地理专业外语教案

教案

（2013/2014学年第一学期）

课程名称地理专业外语

课程编号_______101001510

课程性质专业选修课

教学时数__________30__________

教学对象地理科学

授课教师伍铁牛

邵阳学院城市建设系

2013年9月

一、课程教学目的和要求

1、目的：通过本课程的学习，学生可以扩大专业词汇量，提高地理专业英语阅

读、写作、翻译等方面的能力，能初步运用英语与国外学者进行书面的和口头的交

流。使学生在巩固已有专业知识的基础上，掌握科技英语的特点，具备教好的英语

资料查阅及专业英语交流的能力。也就是说，开设本课程，主要是让学生具备“以

英语为工具通过阅读获取专业所需信息的能力”。为本科毕业论文和其他学术论文英

语摘要的写作打好基础。

2、要求：通过《地理专业英语》课程的学习，使学生掌握1000个左右的地理

专业英语词汇；能熟练阅读国外网站和杂志上有关地理科学的文献；能初步读懂地

理科学、地质学等相关学科的英语学术论文；能准确翻译简单的英语文献和中文论

文的英语摘要。

二、课程教学重点和难点

1、重，点、：TheMovementsoftheEarth;LayersoftheEarth;GlobalScaleCirculationofthe

Atmosphere;TheHydrologicCycle;EnvironmentalProtection;NaturalDisasters.

2、难点：AxisTiltandSolarAltitude;CharacteristicsoftheEarth'STerrestrialBiomes;Causes

ofClimateChange;LandformsofGlaciation;AWalterChristaller:HierarchicalPatternsof

Urbanization.

三、教学方法

课程使用传统教学方法授课，教学中采用启发式教学，课堂教学与实验教学相

结合.

四、课时安排

总课时：30课时.

五、考核方式

闭卷考试。

六、参考教材

余中元.地理专业英语.成都：西南交通大学出版社，2008.

目录

Unit1TheEarthandtheUniverse1

Unit2TheMovementsoftheEarth7

Unit3TheStructureoftheEarth15

Unit4SoilsandPlants21

Unit5Weather&Climate27

Unit6WaterontheEarth33

Unit7Geomorphology39

Unit8UrbanPlanning47

Unit9UrbanSpatialStructure53

Unit10Tourism59

Unit11PopulationGeography67

Unit12NaturalResourceUtilization73

Unit13EnvironmentalProtection79

Unit14NaturalDisasters87

Unit15KnowledgeaboutMaps,GISandRS93

Unit1TheEarthandtheUniverse

教研室：地理科学教师姓名：伍铁牛

课程名称地理专业外语授课专业及班次2010级地理科学

授课内容TheEarthandtheUniverse授课方式及学时讲授、2学时

1.Vocabulary：Jupiter,Saturn,Uranus,Neptune,Pluto,comet,asteroid,

meteoroid,electromagnetic,dwarfstar,ProximaCentauri,

2.Sentences：①SolarsystemconsistsofanaveragestarwecalltheSun,the

目的要求

planetsMercury,Mercury,Venus,Earth,Mars,Jupiter,Saturn,Uranusand

Neptune.②TheSunistherichestsourceofelectromagneticenergy(mostlyin

theformofheatandlight)inthesolarsystem.

教学重点：

1.OraldepictingthedifferencebetweenterrestrialplanetsandJovianplanets.

2.Talkingaboutthereasonwhypeopleareinterestedinthemoonexploring.

重点与难点教学难点：

1.Usingoflotsofnewspecializedwords.

2.Oralcommunicationabouttheorbitsandperiodicalsofplanetsinsolar

system.

讲授内容

课文讲解：1学时；

及

时间分配词汇和习题：1学时。

课程使用讲授的方式授课，教学中采用启发式教学，课堂教学与实验教学

教具

相结合。

参考资料余中元.地理专业英语.成都：西南交通大学出版社，2008.

教学内容纲要

TheSolarSystem

OursolarsystemconsistsofanaveragestarwecalltheSun,theplanetsMercury

Venus,Earth,Mars,Jupitei;Saturn,Uranus,andNeptune.Itincludes:thesatellitesof

theplanets;numerouscomets,asteroids,andmeteoroids;andtheinterplanetarymedium.

TheSunistherichestsourceofelcctromawneticenergy(mostlyintheformofheatandlight)

inthesolarsystem.TheSun'snearestknownstellarneighborisareddwarfstarcalled

PruximaCentauri,atadistanceof4.3lightyearsaway.Thewholesolarsystem,together

withthelocalstarsvisibleonaclearnight,orbitsthecenterofourhomegalaxy,aspiraldisk

of200billionstarswecalltheMilkyWay.TheMilkyWayhastwosmallgalaxiesorbitingit

nearby,whicharevisiblefromthesouthernhemisphere.TheyarecalledtheLarqe

MagellanicCloudandtheSmallMaqeHanicCloud.Thenearestlargegalaxyisthe

AndromedaGalaxy.ItisaspiralgalaxyliketheMilkyWaybutis4timesasmassiveandis

2millionlightyearsaway.Ourgalaxy,oneofbillionsofgalaxiesknown,istravelingthrough

intergalacticspace.

Theplanets,mostofthesatellitesoftheplanetsandtheasteroidsrevolvearoundtheSun

inthesamedirection,innearlycircularorbits.WhenlookingdownfromabovetheSun's

northpole,theplanetsorbitinacounter-clockwisedirection.TheplanetsorbittheSuninor

nearthesameplane,calledtheeclirtic.

Plutoisaspecialcaseinthatitsorbitisthemosthighlyinclined(18degrees)andthe

mosthighlyellipticalofalltheplanets.Becauseofthis,forpartofitsorbit,Plutoiscloserto

theSunthanisNeptune.Theaxisofrotationformostoftheplanetsisnearlyperpendicular

totheecliptic.TheexceptionsareUranusandPluto,whicharetippedontheirsides.

CompositionOfTheSolarSystem

TheSuncontains99.85%ofallthematterintheSolarSystem.Theplanets,which

condensedoutofthesamediskofmaterialthatformedtheSun,containonly0.135%ofthe

massofthesolarsystem.Jupitercontainsmorethantwicethematterofalltheotherplanets

combined.Satellitesoftheplanets,comets,asteroids,meteoroids,andtheinterplanetary

mediumconstitutetheremaining0.015%,Thefollowingtableisalistofthemassdistribution

withinourSolarSystem.

Sun:99.85%

Planets:0.135%

Comets:0.01%

Satellites:0.00005%

MinorPlanets:0.0000002%

Meteoroids:0.0000001%

InterplanetaryMedium:0.0000001%

2

TheTerrestrialPlanets

Theterrestrialplanetsarethefourinnermostplanetsinthesolarsystem,Mercury,

Venus,EarthandMars.Theyarecalledterrestrialbecausetheyhaveacompact,rockysurface

liketheEarth's.Theplanets,Venus,Earth,andMarshavesignificantatmosphereswhile

Mercuryhasalmostnone.Thefollowingdiagramshowstheapproximatedistanceofthe

terrestrialplanetstotheSun.

TheJovianPlanets

Jupiter,Saturn,Uranus,andNeptuneareknownastheJovian(Jupiter-like)planets,

becausetheyareallgiganticcomparedwithEarth,andtheyhaveagaseousnaturelike

Jupiter's.TheJovianplanetsarealsoreferredtoasthegasgiants,althoughsomeorallof

themmighthavesmallsolidcores.Thefollowingdiagramshowstheapproximatedistanceof

theJovianplanetstotheSun.

SunandPlanetSummary

ThefollowingtablelistsstatisticalinformationfortheSunandplanets:

DistaRadiusMassRotationMoonsOrbitalOrbitalObliquityDensity

nee(Earth's)(Earth's)(Earth's)InclinationEccentricity(g/cm3)

(AU)

Sun0109332,8025-36*9一一一1.410

0

Mercu0.390.380.0558.8070.20560.1°5.43

ry

Venus0.720.950.8924403.3940.0068177.4°5.25

Earth1.01.001.001.0010.0000.016723.45°5.52

Mars1.50.530.111.02921.8500.093425.19°3.95

Jupiter5.2113180.411161.3080.04833.12°1.33

Saturn9.59950.428182.4880.056026.73°0.69

Uranus19.24170.748150.7740.046197.86°1.29

Neptun30.14170.80281.7740.009729.56°1.64

e

Pluto39.50.180.0020.267117.150.2482119.6°2.03

*TheSun'speriodofrotationatthesurfacevariesfromapproximately25daysattheequatorto36daysat

thepoles.Deepdown,belowtheconvectivezone,everythingappearstorotatewithaperiodof27days.

3

Newwords

Jupitern.木星

Saturnn.土星

Uranusn.天王星

Neptunen.海王星

Pluton.冥王星

cometn.彗星

asteroidn.小行星

meteoroidn.流星体

interplanetarymediumn.行星际物质

electromagneticadj.电磁的

dwarfstarn.矮星

ProximaCentaurin.半人马座的比邻星

theLargeMagellanicCloudn.大麦哲伦星云

TheAndromedaGalaxyn.仙女座星系

intergalacticspacen.，星系际空间

eclipticn.黄道

theJovianPlanetn.类木行星

theTerrestrialPlanetn.类地行星

MilkWayn.银河

counter-clockwisen.逆时针

lightyearn.光年

innermostadj.最里面的

4

教学设计

一、教学步骤:

(1)总体介绍课程性质，总的要求；

(2)概述本次课的主要内容提纲；

(3)逐个教学要点讲解

(4)综合本次内容，提出课后学习要求

二、授课方法

按照重点突出，详略得当，难点详细讲解的原则进行课堂时间分配，掌握太阳系主

要成员的特征以及英语表达方式。

教学方法以讲解和示例为主，联系实际应用，启发学生掌握基本概念。教学手段采

用板书与讲授相结合的方式。在教学中注意到学习对象是高年级本科学生，在前三年的

先行课程里已经系统学习了地理学的主干知识，因此需要在教学中充分挖掘学生的潜

力，发挥学生学习的主观能动性，掌握地理专业外语的基本技能。

5

邵阳学院城市建设系

教案尾页

1＞思考题：

TheexercisesinP7-P9,andReadingMaterial.

I.Vocabulary:

theAndromedaGalaxy,intergalacticspace,ecliptic,theJovianPlanet,MilkWay,counter-clockwise,

lightyear,innermost;

II.Comprehension:

1.RetellthesolarsystemandevolutionstoryoftheEarth.

2.KnowingwellthecompositionoftheUniverse.

2、参考资料：

余中元.地理专业英语.成都：西南交通大学出版社，2008.

3、课后分析：

6

Unit2TheMovementsoftheEarth

教研室：地理科学教师姓名：伍铁牛

课程名称地理专业外语授课专业及班次2010级地理科学

授课内容TheMovementsoftheEarth授课方式及学时讲授、2学时

1.Vocabulary：meansolarday,theNorthPole,earthrevolution,celestial

motion,perihelion,aphelion,tiltoftheEarth'sAxis,perpendicular,summer

solstice,wintersolstice,theautumnalequinox,planeoftheecliptic;

目的要求2.Sentences：①ThetermEarthrotationreferstothespinningoftheEarthon

itsaxis.Onerotationtakesexactlytwenty-fourhoursandiscalledameansolar

day.②Thiscircumstanceisresponsiblefortheannualchangesintheheightof

theSunabovethehorizon.

教学重点：

1.DescribethemechanismoftherevolutionoftheEarth.

2.Describethevariationofdaylengthandthedrivingfactors.

重点与难点教学难点：,'

1.Howdepicttheseasonalchangeandtheearthrevolution.

2.CalculatingtheheightangleoftheSuninlightofdifferentlatitudes.

讲授内容

课文讲解：1学时；

及

时间分配词汇和习题：1学时。

课程使用讲授的方式授课，教学中采用启发式教学，课堂教学与实验教学

教具

相结合

参考资料余中元.地理专业英语.成都：西南交通大学出版社，2008.

教学内容纲要

EarthRotationandRevolution

ThetermEarthrotationreferstothes—iiiningofourplanetonitsaxis.Becauseof

rotation,theEarth'ssurfacemovesattheequatorataspeedofabout467mpersecondor

slightlyover1675kmperhour.IfyoucouldlookdownattheEarth*sNorthPolefromspace

7

youwouldnoticethatthedirectionofrotationiscountec-clockwise(Figure2-1).The

oppositeistrueiftheEarthisviewedfromtheSouthPole.Onerotationtakesexactly

twenty-fourhoursandiscalledameansolarday.TheEarth'srotationisresponsibleforthe

dailycyclesofdayandnight.Atanyonemomentintime,onehalfoftheEarthisinsunlight,

whiletheotherhalfisindarkness.Theedgedividingthedaylightfromnightiscalledthe

circleofillumination.TheEarth'srotationalsocreatestheapparentmovementoftheSun

acrossthehorizon.

South

Figure2-1:ThemovementoftheEarthaboutitsaxisisknownasrotation.Thedirectionof

thismovementvarieswiththeviewer'sposition.FromtheNorthPoletherotationappearsto

moveinacounter-clockwisefashion.LookingdownattheSouthPoletheEarth'srotation

appearsclockwise.

TheorbitoftheEartharoundtheSuniscalledanEarthrevolution.Thiscelestialmotion

takes365.26daystocompleteonecycle.Further,theEarth'sorbitaroundtheSunisnot

circular,butovaloreHiptica](seeFigure2-2).AnellipticalorbitcausestheEarth*sdistance

fromtheSuntovaryoverayear.Yet,thisphenomenonisnotresponsiblefortheEarth's

seasons!ThisvariationinthedistancefromtheSuncausestheamountofsolarradiation

receivedbytheEarthtoannuallyvarybyabout6%.Figure2-2illustratesthepositionsinthe

8

Earth'srevolutionwhereitisclosestandfarthestfromtheSun.OnJanuary3,perihelion,the

EarthisclosesttotheSun(147.3millionkm).TheEarthisfarthestfromtheSunonJuly4,or

aphelion(152.1millionkm).TheaveragedistanceoftheEarthfromtheSunoveraone-year

periodisabout149.6millionkm.

March

Equinox

Mar20/21

June

Solstice

Jun21/22

Aphelion1152,100,000km147,300.000km.Perihelion

July4・i"YJanuary3

TDecember

Solstice

Dec21/22

September

Equinox

Sept22/23

Figure2-2:Positionoftheequinoxes,solstices,aphelion,andperihelionrelativetothe

Earth'sorbitaroundtheSun.

TiltoftheEarth*sAxis

Theeclipticplanecanbedefinedasatwo-dimensionalflatsurfacethat.eometricaHy

intersectstheEarth'sorbitalpatharoundtheSun.Onthisplane,theEarth'saxisisnotatright

anglestothissurface,butinclinedatanangleofabout23.5°fromtheperpendicular.Figure

2-3showsasideviewoftheEarthinitsorbitabouttheSunonfourimportantdates:June

solstice,Septemberequinox,Decembersolstice,andMarchequinox.Notethattheangleof

theEarth'saxisinrelationtotheeclipticplaneandtheNorthStaronthesefourdatesremains

unchanged.Yet,therelativepositionoftheEarth*saxistotheSundoeschangeduringthis

cycle.ThiscircumstanceisresponsiblefortheannualchangesintheheightoftheSunabove

thehorizon.Italsocausestheseasons,bycontrollingtheintensityanddurationofsunlight

receivedbylocationsontheEarth.Figure2-4showsanoverheadviewofthissame

phenomenon.Inthisview,wecanseehowthecircleofilluminationchangesitspositionon

theEarth'ssurface.Duringthetwoequinoxes,thecircleofilluminationcutsthroughthe

9

NorthPoleandtheSouthPole.OntheJunesolstice,thecircleofilluminationistangenttothe

ArcticCircle(66.5°N)andtheregionabovethislatitudereceives24hoursofdaylight.The

ArcticCircleisin24hoursofdarknessduringtheDecembersolstice.

235

Figure2-3:TheEarth'srotationalaxisistilted23.5°fromtheredlinedrawnperpendicularto

theeclipticplane.ThistiltremainsthesameanywherealongtheEarth'sorbitaroundtheSun.

SeasonsareappropriateonlyfortheNorthernHemisphere.

December

Solstice

Dec21/22

Figure2-4:AnnualchangeinthepositionoftheEarthinitsrevolutionaroundtheSun.In

thisgraphic,weareviewingtheEarthfromapositioninspacethatisabovetheNorthPole

(yellowdot)atthesummersolstice,thewintersolstice,andthetwoequinoxc。Notehowthe

positionoftheNorthPoleontheEarth*ssurfacedoesnotchange.However,itsposition

relativetotheSundoeschangeandthisshiftisresponsiblefortheseasons.Theredcircleon

io

eachoftheEarthsrepresentstheArcticCircle(66.5degreesN).DuringtheJunesolstice,the

areaabovetheArcticCircleisexperiencing24hoursofdaylightbecausetheNorthPoleis

tilted23.5degreestowardtheSun.TheArcticCircleexperiences24hoursofnightwhenthe

NorthPoleistilted23.5degreesawayfromtheSunintheDecembersolstice.Duringthetwo

equinoxes,thecircleofilluminationcutsthroughthepolaraxisandalllocationsontheEarth

experience12hoursofdayandnight.SeasonsareappropriateonlyfortheNorthern

Hemisphere.

Figure2-5:DuringtheJunesolsticetheEarth'sNorthPoleistilted23.5degreestowardsthe

Sunrelativetothecircleofillumination.Thisphenomenonkeepsallplacesabovealatitude

of66.5degreesNin24hoursofsunlight,whilelocationsbelowalatitudeof66.5degreesS

areindarkness.TheNorthPoleistilted23.5degreesawayfromtheSunrelativetothecircle

ofilluminationduringtheDecembersolstice.Onthisdate,allplacesabovealatitudeof66.5

degreesNarenowindarkness,whilelocationsbelowalatitudeof66.5degreesSreceive24

hoursofdaylight.

Figure2-6:Duringtheequinoxes,theaxisoftheEarthisnottiltedtowardorawayfrom

theSunandthecircleofilluminatioiicutsthroughthepoles.Thissituationdoesnotsuggest

11

thatthe23.5degreetiltoftheEarthnolongerexists.Thevantagepointofthisgraphicshows

thattheEarth'saxisisinclined23.5degreestowardtheviewerforbothdates(seeFigures2-3

and2-4).TheredcirclesshowninthegraphicaretheArcticCircle.

OnSeptember22or23,alsocalledtheautumnalequinoxintheNorthernHemisphere,

neitherpoleistiltedtowardorawayfromtheSun(Figures2-3,2-4,2-6andseeanimation-

Figure2-9).IntheNorthernHemisphere,March20or21marksthearrivalofthevernal

equinoxorspringwhenonceagainthepolesarenottiltedtowardorawayfromtheSun.Day

lengthsonbothofthesedays,regardlessoflatitude,areexactly12hours.

Newwords

Meansolardayn.平太阳日

Lookdownn.俯视

TheNorthPolen.北极

Earthrevolutionn.地球自转

Celestialmotionn.天体运动

Perihelionn.近日点

Aphelionn.远日点

Summersolsticen.夏至

Wintersolsticen.冬至

Theautumnalequinoxn.秋分

Planeoftheeclipticn.黄道面

12

教学设计

一、教学步骤：

1、回顾上次课内容，课后习题疑难解答

2、概述本次课的主要内容提纲

3、逐个教学要点讲解

4、综合本次内容，提出课后学习要求

二、授课方法

按照重点突出，详略得当，难点详细讲解的原则进行课堂时间分配，掌握地球运动

的特征以及英语表达方式。

教学方法以讲解和示例为主，联系实际应用，启发学生掌握基本概念。教学手段采

用板书与讲授相结合的方式。在教学中注意到学习对象是高年级本科学生，在前三年的

先行课程里已经系统学习了地理学的主干知识，因此需要在教学中充分挖掘学生的潜

力，发挥学生学习的主观能动性，掌握地理专业外语的基本技能。

13

邵阳学院城市建设系

教案尾页

1、思考题：

TheexercisesinP21-P25,andReadingMaterial.

I.Vocabulary:

tiltoftheEarth'sAxis,perpendicular,summersolstice,wintersolstice,theautumnal

equinox,planeoftheecliptic;

ILComprehension:

1.RetellthesolarsystemandevolutionstoryoftheEarth.

2.KnowingwellthecompositionoftheUniverse.

2、参考资料：

余中元.地理专业英语.成都：西南交通大学出版社，2008.

3、课后分析：

14

Unit3TheStructureoftheEarth

教研室：地理科学教师姓名：伍铁牛

课程名称地理专业外语授课专业及班次2010级地理科学

授课内容TheStructureoftheEarth授课方式及学时讲授、2学时

1.Vocabulary：seismic,mantle,crust,basalt,granitic,oceaniccrust,peridotite,

olivine,pyroxene,asthenosphere,lithosphere,mountainbuilding,

2.Sentences：①Thecoreisalayerrichinironandnickelthatiscomposedof

目的要求

twolayers:theinnerandoutercores.②Bothofthesecrusttypesarecomposed

ofnumeroustectonicplatesthatfloatontopofthemantle.Convectioncurrents

withinthemantlecausetheseplatestomoveslowlyacrosstheasthenosphere.

教学重点：

1.GraspthestructureofthelithosphereoftheEarth.

2.RetellthePlatetectonictheoryandfeaturesoftheoceancrustand

重点与难点continentalcrust.

教学难点：

1.Understandingoftheinfluencingfactorsofcontinentalbuildingand

volcanoes.

2.Comparisonandanalysisofthecompositesofthemantleandcrust.

讲授内容

课文讲解：1学时；

及

时间分配词汇和习题：1学时。

课程使用讲授的方式授课，教学中采用启发式教学，课堂教学与实验教学

教具

相结合。

参考资料余中元.地理专业英语.成都：西南交通大学出版社，2008.

教学内容纲要

StructureoftheEarth

TheEarthisanoblatespheroid.Itiscomposedofanumberofdifferentlayersas

determinedbydeepdrillingandseismicevidence(Figure3-1).Theselayersare:

Thecorewhichisapproximately7000kilometersindiameter(3500kilometersinradius)

andislocatedattheEarth'scenter.

15

Figure3-1:LayersbeneaththeEarth'ssurface.

Themantlewhichsurroundsthecoreandhasathicknessof2900kilometers.

Thecrustfloatsontopofthemantle.Itiscomposedofbasaltrichoceaniccrustand

graniticrichcontinentalcrust.

Thecoreisalayerrichinironandnickelthatiscomposedoftwolayers:theinnerand

outercores.Theinnercoreistheorizedtobesolidwithadensityofabout13gramsper

cubiccentimeterandaradiusofabout1220kilometers.Theouterconeisliquidandhasa

densityofabout11gramspercubiccentimeter.Itsurroundstheinnercoreandhasanaverage

thicknessofabout2250kilometers.

Themantleisalmost2900kilometersthickandcomprisesabout83%oftheEarth's

volume.Itiscomposedofseveraldifferentlayers.Theuppermantleexistsfromthebaseof

thecrustdownwardtoadepthofabout670kilometers.ThisregionoftheEarth'sinterioris

thoughttobecomposedofperidotite,anultramaficrockmadeupofthemineralsolivineand

pyroxene.Thetoplayeroftheuppermantle,100to200kilometersbelowsurface,iscalled

theasthenosphere.Scientificstudiessuggestthatthislayerhasphysicalpropertiesthatare

differentfromtherestoftheuppermantle.Therocksinthisupperportionofthemantleare

morerigidandbrittlebecauseofcoolertemperaturesandlowerpressures.Belowtheupper

mantleisthelowermantlethatextendsfrom670to2900kilometersbelowtheEarth*s

surface.Thislayerishotandplastic.Thehigherpressureinthislayercausestheformationof

mineralsthataredifferentfromthoseoftheuppermantle.

Thelithosphereisalayerthatincludesthecrustandtheuppermostportionofthe

mantle(Figure3-2).Thislayerisabout100kilometersthickandhastheabilitytoglideover

therestoftheuppermantle.Becauseofincreasingtemperatureandpressure,deeperportions

ofthelithospherearecapableofplasticflowovergeologictime.Thelithosphereisalsothe

zoneofearthquakes,mountainbuilding,volcanoes,andcontinentaldrift.

Thetopmostpartofthelithosphereconsistsofcrust.Thismaterialiscool,rigid,and

brittle.Twotypesofcrustcanbeidentified:oceaniccrustandcontinentalcrust(Figure3-2).

Bothofthesetypesofcrustarelessdensethantherockfoundintheunderlyinguppermantle

layer.Oceancrustisthinandmeasuresbetween5to10kilometersthick.Itisalsocomposed

ofbasaltandhasadensityofabout3.0gramspercubiccentimeter.

16

Continental

CrustSedimentaryOceanic

DepositsCrust

10km

Lithosphere100km

PlasticAsthenosphere

200km

UpperMantle

(downto670km)

Figure3-2:StructureoftheEarth'scrustandtopmostlayeroftheuppermantle.The

lithosphereconsistsoftheoceaniccrust,continentalcrust,anduppermostmantle.Beneaththe

lithosphereistheasthenosphere.Thislayer,whichisalsopartoftheuppermantle,extendsto

adepthofabout200kilometers.Sedimentarydepositsarecommonlyfoundatthe

boundariesbetweenthecontinentalandoceaniccrust.

Thecontinentalcrustis20to70kilometersthickandcomposedmainlyoflighter

granite(Figure3-2).Thedensityofcontinentalcrustisabout2.7gramspercubiccentimeter.

ItisthinnestinareasliketheRiftValleysofEastAfricaandinanareaknownastheBasin

andRangeProvinceinthewesternUnitedStates(centeredinNevadathisareaisabout1500

kilometerswideandrunsabout4000kilometersNorth/South).Continentalcrustisthickest

beneathmountainrangesandextendsintothemantle.Bothofthesecrusttypesarecomposed

ofnumeroustectonicplatesthatfloatontopofthemantle.Convectioncurrentswithinthe

mantlecausetheseplatestomoveslowlyacrosstheasthenosphere.

MantleMovement

c)

Crust

Figure3-3:TheadditionofglacialiceontheEarth*ssurfacecausesthecrusttodeformand

sink(a).Whentheicemelts,isostaticreboundoccursandthecrustrisestoitsformerposition

beforeglaciation(bandc).Asimilarprocessoccurswithmountainbuildingandmountain

erosion.

OneinterestingpropertyofthecontinentalandoceaniccrustisthatthesetectoOcplates

havetheabilitytoriseandsink.Thisphenomenon,knownasisostacy,occursbecausethe

crustfloatsontopofthemantlelikeicecubesinwater.WhentheEarth*scrustgainsweight

duetomountainbuildingorglaciation,itdeformsandsinksdeeperintothemantle(Figure

17

3-3).Iftheweightisremoved,thecrustbecomesmorebuoyantandfloatshigherin