coarse grains. They are rough tothe touch and allow water to pass through easily.Topsoil is the top layerof soil. Because of thehigh amount of decayedmaterials from plants andanimals, plants grow well init. Beneath the topsoil is the topsoilsubsoil. It contains manyminerals but less decayedmatter. Solid bedrock liesbeneath the subsoil.subsoilbedrocksandy soil14Moving SedimentErosion and DepositionErosion is the movement of materials away from one place.Deposition puts sediments in new places. Together, erosion anddeposition work to create sand dunes, valleys, and river deltas.Gravity is the main force that powers erosion. For example,as gravity pulls glaciers down mountains, the rocks underneathare crushed into sediment. The sediment is carried downhillby the glacier. Sharp peaks and jagged ridges are left behindon the mountain.Flowing rivers also cause erosion. As rivers flow downhill,the moving water picks up and carries away bits of sediment.Fast-flowing rivers may erode the land to form deep canyons.Rivers flow more slowly as they near the ocean. Aslow-moving river cannot carry as much sediment. Someof the sediment sinks to the bottom of the river, forminga delta. Deltas, such as the Mississippi Delta in Louisiana,have fertile soil.soil layers15

Wave ErosionOcean storms, tides, and currents erode the shoreline.As waves crash against rocks, the force can break the rocksinto smaller pieces. The sand and gravel in the waves weardown the rock even more. Eventually, these bits of rockare broken down into grains of sand, which can easilybe moved. Waves hit the beach at an angle, pushingthe sand down the coast.Not every part of a shoreline erodes at the same rate.For example, a cave forms when part of a cliff erodesmore quickly than the rest of the cliff.The powerful force of waveserodes rocks and shorelines.Monument Valley in ArizonaWind ErosionWhen strong winds blow sand or dirt against a rock,tiny bits of the rock can break off. These tiny pieces of rockare then carried away by the wind. This form of erosion canmake amazing rock arches and towers. For example, winderosion helped to carve the massive rock formations ofMonument Valley in Arizona.1617

Sand DunesSand dunes are large hills of sand often found in thedesert. These huge features are made by wind erosion.The size and shape of dunes depend on the amount of sand,the number of plants in the area, and the strength of the winds.Winds can also blow sand dunes across the desert. Thewind picks up sand from one side of the dune and depositsthe sand on the other side. When the wind blows in the samedirection most of the time, it can cause the dune to move inthe direction of the wind. For example, dunes in southernEgypt sometimes move twenty to one hundred meters in a year.The side of a sand dune that is away from the wind isalways steeper than the side that faces the wind. Wind pushessand up one side of the dune. After the sand is pushed overthe top of the dune, the wind can no longer reach it. The sandfalls straight down, forming a steep slope.These sand dunes haveformed in the Sahara desert.In the 1930s in theMidwest, overfarmingturned the soil to dust.Field ErosionWind erosion can be a serious problem on farms. If fieldsbecome too dry and there are no plants to hold the soil inplace, wind can blow the topsoil away. This is a problem forfarmers because topsoil is necessary for growing crops.To slow wind erosion, farmers often plant trees alongthe edges of their fields. The trees block some of the windfrom reaching the fields.Trees along the edgeof this field protectthe crops and soilfrom the wind.1819

MineralsRocksScientists can tell minerals apart by theircolor, hardness, and other characteristics.There are three basic types ofrock, each formed in a different way.Igneous RocksMineral propertiesColorMinerals come in all colors from clearto pink, red, blue, green, and black.HardnessHardness is measured onMohs’ scale. Minerals aregraded from one to ten.LusterMinerals can be shiny or dull. Some allowlight through them, but others do not.StreakStreak is the name for the colora mineral leaves behind whenscraped across a tile.Properties of MineralsMinerals are the natural materials that make up rocks.All particles of one mineral are arranged in the same way.Although there are thousands of different minerals, onlya small number make up most of the rocks on Earth.Minerals can be identified by their physical properties.These properties include color, hardness, luster, and streak.20Igneous rocks form whenmelted rock cools and hardens.As the hot, liquid rock cools,mineral crystals form. Meltedrock that cools slowly makesigneous rocks with largecrystals. Rock that coolsquickly forms small crystals.When magma cools slowlyunderground, rocks with largecrystals, such as granite, areformed. Basalt forms when lavais quickly cooled underwater.It has small mineral crystals.The Giant’s Causewayin Ireland is formedfrom basalt.21

Rock cycleSedimentary RocksSedimentary rocks form when layers of mineralsand rock particles harden into solid rock. Sometimesthe particles are cemented together by natural chemicals.The type of sedimentary rock that forms depends onwhat was in the sediment. Some sedimentary rocksare formed from the remainsof animals and plants.Most fossils are found insedimentary rocks. Scientistsstudy the rock surroundingthe fossil to learn more aboutthe environment that existedwhen the organism was living.Metamorphic RocksMetamorphic rocks are formedwhen other rocks are changed by heatand pressure. The mineral crystals inthe rock can change in size or shape.Sometimes the mineral crystals inmetamorphic rock settle in layers.Under high pressure, the rockparticles form rough layers.When the pressure is lower,the layers are fine and thin.This metamorphic rockhas formed in gmetamorphicrockheat andpressureheat andpressurewpo eatrti heng rin, d hering,transporting,depositingtrng, itiin osrpeth deea ng,w tirposanigneousrocksedimentThe Rock Cycletrilobite fossilRocks are constantly being formed, destroyed, or changedfrom one type to another. Pressure, heat, erosion, andweathering help to drive this process, which is called the rockcycle. The rock cycle doesn’t always follow the same order.The Age of Rock LayersThe layers of rock at Earth’s surface are younger thanthe layers of rock underneath, because the lower layers wereformed first. Over time, events such as earthquakes andvolcanoes can cause these layers to shift or even turn over.If the layers are bent or tilted, scientists assume thatsomething happened to move the layers after they weremade. Scientists can tell the ages of fossils by studyingthe layers in which they are found.23

What did you learn?VocabularyGlossarychemical weatheringcorecrustchemicalthe breaking down of rock byigneousweatheringchemical processesmantlemechanical weatheringcoremetamorphic the center part of Earthplatecrustsedimentary the outermost and thinnest layer of Earthigneousrock formed when melted rock coolsand hardensmantlea layer of nearly solid rock betweenEarth’s crust and coremechanicalPictureCreditsweatheringthe breaking down of rock byphysical forcesEvery effort has been made to secure permission and provide appropriate credit for photographic material.The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.metamorphicrock formed when other rocks arechanged by heat and pressurePhoto locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).Opener: ML Sinibaldi/Corbis; 6 (TR) Yann Arthus-Bertrand/Corbis, (CR) Brand X Pictures;9 (CR) Roger Ressmeyer/Corbis, (B) Corbis; 10 (TL) ML Sinibaldi/Corbis, (TR, R) Di

Scott Foresman Science 5.9 Genre Comprehension Skill Text Features Science Content Nonfi

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