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Chapter 01
Secondary education (bio sci)
Eastern Visayas State University
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FOCUSomCONCEPTS
HowoldisEarth?
WhatareEarth’sfourmajor“spheres”?
a Whatisthetheoryofplatetectonics?
WhyshouldEarthbethoughtofasasystem?
~ hespectaculareruptionofavolcano,themagnificentsceneryofarockycoast,andthe destructioncreatedbyahurricaneareallsubjectsfortheEarthscientist sciencedealswithmanyfascinatingandpracticalquestionsaboutourenvironment 1 forcesproducemountains?Whyisourdailyweathersovariable?Isclimatereallychanging?How oldisEarth,andhowisitrelatedtotheotherplanetsinthesolarsystem?Whatcausesoceantides? 3 WhatwastheIceAgelike?Willtherebeanother?Canasuccessfulwellbelocatedatthissite? ThesubjectofthistextisEarthscience,becauseourplanet isnotastaticandunchangingmass,itisadynamicbodywithmanyinteractingpartsanda
Toassistyouinlearningtheimportantconceptsinthischapter,focusonthefollowingquestions: ea WhatarethesciencesthatcollectivelymakeupEarthscience? Whataresomeexamplesofinteractionsbetweenpeopleandthenaturalenvironment? Q Howisascientifichypothesisdifferentfromascientifictheory?
on HowdidEarthandotherplanetsinoursolarsystemoriginate?
Whataretheprincipaldivisionsof thesolidEarth?Whatcriteriawereusedtoestablishthesedivisions?
Whatarethemajorfeaturesof thecontinentsandoceanbasins?
What Is Earth Science?
Earthscienceisthenameforallthesciencesthatcollectively seektounderstandEarthanditsneighborsinspace geology,oceanography,meteorology,andastronomy book,UnitsI-4focusonthescienceofgeology,awordthat literallymeans“studyofEarth.”Geologyistraditionallydivided intotwobroadareas:physicalandhistorical. PhysicalgeologyexaminesthematerialscomposingEarthand seekstounderstandthemanyprocessesthatoperatebeneathand uponitssurface,ever-changingplanet forcescreateearthquakes,buildmountains,andproducevolcanic structures,externalprocessesbreakrockapartand sculptabroadarrayoflandforms, wind,andiceresultinagreatdiversityoflandscapes andmineralsforminresponsetoEarth’sinternalandexternal processes,theirinterpretationisbasictoanunderstandingofour planet. Incontrasttophysicalgeology,theaimofhistoricalgeol- ogyistounderstandtheoriginofEarthand thedevelopment oftheplanetthroughits4-billion-yearhistory establishanorderlychronologicalarrangementofthemulti- tudeofphysicalandbiologicalchangesthathaveoccurredin thegeologicpast I).Thestudyofphysicalgeology logicallyprecedesthestudyofEarthhistorybecausewemust
firstunderstandhowEarthworksbeforeweattempttounravel itspast. Unit5, TheGlobalOcean,isdevotedtooceanography. Oceanographyisactuallynotaseparateanddistinctscience. Rather,itinvolvestheapplicationofallsciencesinacompre- hensiveandinterrelatedstudyoftheoceansinalltheiraspects andrelationships,physics, geology,andbiology movementsofseawater,aswellascoastalprocesses,seafloor topography,andmarinelife(Ff? s). Unit6,Earth’sDynamicAtmosphere,examinesthemixtureof gasesthatisheldtotheplanetbygravityandthinsrapidlywith altitude’smotionsand energyfromtheSun,theformlessandinvisibleatmospherereacts byproducinganinfinitevarietyofweather,whichinturncreates thebasicpatternofglobalclimates theatmosphereandtheprocessesthatproduceweatherandcli- mate,meteorologyinvolvestheapplicationof othersciencesinanintegratedstudyofthethinlayerofairthat surroundsEarth. Unit'7,EarthsPlaceintheUniverse,demonstratesthatan understandingofEarthrequiresthatwerelateourplanetto thelargeruniverse objectsinspace,thescienceofastronomy—thestudyofthe universe—isveryusefulinprobingtheoriginsofourown
4 CHAPTER 1 IntroductiontoEarthScience
Earth Science, People,
and the Environment
Theprimaryfocusofthisbookistodevelopanunderstandingof basicEarthscienceprinciples,butalongthewayweexplore numerousimportantrelationshipsbetweenpeopleandthe naturalenvironment bytheEarthsciencesareofpracticalvaluetopeople. NaturalhazardsareapartoflivingonEarth adverselyaffectliterallymillionsofpeopleworldwideandare responsibleforstaggeringdamages andFigure1 processesstudiedbyEarthscientistsarevolcanoes, floods, tsunami,earthquakes,landslides,andhurricanes,these hazardsarenaturalprocesses peopletrytolivewheretheseprocessesoccur. Accordingto theUnitedNations,in2008,forthefirsttime, morepeoplelivedincitiesthaninruralareas towardurbanizationconcentratesmillionsofpeopleintomegac- ities,manyofwhicharevulnerabletonaturalhazards(Figure1). Coastalsitesarebecomingmorevulnerablebecausedevelop- mentoftendestroysnaturaldefensessuchaswetlandsandsand dunes,thereisagrowingthreatassociatedwith
humaninfluencesontheEarthsystemsuchassealevelrisethat islinkedtoglobalclimatechange toseismic(earthquake)andvolcanichazardswhereinappropri- atelanduseandpoorconstructionpractices,coupledwithrapid populationgrowth,areincreasingvulnerability. Resourcesrepresentanotherimportantfocusthatisofgreat practicalvaluetopeople,agreatvari- etyofmetallicandnonmetallicminerals,andenergy(Figure1). Togethertheyformtheveryfoundationofmoderncivilization. Earthsciencedealsnotonlywiththeformationandoccurrence ofthesevitalresourcesbutalsowithmaintainingsuppliesand withtheenvironmentalimpactoftheirextractionanduse. Complicatingallenvironmentalissuesisrapidworldpopu- lationgrowthandeveryone’saspirationtoabetterstandardof living- ingpressureforpeopletodwellinenvironmentshavingsignifi- cantnaturalhazards. NotonlydoEarthprocesseshaveanimpactonpeoplebutwe humanscandramaticallyinfluenceEarthprocessesaswell example,riverfloodingisnatural,butthemagnitudeandfre- quencyoffloodingcanbechangedsignificantlybyhumanactiv- itiessuchasclearingforests,buildingcities,andconstructing dams,naturalsystemsdonotalwaysadjustto
‘TheideaoftheEarthsystemisexploredlaterinthechapter effectsareafocusofChapter20.
FIGURE1 CrystalBeach,Texas,onSeptember16,2008,threedaysafterHurricaneIkecame ashore 165 kilometers(105miles)perhour extraordinarystormsurgecausedmuchofthedamagepicturedhere.(PhotobyEarlNottingham! AssociatedPress)
TheNatureofScientificInquiry 5
is:‘ii ThiscompositenighttimeimageofEarth'scitylightsshowsthegeographicdistributionof settlementsandhelpsusappreciatetheintensityofhumanpresenceinmanypartsoftheplanet.(NASA)
artificialchangesinwaysthatwecananticipate,analter- ationtotheenvironmentthatwasintendedtobenefitsociety oftenhastheoppositeeffect. Atappropriateplacesthroughoutthisbook,youwillhavethe opportunitytoexaminedifferentaspectsofourrelationshipwith thephysicalenviromnent notaddresssomeaspectofnaturalhazards,environmentalissues, orresources knowledgeandprinciplesneededtounderstandenvironmental problems,anumberofthebook’sspecial-interestboxes focusonEarthscience,people,andtheenvironmentbyprovid- ingcasestudiesorhighlightingatopicalissue.
CONCEPTcnncx1.
0 Listatleastfourphenomenathatcanberegardedasnatural hazards.
Windenergyisconsideredarenewableresource useofwindturbinesforgeneratingelectricityisgrowingrapidly. ThesewindturbinesareoperatingnearPalmSprings,California. (PhotobyJohnMead/SciencePhotoLibrary/PhotoResearchers,Inc.) 'OOOO‘OOO-OLOLOOO-O OOOOOOO O OO OOOOOO O O ‘O - -‘='=SE?".-O ..--. .,' I,".-c’4-'7---b--,.'-.-1-Eli.- ' ".** J'.‘3%T'1--.--_____,.....'.nl-1,
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Students SometimesAsk...
Whatisthecurrentworldpopulationandhowfastisit growing? Ittookuntilabouttheyear 1800 fortheworldpopulationto reach 1 billionpeople, thenumberwasabout 4 billion. AccordingtotheU
Bureau,theworldpopulationin mid-2010wasapproaching 6 currentlyaddingpeopleatarate exceeding 75 millionperyear.
The Nature ofScientific
Inquiry
Asmembersofamodernsociety,weareconstantlyremindedof thebenefitsderivedfromscience ofscientificinquiry?Developinganunderstandingofhowscience isdoneandhowscientistsworkisanotherimportantthemethat appearsthroughoutthisbook gatheringdataandsomeoftheingeniousmethodsthathavebeen developedtoovercomethesedifficulties examplesofhowhypothesesareformulatedandtested,aswellas learnabouttheevolutionanddevelopmentofsomemajor scientifictheories. Allscienceisbasedontheassumptionthatthenaturalworld behavesinaconsistentandpredictablemannerthatiscompre- hensiblethroughcareful,systematicstudy scienceistodiscovertheunderlyingpatternsinnatureandthen tousethisknowledgetomakepredictionsaboutwhatshouldor shouldnotbeexpected,givencertainfactsorcircumstances example,byknowinghowoildepositsform,geologistsareable topredictthemostfavorablesitesforexplorationand,perhaps asimportant,howtoavoidregionshavinglittleornopotential. Thedevelopmentofnewscientificknowledgeinvolvessome basiclogicalprocessesthatareuniversallyaccepted- minewhatisoccurringinthenaturalworld,scientistscollect scientific“facts”throughobservationandmeasurement
TheNatureofScientificInquiry 7
investigatorcanformulatemorethanonehypothesistoexplaina givensetofobservations devisemultiplehypotheses,othersinthescientificcommunity willalmostalwaysdevelopalternativeexplanations debatefrequentlyensues, extensiveresearchis conductedbyproponentsofopposinghypotheses,andtheresults aremadeavailabletothewiderscientificcommunityinscientific journals.. Beforeahypothesiscanbecomeanacceptedpartofscientific knowledge,itmustpassobjectivetestingandanalysis- esiscannotbetested,itisnotscientificallyuseful,nomatterhow interestingitmightseem predictionsbemadebasedonthehypothesisbeingconsidered andthatthepredictionsbetestedbycomparingthemagainst objectiveobservationsofnature,hypotheses mustfitobservationsotherthanthoseusedtoformulatethemin thefirstplace- matelydiscarded hypotheses-centeredmodel oftheimiverse—aproposalthatwassupportedbytheapparent dailymotionoftheSun,Moon,andstarsaroundEarth mathematicianJacobBronowskisoablystated,“Scienceisagreat manythings,butintheendtheyallreturntothis:Scienceisthe acceptanceofwhatworksandtherejectionofwhatdoesnot.”
Theory
Whenahypothesishassurvivedextensivescrutinyandwhen competingoneshavebeeneliminated,ahypothesismaybe elevatedtothestatusofascientifictheory wemaysay,“That’sonlyatheory.”Butascientifictheoryisawell- testedandwidelyacceptedviewthatthescientificcommunity agreesbestexplainscertainobservablefacts. Sometheoriesthatareextensivelydocumentedandextremely wellsupportedarecomprehensiveinscope,thethe- cryofplatetectonicsprovidestheframeworkforunderstanding theoriginofmountains,earthquakes,andvolcanicactivity addition,platetectonicsexplainstheevolutionofthecontinents andtheoceanbasinsthroughtime—-ideasthatareexploredin somedetailinlaterchapters.
ScientificMethods
Theprocessjustdescribed,inwhichresearchersgatherfacts throughobservationsandformulatescientifichypothesesand theories,iscalledthescientificmethod, thescientificmethodisnotastandardrecipethatscientistsapply inaroutinemannertounravelthesecretsofournaturalworld. Rather,itisanendeavorthatinvolvescreativityandinsight. RutherfordandAhlgrenputitthisway:“Inventinghypothesesor theoriestoimaginehowtheworldworksandthenfiguringout howtheycanbeputtothetestofrealityisascreativeaswriting poetry,composingmusic,ordesigningskyscrapers.” Thereisnofixedpaththatscientistsalwaysfollowthatleads unerringlytoscientificknowledge,manyscientific
2F,ScienceforAllAmericans(NewYork:Oxford UniversityPress,1990),p.
investigationsinvolvethefollowingsteps:(I)aquestionisraised aboutthenaturalworld;(2)scientificdataarecollectedthatrelate tothequestion(Figure15);(3)questionsareposedthatrelateto thedataandoneormoreworkinghypothesesaredevelopedthat
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8 CHAPTER 1 IntroductiontoEarthScience
mayanswerthesequestions;(4)observationsandexperiments aredevelopedtotestthehypotheses;(5)thehypothesesare accepted,modified,orrejectedbasedonextensivetesting;(6) dataandresultsaresharedwiththescientificcommunityforcri- tiqueandfurthertesting. Otherscientificdiscoveriesmayresultfrompurelytheoretical ideas,whichstanduptoextensiveexamination usehigh-speedcomputerstosimulatewhatishappeninginthe “real”world processesthatoccuronverylongtimescalesortakeplacein extremeorinaccessiblelocations- mentsaremadewhenatotallyunexpectedhappeningoccursdur- inganexperiment pureluck,forasLouisPasteursaid,“Inthefieldofobservation, chancefavorsonlythepreparedmind.” Scientificknowledgeisacquiredthroughseveralavenues,so itmightbebesttodescribethenatureofscientificinquiryasthe methodsofscienceratherthanthescientificmethod, itshouldalwaysberememberedthateventhemostcompelling scientifictheoriesarestillsimplifiedexplanationsofthenatural world. Inthisbook,youwilldiscovertheresultsofcenturiesofsci- entificwork- tions,thousandsofhypotheses,andhundredsoftheories havedistilledallofthistogiveyoua“briefing”onEarthscience. ButrealizethatourknowledgeofEarthischangingdaily,as thousandsofscientistsworldwidemakesatelliteobservations, analyzedrillcoresfromtheseafloor,measureearthquakes, developcomputermodelstopredictclimate,examinethegenetic codesoforganisms,anddiscovernewfactsaboutourplanet's longhistory theories- entificthinkinginyourlifetime.
comcrzrrrcnscx1.
QHowisascientifichypothesisdifferentfromascientific theory? QListthebasicstepsfollowedinmanyscientificinvestigations.
Scales of Space and Time
in Earth Science
WhenwestudyEarth,wemustcontendwithabroadarrayof spaceandtimescales :-11Mi).Somephenomenaarerelatively easyforustoimagine,suchasthesizeanddurationofan afternoonthunderstormorthedimensionsofasanddune phenomenaaresovastorsosmallthattheyaredifficultto imagine(and beyond!)ortheinternalarrangementofatomsinamineralcrystal areexamplesofsuchphenomena. Someoftheeventswestudyoccurinfractionsofasecond. Lightningisanexample tensorhundredsofmillionsofyears- tainsbeganformingnearly 50 millionyearsago,andtheycon- tinuetodeveloptoday.
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it‘-5-;-?;r.‘1;.. Earthscienceinvolvesinvestigationsofphenomenathat rangeinsizefromatomstogalaxiesandbeyond.
Theconceptofgeologictimeisnewtomanynonscientists. Peopleareaccustomedtodealingwithincrementsoftimethat aremeasuredinhours,days,weeks,andyears oftenexamineeventsoverspansofcenturies,butevenacentury isdifficulttoappreciatefully,someoneorsome- thingthatis 90 yearsoldisveryold,andal,000-year-oldartifact isancient. Bycontrast,thosewhostudy Earthsciencemustroutinely dealwithvasttimeperiods—millionsorbillions(thousandsof millions)ofyears’s4- billion-yearhistory,aneventthatoccurred 100 millionyearsago maybecharacterizedas“recent”byageologist,andarocksam- plethathasbeendatedatl0millionyearsmaybecalled“young.”
10 CHAPTER 1 IntroductiontoEarthScience
Accordingtothebigbangtheory,alloftheenergyandmatter oftheuniversewascompressedintoanincomprehensiblyhot anddensestate,ouruniversebegan toexpandandcool,causingthefirstelementsthatformed(hydro- genandhelium)tocondenseintostarsandgalaxies MilkyWayGalaxy 9 billionyearslaterthatplanetEarthandthe restofoursolarsystemtookform. Earthisoneofeightplanetsthat,alongwithmorethan 160 moonsandnumeroussmallerbodies,revolvearoundthe Sun toconcludethatEarthandtheotherplanetsformedatessentially thesametimeandfromthesameprimordialmaterialastheSun. Thenebulartheorystatesthatthebodiesofoursolarsystem evolvedfromanenormousrotatingcloudcalledthesolarnebula (1% 2-t).Besidesthehydrogenandheliumatomsgenerated duringtheBigBang,thesolarnebulaconsistedofmicroscopic dustgrainsandtheejectedmatteroflong-deadstars.(Nuclear fusioninstarsconvertshydrogenandheliumintotheotherele- mentsfoundintheuniverse.) Nearly 5 billionyearsagothishugecloudofgasesand minutegrainsofheavierelementsbegantoslowlycontractdue tothegravitationalinteractionsamongitsparticles(Figure1). Someexternalinfluence,suchasashockwavetravelingfroma catastrophicexplosion(supernova),mayhavetriggeredthecol- lapse,itrotatedfaster
andfasterforthesamereasoniceskatersdowhentheydraw theirarmstowardtheirbodies gravitycameintobalancewiththeoutwardforcecausedbythe rotationalmotionofthenebula(Figure1).Bythistimethe oncevastcloudhadassumedaflatdiskshapewithalargecon- centrationofmaterialatitscentercalledtheprotosun(pre-Sun). (Astronomersarefairlyconfidentthatthenebularcloudformed adiskbecausesimilarstructureshavebeendetectedaround otherstars.) Duringthecollapse,gravitationalenergywasconvertedto thermalenergy(heat),causingthetemperatureoftheinnerpor- tionofthenebulatodramaticallyrise- tures,thedustgrainsbrokeupintomoleculesandextremely energeticatomicparticles,atdistancesbeyondthe orbitofMars,thetemperaturesprobablyremainedquitelow. At—200°C,thetinyparticlesintheouterportionofthenebula werelikelycoveredwithathicklayeroficesmadeoffrozen water,carbondioxide,ammonia,andmethane.(Someofthis materialstillresidesintheoutermostreachesofthesolarsystem inaregioncalledtheOortcloud.)Thedisk-shapedcloudalso containedappreciableamountsofthelightergaseshydrogen andhelium. TheformationoftheSunmarkedtheendoftheperiodof contractionandthustheendofgravitationalheating- aturesintheregionwheretheinnerplanetsnowresidebegan
2:‘.i:Yii1;iisjiFormationofthesolarsystemaccordingtothenebulartheory, whichbeganasacloudofdustandgascalledanebula,startedtogravitationallycollapse contractedintoarotatingdiskthatwasheatedbytheconversionofgravitationalenergyintothermal energy particles-sizeparticlestograduallycoalesceintoasteroid-size bodies.
_ Earth'sSpheres 11
todecline- stanceswithhighmeltingpointstocondenseintotinyparti- clesthatbegantocoalesce(jointogether).Materialssuchas ironandnickelandtheelementsofwhichtherock-forming minerals arecomposed—silicon, calcium,sodium,andso forth—formedmetallicandrockyclumpsthatorbitedtheSun (Figure1).Repeatedcollisionscausedthesemassestocoa- lesceintolargerasteroid-sizebodies,calledplcmetesimals, whichinafewtensofmillionsofyearsaccretedintothefour innerplanetswecallMercury,Venus,Earth,andMars oftheseclumpsofmatterwereincorporatedintotheplanetes- imals arecalledasteroidsandbecome meteoritesiftheyimpact Earth’ssurface. Asmoreandmorematerialwassweptupbythesegrowing planetarybodies,thehigh-velocityimpactofnebulardebris causedtheirtemperaturestorise temperaturesandweakgravitationalfields,theinnerplanets wereunabletoaccumulatemuchofthelightercomponentsof thenebularcloud,hydrogenandhelium, wereeventuallywhiskedfromtheinnersolarsystembythesolar winds. Atthesametimethattheinnerplanetswereforming,the larger,outerplanets(Iupiter,Saturn,Uranus,andNepttme),along withtheirextensivesatellitesystems,werealsodeveloping. BecauseoflowtemperaturesfarfromtheSun,thematerialfrom whichtheseplanetsformedcontainedahighpercentageofices- water,carbondioxide,ammonia,andmethane—aswellasrocky andmetallicdebris forthelargesizeandlowdensityoftheouterplanets mostmassiveplanets,IupiterandSaturn,hadasurfacegravity sufficienttoattractandholdlargequantitiesofeventhelightest elements—hydrogenandhelium.
CONCEPTcnscx1.
QNameandbrieflyoutlinethetheorythatdescribesthe formationofoursolarsystem. QListtheinnerplanetsandtheouterplanets differencesinsizeandcomposition.
Earth's Spheres
Theimagesin areconsideredtobeclassicsbecause they let humanitysee Earth differentlythan ever before. Figurel,knownas“Earthrise,”wastakenwhentheApollo 8 astronautsorbitedtheMoonforthefirsttimeinDecember1968. AsthespacecraftroundedtheMoon,Earthappearedtoriseabove thelunarsurface,referredtoas“TheBlueMarble,”is perhapsthemostwidelyreproducedimageofEarthandwas takeninDecember 1972 bythecrewofApollol 7 duringthelast lunar mission. These early views profoundly altered our conceptualizationsofEarthandremainpowerfulimagesdecades aftertheywerefirstviewed,Earthisbreathtaking initsbeautyandstartlinginitssolitude
oh
B. A,called“Earthrise,"thatgreetedtheApollo 8 astronautsastheirspacecraftemergedfrombehindtheMoon.(NASA Headquarters)B imagecalled“TheBlueMarble"takenfromApollo17- freezonesoverthelandcoincidewithmajordesertregions bandofcloudsacrosscentralAfricaisassociatedwithamuch wetterclimatethatinplacessustainstropicalrainforests blueoftheoceansandtheswirlingcloudpatternsremindusofthe importanceoftheoceansandtheatmosphere,acontinent coveredbyglacialice,isvisibleatthesouthpole.(NASA)
thatourhomeis,afterall,aplanet—small,self-contained,andin somewaysevenfragile,theApollo 8 astronautwho tookthe“Earthrise”photo,expresseditthisway:“Wecameall thiswaytoexploretheMoon,andthemostimportantthingis thatwediscoveredtheEarth.” Aswelookcloselyatourplanetfromspace,itbecomesappar- entthatEarthismuchmorethanrockandsoil,themost conspicuous featuresinFigure l swirlingcloudssuspendedabovethesurfaceofthevastglobal ocean planet. ThecloserviewofEarthfromspaceshowninFigurel helpsusappreciatewhythephysicalenvironmentistradition- allydividedintothreemajorspheres:thewaterportionofour planet,thehydrosphere;Earth’sgaseousenvelope,theatmos- phere;and,ofcourse,thesolidEarth,orgeosphere.
Earth'sSpheres 13
ThisuniqueimageofEarth'satmospheremerging withtheemptinessofspaceresemblesanabstractpainting takenoverwesternChinainJune 2007 byaSpaceShuttlecrew member(callednoctilucentclouds)highin theblueareaareataheightofabout 80 kilometers(50miles).The atmosphereatthisaltitudeisverythin islessthanathousandthofthatatsealevel inthelowerportionoftheimageisthedensestpartoftheatmo- sphere,inalayercalledthetroposphere,thatpractically allweatherandcloudformationoccur's atmosphereoccurswithinjust 16 kilometers(10miles)ofthe surface.(NASA)
distance,whencomparedtothethickness(radius)of thesolidEarth(about6,400kilo-meters,or4,000miles),the atmosphereisaveryshallowlayer- tudeof5(3),and 90 percentoccurswithin just 16 kilometers(10miles)ofEarth’ssurface Despiteitsmodestdimensions,thisthinblanketofairisnev- erthelessanintegralpartoftheplanet notonlyprovidesthe airthatwebreathebutalsoactstoprotectusfromtheSun's dangerousultravioletradiation energy exchanges that continually or 1. /Y ,-6‘ “ Ac 0 ' it x. \ r~._-- :1. ,. es;-» \‘ K I 2 ‘Q 3' K! \ 4 1 l 1 I \ 1
occurbetweentheatmosphereand Earth’ssurfaceandbetweentheatmo- sphereandspaceproducetheeffects wecallweatherandclimate. If, liketheMoon,Earthhad no atmosphere,ourplanetwouldnotonly be lifeless but also many of the processesandinteractionsthatmake thesurfacesuchadynamicplacecould notoperate erosion,thefaceofourplanetmight morecloselyresemblethelunarsurface, whichhasnotchangedappreciablyin nearly 3 billionyears.
Biosphere
ThebiosphereincludesalllifeonEarth. Oceanlifeisconcentratedinthesunlit surfacewatersofthesea :
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Mostlifeonlandisalsoconcentrated nearthesurface,withtreeroots and burrowing animals reaching a few metersundergroundandflyinginsects andbirdsreachingakilometerorso aboveEarth- forms are also adapted to extreme environments. For example, on the oceanfloor,wherepressuresareextreme andnolightpenetrates,thereareplaces wherevents spew hot, mineral-rich fluids that support communities of exoticlife-forms,somebacteria thriveinrocksasdeepas 4 kilometers (2)andinboilinghotsprings. Moreover,aircurrentscancarrymicro- organismsmanykilometersintotheatmosphere weconsidertheseextremes,lifestillmustbethoughtofasbeing confinedtoanarrowbandverynearEarth’ssurface. Plantsandanimalsdependonthephysicalenvironmentfor thebasicsoflife,organismsdomorethanjustrespond totheirphysicalenvironment, life-formshelpmaintainandaltertheirphysicalenvironment. Withoutlife,themakeupandnatureofthegeosphere,hydro- sphere,andatmospherewouldbeverydifferent.
Geosphere
BeneaththeatmosphereandtheoceanisthesolidEarthor geosphere
Thehydrospherecontainsasignificantportionof Earth’sbiosphere examplesandarehometo about 25 percentofallmarinespecies. Becauseofthisdiversity,theyaresometimesreferredtoastheocean equivalentofrainforests.(PhotobyDarrylLeniuk/agefootstock)
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14 i CHAPTER 1 IntroductiontoEarthScience_ _
oftheplanet,adepthof6,400kilometers,makingitbyfarthe largestofEarth’sfourspheres focusesonthemoreaccessiblesurfacefeatures, manyofthesefeaturesrepresenttheoutwardexpressionsofthe dynamicbehaviorofEarth’sinterior prominentsurfacefeaturesandtheirglobalextent,wecanobtain cluestothedynamicprocessesthathaveshapedourplanet. AfirstlookatthestructureofEarth’sinteriorandatthemajor surfacefeaturesofthegeospherecomesinthenextsectionof thischapter. Soil,thethinveneerofmaterialatEarth’ssurfacethatsup- portsthegrowthofplants,maybethoughtofaspartofallfour spheres (geosphere)andorganicmatterfromdecayedplantandanimal life(biosphere).Thedecomposedanddisintegratedrockdebris istheproductofweatheringprocessesthatrequireair(atmos- phere)andwater(hydrosphere).Airandwateralsooccupythe openspacesbetweenthesolidparticles.
CONCEPTcuscx1.
QComparetheheightoftheatmospheretothethicknessof thegeosphere. QHowmuchoftheEarth’ssurfacedooceanscover? QHowmuchoftheplanet'stotalwatersupplydooceans represent? QListandbrieflydefinethefour"spheres"thatconstituteour environment.
A Closer Look at the
Geosphere
Inthissectionwemakeapreliminaryexaminationofthesolid Earth external“anatomy”ofourplanetandbegintounderstandthat thegeosphereistrulydynamic dealasyoubegintodevelopamentalimageofthegeosphere’s internalstructureandmajorsurfacefeatures,sostudythefigures carefully’sinterior—itsstructure andmobility the solidEarth. Althoughportionsofthe surface,such as mountainsandrivervalleys,arefamiliartomostofus,those areasthatareoutofsighton theflooroftheoceanarenotso familiar.
Earth’sInternalStructure
EarlyinEarth’shistorythesortingofmaterialbycompositional (density)differencesresultedintheformationofthreelayers- thecrust,mantle,andcore @n-;- Inadditiontothese compositionallydistinctlayers,Earthisalsodividedintolayers basedonphysicalproperties thesezonesincludewhetherthelayerissolidorliquidandhow
weakorstrongitis toanunderstandingofourplanet.
Earth'sCrust Thecrust,Earth’srelativelythin,rockyouter skin,isoftwodifferenttypes—continentalcrustandoceanic crust“crust,”butthesimilarityendsthere. Theoceaniccrustisroughly 7 kilometers(5miles)thickand composedofthedarkigneousrockbasalt,thecon- tinentalcrustaveragesabout 35 kilometers(22miles)thickbut mayexceed 70 kilometers(40miles)insomemountainous regionssuchastheRockiesandHimalayas crust,whichhasarelativelyhomogeneouschemicalcompo- sition,the continentalcrustconsistsofmanyrocktypes. Althoughtheuppercrusthasanaveragecompositionofa graniticrockcalledgranocliorite,itvariesconsiderablyfrom placetoplace. Continentalrockshaveanaveragedensityofabout2/cm3, andsomehavebeendiscoveredthatare 4 billionyearsold rocksoftheoceaniccrustareyounger(180millionyearsorless) anddenser(about3/cm3)thancontinentalrocks.
Earth’sMantle Morethan 82 percentofEarth’svolumeis containedinthemantle,asolid,rockyshellthatextendstoa depth ofnearly2,900kilometers(1,800miles).Theboundary betweenthecrustandmantlerepresentsamarkedchangein chemicalcomposition mantleispericlotite,whichisricherinthemetalsmagnesium andironthanthemineralsfoundineitherthecontinentalor oceaniccrust. Theuppermantleextendsfromthecrust-mantleboundaryto adepthofabout 660 kilometers(410miles).Theuppermantle canbedividedintotwodifferentparts uppermantleispartofthestifflitbosplzere,andbeneaththatis theweakerasthenosphere. Thelithosphere(sphereofrock)consistsoftheentirecrust anduppermostmantleandformsEarth’srelativelycool,rigid outershell 100 kilometersinthickness,the lithosphereismorethan 250 kilometersthickbelowtheoldest portionsofthecontinents(Figure1).Beneaththisstifflayer toadepthofabout 350 kilometersliesasoft,comparativelyweak layerknownastheasthenosphere(“weaksphere”).Thetop portionoftheasthenospherehasatemperature/pressureregime thatresultsinasmallamountofmelting zonethelithosphereismechanicallydetachedfromthelayer below- pendentlyoftheasthenosphere,afactweconsiderinmore detailinChapter7. ItisimportanttoemphasizethatthestrengthofvariousEarth materialsisafunctionofboththeircompositionandofthetem- peratureandpressureoftheirenvironment theideathattheentirelithospherebehaveslikeabrittlesolid similartorocksfoundon thesurface,therocksofthe lithospheregetprogressivelyhotterandweaker(moreeasily deformed)withincreasingdepth
3“Liquiciwaterhasadensityoflg/cm3;therefore,thedensityofbasaltisthreetimesthat ofwater.
16 CHAPTER 1 IntroductiontoEarthScience
interactalongtheirmargins, I -E,,,,,_.-Sh, r ‘B' calledaconvergentboundary,oneoftheplatesplungesbeneath ff? -.,° --i‘."-.';'*s}. z “TI bl '8'”; F theotheranddescendsintothemantle(Figtire't‘?).Itis ' - '‘\ ir -" ~ ,... '~. Trrmk
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A. Q M ?T.,,,,,,s_.\ onlythoselithosphericplatesthatare cappedwith ’ ‘I “C2’ "‘ illsea \“A “ relativelydenseoceaniccrustthatsinkintothemantle. M; 1.? :(€\L_é -~ x g Anyportionofaplatethatiscappedbycontinental I; i_ 3 onpl‘ ‘~/l/GAfrica _ .\ '7*' ;- crustistoobuoyanttobecarriedintothemantle ii South 4 ’ 1;, ’\ ' result,whentwoplatescarryingcontinentalcrustcon- ‘ America $f;i{1diaz H ‘ 1 q; verge,acollisionofthetwocontinentalmarginsoccurs. ‘i‘"1-sq? }, 1 " . “““1;“/j‘" ..- Theresult1S' theorf maonoti fama'or] mo auntinbe,lt as Kt‘ -;L(7;.Amarcfica Aosrjge-tr if exemplifiedbytheHimalayas. p /£.,,;--r*.’/ Divergentboundariesarelocatedwhereplatespullapart pplg; (Figure1).Herethefracturescreatedastheplatesseparateare filledwithmoltenrockthatwellsupfromthemantle ii‘lGUIiE'i.t’5Earthasitlookedabout 200 millionyearsago materialslowlycoolstoformsolidrock,producingnewsliversof lateTriassicperiod,themoderncontinentsthatweare SeafloonThisprocessOccursalongOceanicridgesWhere,Over fami1' 'th er 'o'nedtofor rcont'nentthatwecall... PangaealaxW1(“allWland").6] 1 maSupe 1 spansofmillionsofyears,hundredsofthousandsofsquarekilo- metersofnewseafloorhavebeengenerated(Figure1).Thus, whilenewseafloorisconstantlybeingaddedattheoceanicridges, C0l1l3il'16I11lfllDrift andPlate T9ClJOI1iCS DuringThepast equalamountsarereturnedtothemantlealongboundaries severaldecadesagreatdealhasbeenlearnedabouttheworkings whoretwoplotosoonvorgo ofourdynamicplanet Atothersites,platesdonotpushtogetherorpullapart. revolutioninourunderstandingofEarth Instead,theyslidepastoneanother,sothatseafloorisneither theearlypartofthetwentiethcenturywiththeradicalproposalOf creatednordestroyed continentaldrift—theideathatthecontinentsmovedaboutthe b()und((.ri9$ faceoftheplanet thatthe Continents andOcean basinsare Permanent and FIGURE'l.'ft8IllustrationshowingsomeofEarth’slithosphericplates. stationaryfeatures onthefaceofEarth reason,thenotionofdriftingcontinentswas it receivedwithgreatskepticismandeven = X ridicule 50 yearspassed !,.-rt"I“No,.th- 1 J beforeenough dataweregathered totransform this controversial Arabia" _ _ /plate hypothesis into a sound theory thatwove together the basic l processesknowntooperateon Plate Earth. The theorythatfinally emerged,calledplatetectonics, providedgeologistswiththefirst S p’ comprehensivemodelofEarth’s Amgfiihan‘,i ‘ Q‘ internalworkings. PPlatei» Euraslan Accordingtothetheoryofplate -,..- ‘plate tectonics,Earth’srigidoutershell (lithosphere)isbrokenintonumerous slabscalledlithosphericplates,which are incontinualmotion. Morethana dozenplatesexist 'fl..‘;l6),Thelargest isthePacificplate,coveringmuchofthePacific Oceanbasin platesincludeanentirecontinentplusalargeareaoftheseafloor. Notealsothatnoneoftheplatesaredefinedentirelybythemargins ofacontinent.
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PlateMotion Drivenbytheunequaldistributionofheatwithin ourplanet,lithosphericplatesmoverelativetoeachotheratavery slowbutcontinuousratethataveragesabout 5 centimeters (2inches)peryear-—aboutasfastasyourfingernailsgrow platesmoveascoherentunitsrelativetoallotherplates,they
TheFaceofEarth 17
'.-mix / e.“§‘§r?’. SOUl|'l _.'-Ll America-.>*.
I—-'- 7
'11='"j¢ji1'f-i','ltit; Convergentboundariesoccurwheretwoplatesmove together,asalongthewesternmarginofSouthAmerica boundariesarelocatedwhereadjacentplatesmoveawayfromone another-Atlanticridgeissuchaboundary.
CONCEPTCHECK1.
0 ListandbrieflydescribeEarth’scompositionallayers. QContrastthelithosphereandtheasthenosphere. QWhatarelithosphericplates?Listthethreetypesofboundaries thatseparateplates.
The Face ofEarth
ThetwoprincipaldivisionsofEarth’ssurfacearethecontinents and theoceanbasins(Fitgiitrue Asignificantdifference betweenthesetwoareasistheirrelativelevels areremarkablyflatfeaturesthathavetheappearanceofplateaus protrudingabovesealevel 0(0),continentslierelativelyclosetosealevel, exceptforlimitedareasofmountainousterrain,the averagedepthoftheoceanfloorisabout3(2) belowsealevel,orabout4(2)lowerthanthe averageelevationofthecontinents. Theelevationdifferencebetweenthecontinentsandocean basinsisprimarilytheresultofdifferencesintheirrespective densitiesandthicknesses about 35 kilometersinthicknessandarecomposedofgranitic rockshavingadensityof about2/cms comprisetheoceaniccrustaverageonly 7 kilometersthickand haveanaveragedensityofabout3/cmg,thethickerand lessdensecontinentalcrustismorebuoyantthantheoceanic crust,continentalcrustfloatsontopofthedeformable rocksofthemantleatahigherlevelthanoceaniccrustforthe samereasonthatalarge,empty(lessdense)cargoshiprides higherthanasmall,loaded(moredense)one.
MajorFeaturesoftheContinents
Thelargestfeaturesofthecontinentscanbegroupedintotwo distinctcategories:extensive,flat,stableareasthathavebeen erodednearlytosealevel,andupliftedregionsofdeformedrocks thatmakeuppresent-daymountainbelts ..
g g- thatyoungmountainbeltstendtobelong, t narrowfeaturesatthemarginsofcontinents, ""A“'Ca andthattheflat,stableareasaretypically . locatedintheinteriorofcontinents. . ._
"v;.=.»-...--‘**-;;;,=-**-=.-. '41“!-1-_ Mountain Belts The most prominent topographicfeaturesofthecontinentsarelinear mountainbelts mountainsappearstoberandom,thisisnotthe case. When the youngest mountains are considered(thoselessthan 100 millionyearsold), wefindthattheyarelocatedprincipallyintwo majorzones-Pacificbelt(theregion surrounding the Pacific Ocean) includes the mountainsofthewesternAmericasandcontinuesintothewestern PacificintheformofvolcanicislandssuchastheAleutians,lapan, andthePhilippines(Figure1). Theothermajormountainousbeltextendseastwardfromthe AlpsthroughIranandtheHimalayasandthendipssouthward intoIndonesia revealsthatmostareplaceswherethicksequencesofrockshave beensqueezedandhighlydeformed,asifplacedinagigantic vise- plesincludetheAppalachiansintheeasternUnitedStatesand theUralsinRussia,the resultofmillionsofyearsoferosion.
i s:r.:;rii-
TheStableInterior Unliketheyoungmountainbelts,which haveformedwithinthelast 100 millionyears,theinteriorsofthe continentshavebeenrelativelystable(undisturbed)forthelast 600 millionyearsorevenlonger,theseregionswere involvedinmountain-buildingepisodesmuchearlierinEarth’s history. Withinthestableinteriorsareareasknownasshields,which areexpansive,flatregionscomposedofdeformedcrystallinerock. NoticeinFigure1 ofthenortheasternpartofNorthAmerica variousshieldshaveshownthattheyaretrulyancientregions containPrecambrian-agerocksthatareover 1 billionyearsold,with somesamplesapproaching 4 billionyearsinage- knownrocksexhibitevidenceofenormousforcesthathavefolded andfaultedthemandalteredthemwithgreatheatandpressure. Thus,weconcludethattheserockswereoncepartofanancient mountainsystemthathassincebeenerodedawaytoproducethese expansive,flatregions. Otherflatareasofthestableinteriorexistinwhichhighly deformedrocks,likethosefoundintheshields,arecoveredbya relativelythinveneerofsedimentaryrocks stableplatforms nearlyhorizontalexceptwheretheyhavebeenwarpedtoform largebasinsordomes stableplatformislocatedbetweentheCanadianShieldandthe RockyMountains(Figure1).
MajorFeaturesoftheOceanBasins
Ifallwaterweredrainedfromtheoceanbasins,agreatvarietyof featureswouldbeseen,includinglinearchainsofvolcanoes,deep canyons,extensiveplateaus,andlargeexpansesofmonotonously
TheFaceofEarth 19
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theUnitedStatesbutrelativelynarrowalongthePacificmar- ginofthecontinent. Theboundarybetweenthecontinentsandthedeep-ocean basinsliesalongthecontinentalslope,whichisarelativelysteep dropoffthatextendsfromtheouteredgeofthecontinentalshelf tothefloorofthedeepocean(Figure1).Usingthisasthe dividingline,wefindthatabout 60 percentofEarth’ssurfaceis representedbyoceanbasinsandtheremaining 40 percentby continents.
Inregionswheretrenchesdonotexist,thesteepcontinental slope merges into a more gradual incline known as the continentalrise- mulationofsedimentsthatmoveddownslopefromtheconti- nentalshelftothedeep-oceanfloor.
Deep-OceanBasins Betweenthecontinentalmarginsand oceanicridgesliethedeep-oceanbasins consistofincrediblyflatfeaturescalledabyssalplains
20 CHAPTER 1 IntroductiontoEarthScience
AppalachianMts. Canadianshield
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ThismapshowsthedistributionofEarth'smountainbelts,stableplatforms,andshields.(PhotobyRobertHildebrand[left];CORBIS [middle];ImageSourcePink/Alamy[right])
flooralsocontainsextremelydeepdepressionsthatareoccasionally morethan 1 1,000meters(36,000feet)deep- oceantrenchesarerelativelynarrowandrepresentonlyasmall fractionoftheoceanfloor,theyareneverthelessverysignificant features thatflankthecontinents,inFigure1-Chile trenchoffthewestcoastofSouthAmericaparallelstheAndes Mountains volcanicislandarcs. Dottingtheoceanflooraresubmergedvolcanicstructures calledseamounts,whichsometimesformlongnarrowchains. Volcanicactivityhasalsoproducedseverallargelavaplateaus, suchasthe OntongIavaPlateaulocatednortheastofNew Guinea,somesubmergedplateausarecomposedof continental-typecrust southeastofNewZealandandtheSeychellesBanknortheastof Madagascar.
OceanicRidges Themostprominentfeatureontheocean flooristheoceanicormid-oceanridge, theMid-AtlanticRidgeandtheEastPacificRisearepartsofthis system windsformorethan70,000kilometers(43,000miles)aroundthe globeinamannersimilartotheseamofabaseball
consistingof highlydeformed rock, such as most ofthe mountainsonthecontinents,theoceanicridgesystemconsists oflayeruponlayerofigneousrockthathasbeenfracturedand uplifted. Understandingthetopographicfeaturesthatcomprisethe faceofEarthiscriticaltoourunderstandingofthemechanisms thathaveshapedourplanet- mousridgesystemthatextendsthroughalltheworld’soceans? Whatistheconnection,ifany,betweenyoung,activemountain beltsanddeep-oceantrenches?Whatforcescrumplerocksto producemajesticmountainranges?Thesearequestionsthatare addressedinsomeofthecomingchaptersasweinvestigatethe dynamicprocessesthatshapedourplanetinthegeologicpast andwillcontinuetoshapeitinthefuture.
CONCEPTcnscrc1.
QDescribethegeneraldistributionofEarth’syoungest mountains. QWhatisthedifferencebetweenshieldsandstable platforms? QWhatarethethreemajorregionsoftheoceanfloorandsome featuresassociatedwitheachregion?
Chapter 01
Course: Secondary education (bio sci)
University: Eastern Visayas State University
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