geology - troop 150troop150minerva.weebly.com/uploads/6/2/0/7/62074623/geology_2005.pdfphysical...

GEoloGY

GeoloGy

Boy SCoUTS oF AMeRICAMeRIT BADGe SeRIeS

Requirements1. Definegeology.Discusshowgeologistslearnaboutrock

formations.Ingeology,explainwhythestudyofthepresentisimportanttounderstandingthepast.

2. PickthreeresourcesthatcanbeextractedorminedfromEarthforcommercialuse.Discusswithyourcounselorhoweachproductisdiscoveredandprocessed.

3. Reviewageologicmapofyourareaoranareaselectedbyyourcounselor,anddiscussthedifferentrocktypesandestimatedagesofrocksrepresented.Determinewhethertherocksarehorizontal,folded,orfaulted,andexplainhowyouarrivedatyourconclusion.

4. DoONEofthefollowing:

a. Withyourparent’sandcounselor’sapproval,visitwithageologist,land-useplanner,orcivilengineer.Discussthisprofessional’sworkandthetoolsrequiredinthislineofwork.Learnaboutaprojectthatthispersonisnowworkingon,andasktoseereportsandmapscreatedforthisproject.Discusswithyourcounselorwhatyouhavelearned.

b. Findoutaboutthreecareeropportunitiesavailableingeology.Pickoneandfindouttheeducation,training,andexperiencerequiredforthisprofession.Discussthiswithyourcounselor,andexplainwhythisprofessionmightinterestyou.

BANG/Brainerd, MN9-2009/057427

5.DoONEofthefollowing(aORbORcORd):

a.SurfaceandSedimentaryProcessesOption

1. Conductanexperimentapprovedbyyourcounselorthatdemonstrateshowsedimentssettlefromsuspen-sioninwater.Explaintoyourcounselorwhattheexerciseshowsandwhyitisimportant.

2. Usingtopographicalmapsprovidedbyyourcoun-selor,plotthestreamgradients(differentelevationsdividedbydistance)forfourdifferentstreamtypes(straight,meandering,dendritic,trellis).Explainwhichonesflowfastestandwhy,andwhichoneswillcarrylargergrainsofsedimentandwhy.

3. Onastreamdiagram,showareaswhereyouwillfindthefollowingfeatures:cutbank,fillbank,pointbar,medialchannelbars,lakedelta.Describetherelativesedimentgrainsizefoundineachfeature.

4. Conductanexperimentapprovedbyyourcounselorthatshowshowsomesedimentarymaterialcarriedbywatermaybetoosmallforyoutoseewithoutamagnifier.

5. Visitanearbystream.Findcluesthatshowthedirectionofwaterflow,evenifthewaterismissing.Recordyourobservationsinanotebook,andsketchthosecluesyouobserve.Discussyourobservationswithyourcounselor.

b.EnergyResourcesOption

1. ListthetopfiveEarthresourcesusedtogenerateelectricityintheUnitedStates.

2. Discusssourcerock,trap,andreservoirrock—thethreecomponentsnecessaryfortheoccurrenceofoilandgasunderground.

3. Explainhoweachofthefollowingitemsisusedinsubsurfaceexplorationtolocateoilorgas:reflectionseismic,electricwelllogs,stratigraphiccorrelation,offshoreplatform,geologicmap,subsurfacestructuremap,subsurfaceisopachmap,andcoresamplesandcuttingsamples.

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4. Usingatleast20datapointsprovidedbyyourcounselor,createasubsurfacestructuremapanduseittoexplainhowsubsurfacegeologymapsareusedtofindoil,gas,orcoalresources.

5. DoONEofthefollowingactivities:

a. Makeadisplayorpresentatonshowinghowoilandgasorcoalisfound,extracted,andprocessed.Youmayusemaps,books,articlesfromperiodicals,andresearchfoundontheInternet(withyourparent’spermission).Sharethedisplaywithyourcounselororasmallgroup(suchasyourclassatschool)inafive-minutepresentation.

b. Withyourparent’sandcounselor’spermissionandassistance,arrangeforavisittoanoperatingdrillingrig.Whilethere,talkwithageologistandasktoseewhatthegeologistdoesonsite.Asktoseecuttingsamplestakenatthesite.

c.MineralResourcesOption

1. Definerock.Discussthethreeclassesofrocksinclud-ingtheiroriginandcharacteristics.

2. Definemineral.Discusstheoriginofmineralsandtheirchemicalcompositionandidentificationproperties,includinghardness,specificgravity,color,streak,cleavage,luster,andcrystalform.

a. Collect10differentrocksorminerals.Recordinanotebookwhereyouobtained(found,bought,traded)eachone.Labeleachspecimen,identifyitsclassandorigin,determineitschemicalcom-position,andlistitsphysicalproperties.Shareyourcollectionwithyourcounselor.

b. Withyourcounselor’sassistance,identify15differentrocksandminerals.Listthenameofeachspecimen,tellwhetheritisarockormineral,andgivethenameofitsclass(ifitisarock)orlistitsidentifyingphysicalproperties(ifitisamineral).

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4. Listthreeofthemostcommonroadbuildingmaterialsusedinyourarea.Explainhoweachmaterialispro-ducedandhoweachisusedinroadbuilding.

5. DoONEofthefollowingactivities:

a. Withyourparent’sandcounselor’sapproval,visitanactiveminingsite,quarry,orsandandgravelpit.Tellyourcounselorwhatyoulearnedabouttheresourcesextractedfromthislocationandhowtheseresourcesareusedbysociety.

b. Withyourcounselor,choosetwoexamplesofrocksandtwoexamplesofminerals.Discusstheminingofthesematerialsanddescribehoweachisusedbysociety.

c. Withyourparent’sandcounselor’sapproval,visittheofficeofacivilengineerandlearnhowgeologyisusedinconstruction.Discusswhatyoulearnedwithyourcounselor.

d. EarthHistoryOption

1. Createachartshowingsuggestedgeologicalerasandperiods.Determineinwhichperiodtherocksinyourregionmighthavebeenformed.

2. Explaintoyourcounselortheprocessesofburialandfossilization,anddiscusstheconceptofextinction.

3. Explaintoyourcounselorhowfossilsprovideinfor-mationaboutancientlife,environment,climate,andgeography.Discussthefollowingtermsandexplainhowanimalsfromeachhabitatobtainfood:benthonic,pelagic,littoral,lacustrine,openmarine,brackish,fluvial,eolian,protectedreef.

4. Collect10differentfossilplantsoranimalsOR(withyourcounselor’sassistance)identify15differentfossilplantsoranimals.Recordinanotebookwhereyouobtained(found,bought,traded)eachone.Classifyeachspecimentothebestofyourability,andexplainhoweachonemighthavesurvivedandobtainedfood.Tellwhatelseyoucanlearnfromthesefossils.

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a. Visitasciencemuseumorthegeologydepartmentofalocaluniversitythathasfossilsondisplay.Withyourparent’sandcounselor’sapproval,beforeyougo,makeanappointmentwithacuratororguidewhocanshowyouhowthefossilsarepreservedandpreparedfordisplay.

b. Visitastructureinyourareathatwasbuiltusingfossiliferousrocks.Determinewhatkindofrockwasusedandtellyourcounselorthekindsoffossilevidenceyoufoundthere.

c. Visitarockoutcropthatcontainsfossils.Determinewhatkindofrockcontainsthefossils,andtellyourcounselorthekindsoffossilevidenceyoufoundattheoutcrop.

d. Prepareadisplayorpresentationonyourstatefossil.Includeanimageofthefossil,theageofthefossil,anditsclassification.Youmayusemaps,books,articlesfromperiodicals,andresearchfoundontheInternet(withyourparent’spermission).Sharethedisplaywithyourcounselororasmallgroup(suchasyourclassatschool).Ifyourstatedoesnothaveastatefossil,youmayselectastatefossilfromaneighboringstate.

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Contents

WhatIsGeology? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

EarthDownUnder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

StreamsCarvingEarth’sSurface . . . . . . . . . . . . . . . . . . . . . 19

EnergyFromOurEarth. . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Minerals:Earth’sTreasures . . . . . . . . . . . . . . . . . . . . . . . . . 59

EarthHistory:TheStoryRocksTell. . . . . . . . . . . . . . . . . . . 77

CareersinGeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

GeologyResources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

The cataclysmic eruption of Washington’s Mount St. Helens in 1980 was a physical process that changed the shape of the mountain. Understanding today’s volcanic eruptions helps us understand eruptions of long ago.

.What Is Geology?

WhatIsGeology?GeologyisthestudyofEarth.ThewordcomesfromtheGreekgeo,meaningearthorland,andlogos,meaningspeechorstory.Themodernstudyofgeologystartedmorethan200yearsago,whenJamesHuttonpublishedTheory of the Earth,claimingthatstudyingthepresentisthekeytounlockingthemysteriesofthepast.ThisprincipleofuniformitarianismstatesthatphysicalprocessesatworktodayonEarth,likewindandwatererosion,havealwaysbeenactiveandareresponsibleforallthefeaturesseenonEarthtoday,includingremnantsfromthedistantpast.

GeologyincludesthestudyofmaterialsthatmakeupEarth,theprocessesthatchangeit,andthehistoryofhowthingshappened,includinghumancivilization,whichdependsonnaturalmaterialsforexistence.

Although much is known about Earth and what it provides humankind, there is much more yet to be discovered—and that is the geologist’s responsibility.

Winds have sculpted this rock formation in eastern Utah.

.earth Down Under

EarthDownUnderEarthisacomplicatedsystemofland,sea,air,plants,andani-malsinconstantchange.Manybranchesofsciencemustcometogetherforgeologiststounderstandwhatfactorshaveshapedtheland,including

• Meteorology,thestudyofweather,toexplaintheworkdonebyrain,streams,oceans,rivers,wind,ice,andfrost

• Geomorphologytostudypresentdayhillsandvalleysandmakeeducatedguessesaboutlandformsthatnolongerexist

• Biologytolearnaboutlivingplantsandanimalsandtheirenvironments

• Paleontologytounlockthesecretsthatfossilsandotherevidencetellaboutthepast

• Chemistryandphysicstounderstandtheformationandcompositionofrocks,minerals,ores,andpetroleum

A Geologist’s ToolsSimplyput,geologistsanswerthequestion,“What’sdownthere?”Theystudyeverythingthatliesbelowthesurfaceoftheground,interpretingthestoryofEarthbystudyingitslayers.

Geological and Topographic MapsWilliamSmith,anEnglishcivilengineer,developedthefirstgeologicalmapintheearly1800s,andthetoolprovedtobesoimportantthatitisstillinusetoday.GeologicalmapsshowwhererocksandsedimentsofthesametypeandageexistonEarth’ssurface.Eachrockorsoiltypeisrepresentedbyadif-ferentcolororlinepattern.Rocksofdifferentformation,butofthesameage,commonlyarerepresentedbydifferentshadesofthesamecolor.

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Because geology

encompasses so

many sciences,

the word geology

sometimes is

replaced with

the phrase earth

sciences.

earth Down Under.

Geologicalmapsareimportantinshowingthedistributionofrocksofthesameageandtype.Forexample,becausediffer-entrocktypeshavedifferentcharacteristicsandcausedifferentconstructionproblems,itisimportantforconstructioncompa-niestoknowthetypeofbedrockbeforeconstructionbegins.Ageologicalmapoftheareawhereconstructionwilltakeplacewillallowtheconstructioncompanytoplanaccordingly.

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Geological Map SymbolsSymbols on a geological map tell the reader clues about what’s under the surface, including underground fault planes, fracture patterns, and dipping formations.

limestone Dolomite Conglomerate Breccia

Sandstone Siltstone Shale Mudstone and clay

Anhydrite Coarse igneous rock

Slate Gneiss and schist

Fine-grained igneous rock

lava flow

.earth Down Under

Geologistscreategeologicalmapsfrominformationgath-eredfromdirectobservationinthefield,interpretationsofaerialphotographs,andsatellitedata.Inadditiontohelpinglocatefaultsandothersurfaceinformation,directfieldobservationsallowgeologiststomeasureseveralsurfaceandsubsurfacefeatures,including

• Attitude,orthedirectiontherockstendtogo

• Strike,orthecompassdirectionofthefeature

• Dip,ortheanglethatthestructuralsurfacemakeswiththegroundsurface;measuredperpendiculartostrike

Ageologistalsoneedsatopographicoverlay(oroverprint)showingwhatison“top”ofthegroundbyindicatingelevationswithcontourlines.Inthesamewaythattheshapeofcontoursonatopographicmapindicatehills,valleys,andstreamdirection,muchcanbetoldaboutasedimentarysequencebytheshapeofitssurfaceexpressions,oroutcrops.Forinstance,curvedoutcropsoftenindicatefolds,orareaswheretherockbedswerebentunderintensepressureintoaseriesoffoldedlayers,likemodelingclay.

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earth Down Under.

Principles of GeologyGeologistshavefoundthatrockandlandformationstendtofollowcertainpatterns.Byapplyingtheprinciplesofsuper-position,stratigraphy,andstructuralgeology,theycanmakebettereducatedguessesontheage,formation,andchangesunderneathEarth’ssurface.

Asrockgrainsdropoutofsuspensioninwater,eitherfromastreamorfromanoceancurrent,theygenerallyaredepositedinlayers,muchlikealayercake:Thebottomlayermustbeputontheplatefirst,followedbythelayersaboveit.Inthesameway,eachlayerofsandormudiscoveredbyanotherlayer,andsoon.Thelaw of superpositionstatesthatyoungerlayersareontopofolderlayers.Youngerlayersmayberemovedorerodedbystreamsorrivers,andthenevenyoungerlayersmaybeaddedontop.

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Horizontal layers

.earth Down Under

Sometimesrocksshowabreakinthesequenceofthelay-ers.Theseunconformitiescanbecausedbyerosionorpressure.Abruptchangesthatcutacrossaseriesofrocklayersgenerallyindicatefaults,orareaswheretherocklayerswerebrokenandwheretherocksononesideofthebreakmoveawayfromtherocksontheotherside.

Thesethreeconcepts—superposition(youngerlayersontop),stratigraphy(howlayersform),andstructuralgeology(howlayerschangeasinfolding)—combinetohelpgeolo-gistsfigureoutwhat’sbeneathEarthusinginformationaboutEarth’ssurface.

Stratigraphy is

the study of

Earth’s layers and

how they formed.

The study of how

rocks are folded

and broken, or

faulted, is called

structural geology.

Try this. Fill a jar half full with gravel, rocks, sand and soil. Finish filling the jar with water. Close the lid and shake vigorously. Let it stand still for a few hours. Did lay-ers form? Make a soil chart of the layers. Why did the largest grains settle on the bottom first?

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Faults

earth Down Under.

other ToolsAlthoughgeologicalmapsareveryimportant,theyhelpageologistreadandinterpretonlywhatisonEarth’ssurface.Geologistshavemanyothertoolsandsourcesofinformation.Anexampleiswell information.Youmightthinkofwellsaspipesthatbringwaterorpetroleumtothesurface,buttheyalsocangiveusmuchinformationaboutEarth’ssubsur-face,includinginformationaboutthesequenceofbedsandstructuralfeaturesmanythousandsoffeetbelowthesurface.Measurementsmadeinwells,usingelectricalgraphs,orwell logs,andactualrocksampleslikecoresandcuttingsretrievedduringdrilling,preciselyshowtherocksinthatlocation.

Oneofthemostcommontoolsintheoilindustryis reflec-tion seismology,inwhichsoundwavesaresentintoEarthtomeasurethereflections,orechoes,tothetopsofvariousrocklayers.Seismicreflectionsgiveanindirectmeasureofsub-surfacerocksandgivegeologistscluesastowhatliesunderEarth’ssurface.

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Geologists use

wells, or bore

holes, to gain

information in the

subsurface for

mining, engineer-

ing, and many

other purposes.

Seismic trucks generate energy waves into earth to help scien-tists record reflections against the different rock layers.

.earth Down Under

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This illustration was created from seismic reflection information collected by recording the timing and reflection angles of energy waves generated by seismic trucks. The darker waves and lines are representative of the rock formations under earth’s surface.

.Streams Carving earth’s Surface

StreamsCarvingEarth’sSurfaceGeologistsstudyrockstolearnthehistoryoftheirformation.Riversandstreamscarrysmallpiecesofrock,calledsediment,intheircurrent,andthosepiecessettlewhenthecurrentlosesitsenergy.

Sedimentary Rock Sedimentary(sed-uh-MEN-tar-ee)rockisformedfrompiecesofweatheredorbrokendownrocksthatarecarriedanddepositedbyforceslikewater,wind,orglaciersandthencompressedinlayers.Understandingwheretherockgrainscomefromandhowtheybecomesortedintolayersintheirpresentlocationandthicknesscanleadgeologiststowater,oil,andnaturalgas.

Sedimentarygeologistsstudyhowmovingwatererodesrockgrainsfromtheiroriginalposition,sortsthembysize,andredepositsthemintotheirnewlocation.Afterdepositioninthisnewlocation,otherprocessescementthegrainstogetherintorockunits.

Becauseroundgrainsdonotfitperfectlytogetherwhenpackedintovolume,therearespacesbetweenthegrains(pores)wherewater,oil,naturalgas,orotherfluidscancollect.Thenewrockislikeagiantsponge.Althoughitlookssolid,itcanholdalotoffluidinitspores.

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Sedimentary

rocks are the

most common

rock formations

on the continental

surface.

Streams Carving earth’s Surface.

Sediments in SuspensionTheforceofwatercurrentprovidestheenergytoholdparticlesofdirtandrockinsuspension,fromthepointwheretheywashintothestreamuntiltheysettletothebottom.Theamountofstreamenergydetermineshowbigagraincanbetransported.Biggergrainsrequiremoreenergy,orfasterstreamflow.Steamenergyalsodetermineswherethegrainisdropped,ordeposited.Whenasteamslowsdown,itlosesenergy,andthebiggerorheaviergrainsaredropped.

Theshapeofastream’spath,oritsmorphology,affectsthestreamenergy.Everywindingstreamhasplaceswherethecurrentisfasterorslower.Geologistsstudythepatternoffluidflowtohelpdeterminetheflowpatterninancientstreamsnowrepresentedbyrockformations.

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There is not a

corner of North

America that

does not have

a streambed for

Scouts to study.

The 1848 California Gold Rush. Only a few prospec-tors struck it rich in California. Some of them were lucky, but the smartest prospectors knew where to pan for gold in a stream, because they knew where gold accumulated. The tiny yellow flakes of gold were heavy for their small size. In fact, a volume of gold weighs 19 times more than the same volume of water. For this reason, gold settles to the bottom of a stream quickly as the current loses speed. The successful prospector knew these things, which geologists know today.

Physicist Albert Einstein studied the pattern of fluid flow by watching the opposing directions of swirling tea leaves in his teacup.

Stream Gradient Astream’senergyisdeterminedbythespeedofthewaterflow.Streamshaveahigheroverallenergyinthesectionswithasteepergradientordownhillslope.Waterrushingfromhigherelevationtolowerelevationisneverstopped,butitcanbesloweddownbylocalrockformationsorbytrapsanddams.Rememberthatfast-movingwatertransportslargerandheaviergrainswhileslower-movingwaterbeginstodropthelargerandheaviergrains.

Onewaytoestimatehowfastwaterwillflowistocalcu-latethestream gradient,ortheratioofverticalversushorizon-taldistance,inequalunits.Inotherwords,iftheelevationofastreamdrops10feetforevery100feetthatitflows,yousaythatthegradientis10to100(or1to10).Astreamwiththishighgradientwillhaveagreatdealofenergyinitswaterflow.Aslowstreammightbeonethatflows10miles(or52,800feet)foreverydropof10feet.Inthiscase,theratiowillbe10feetto52,800feet(or1to5,280).Thiswouldbealowgradi-entrepresentinglowenergyandaslow-movingstream.

To calculate

steam gradient,

you must first

convert any

measurements

that are in miles

to feet. To do that,

simply multiply

the number of

miles by 5,280.

(There are 5,280

feet in a mile.)

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Stream

100 Feet DiStance10 Feet elevation

Activity 1. How Do Sediments Settle From Suspension?Youhavelearnedthatsedimentsarecarriedbyrivercurrentanddepositeddownstream.Inthisexperimentyouwilllearnhowsedimentsize,rivergradient,andobstaclesaffectsuspension.

PRoCeDUReSStep 1—Createamountainslopefromapieceofplywoodoracardboardbox(evenapizzabox)reinforcedwithayardstick.Coverthecardboardwithaplasticgarbagebag.Withanadult’shelp,sprayfoaminsulationonthemoun-tainslopetomakeanS-shapedfurrowforarivertoflowthrough.

Step 2—Whenthefoamhasdried,elevateoneendofthemountainslopeononebrick.Youmayallowtheotherendtorestonaconcretesurfacelikeadriveway.

Step 3—Mix1teaspoonofsand,1teaspoonofdirt,and2teaspoonsofgravelinapproximately2cupsofwater.Stir.Noticeifthesand,dirt,androcksaresuspendedinthewater.

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Step 4—Pourthemixtureintothefurrowatthehighendofyourmountainside.Recordyourobservations.

Step 5—Raisetheupperendofthemountainbyaddingasecondbrick,thenrepeatsteps3and4.

Step 6—Elevatetheupperendofthemountainfourtoeighttimeshigherbyaddingmorebricksorothersupport,thenrepeatsteps3and4.

oBSeRvATionS1.Whenyoustirredthesand,dirt,andgravelinthewater,did

theybecomesuspended?Whatsettledfirstafteryoustoppedstirring?Whatdoyouthinkwouldsettlefirstinastreambed?

2.Whenyoupouredthemixturedownthemountainslope,didthesand,gravel,ordirtsettleoutfirst?

3.Whereonthemountainsidedidthesandtendtosettle,onthepointbarorthecutbank?Wheredidthegraveltendtosettle?Wheredidthedirttendtosettle?

4.Astheinclineincreasedandthemountaingrewhigher,whathappenedtotheamountofsedimentthatsettledonthemountainside?

ConClUSionSWhensearchingforsomethinginariver,beitoilinanancientriverthatflowedyearsago,goldforthegoldrushprospector,oradroppedScoutcompassinastream,itishelpfultoknowwhereheavieritemssettlewhenflowingdownstream.Largerheaviermaterialslikerockssettleoutfirst.Thefasterthestreamflows,thelessthesuspendedsolidssettleout.Thestreammovesmoreslowlywhenthemountainsideisnotashigh.Sedimentofallsizeswillsettleoutwhentheyslowdowngoingaroundapointbar.Onlytheheaviestrockswillsettleoutinacutbankarea.Thesesameprinciplesapplywhetherinaragingriver,agurglingbrook,orastraightortwistingstream.

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See “Stream

Landforms” later

in this chapter for

more information

about cut bank

and point bar.

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GlaciersTo understand the glaciers of the Ice Age, geologists study today’s remnant glaciers, called mountain glaciers, and continental ice sheets. Mountain glaciers still can be found in Glacier National Park in Montana and in Alaska. Continental ice sheets still exist in Greenland and Antarctica.

Throughout geologic time, glaciers have shaped Earth’s surface. Many sci-entists believe that massive ice sheets like those that cover Antarctica today once covered the north half of Eurasia and from the North Pole to what is now Kansas and Illinois. Because these gla-cial sheets were so thick—nearly a mile in some places—and may have taken thousands of years to melt, entire rivers flowed around them. When the conti-nental ice sheets finally finished melting, the glaciers had carved out the channels of today’s major river systems through Canada and the United States. Most geologists believe that glaciers weighing trillions of tons dug out the low spots that became the Great Lakes.

Mountain glaciers exist only in a single mountain valley. Today’s mountains show evidence of long-gone mountain glaciers. Have you ever hiked the high country and noticed wide, U-shaped mountain val-ley walls (compared with narrow, sharply pointed V-shaped valleys). To form a U-shaped valley, a single river of ice flowed through and cut away the sides and bottom of the valley, creating its wider appearance.

Glaciers also scrape up huge amounts of rock and dirt and, as the ice melts, deposit this material. Large deposits of glacial sediment, or till, and glacially derived wind-blown deposits called loess can be seen today. These till deposits form into mounds and piles called moraines and stringlike, low-profile valley ridges called eskers.

Stream PatternsTheshapeofastreamchannel,orshapeofthestreamflow,alsocandeterminethestrengthofastream’senergy.Ageolo-gistcanpredicttherangeofstreamgradientandstreamenergybylookingatamaporanaerialphotograph.

Straight StreamsWhenastreamflowsinachannelwithoutsignificantbends,geologistssayitflowsstraight.Mostcommonlyastraightstreamisonethathassomuchenergyandflowssofastthatitmanagestoerodeitsownchannelregardlessofrocktype.Straightstreamstendtohavesteepsidesandthemostenergy.Theycanpushlargerocksandevenbouldersdownhill.Straightstreamsdemonstratethefasteststreamvelocityandusuallyindicatethatthestreamisdroppingfastfromahigherelevationtoalowerelevation.

Thestreamshowsyouthedirectionofthedownhillslopeevenifyoudonothaveatopographicmap.

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Straight stream map view Straight stream perspective view

Meandering StreamsMeanderingstreamsarethosethatseemtotwistandturninasnakelikepattern.Geologiststendtofindtheminwide,flatareas.Whenastreamgradientislow,thestreamslowsdown.Thenexternalfactors,likefrictionbetweenthewaterandthebankorchannelbottom,alsocanaffectstreamflow.Meander-ing,curvingstreamsoccurwherethewatercurrentisnotstrongenoughtoforceitswaydirectlytobaselevel,butonlyplaysbackandforthacrossa(mostly)flatarea.Meanderingstreamsareoftenclosetoalargerbodyofwater(baselevel)likealake,ocean,oralargerriver.

Intime,thisactionisexaggerated.Theslowerzoneinthestreambeginstodropgrainsofsediment,whichmakesthechannelshallowerasitfillsthechannelbottom.Inashallowchannel,thewaterflowspreadsacrossmoreareaandcreatesmorefriction,whichslowsthewaterevenmore,andsoon.

Anothercauseforastreamtomeandermightbeanobstacleinthechannel;perhapsthestreamflowstoalargeboulderoradifferentkindofrockformationanddoesnothavetheenergy(streamenergy)tomoveitoutofthewayorwashitdownstream.Thelow-energystreamwillflowaroundit.Meanderingstreamstendtohavetheslowestflowandtheloweststreamgradient(energylevel).

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Meandering stream map view Meandering stream perspective view

Dendritic StreamsStreamsthathaveadendriticpattern,resemblingtheveinsinaleaf,tendtobemadeupofbothstraightandmeanderingstreamsegments.Thispatternismostcommoninareasofvaryingelevationasinhillyormountainousterrains.Waterfromonesideofaravinewillruntothebottomandjoinwithwaterfromtheothersideoftheravine.Thecombinedstreamwillflowdownthevalleyuntilitjoinsanotherrunoffstreamfromaneighboringvalley.

Becausewateralwaysrunsdownhill,theintersectionoftwostreamsmakesasouth-pointingarrowpatternonamap.Dendriticstreamsoccupythemiddlegroundbetweenstraightstreamsandmeanderingstreams,wherethestreamisstilldroppingfromhighgroundtolowground,butwherethedropisnotassteep.Thereisstillenoughenergytoshowaprimarydirectionofflow.

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Dendritic stream map view Dendritic stream perspective view

Trellis StreamsTrellisstreampatternsarenotascommonasotherpatterns.Theydisplayastreampatterninfluencedentirelybytheunder-lyingrocks.Inanareawheretherockshavebeenfolded,orthrust-faulted,thesurfacerocksoccurinapatternofparallelridges.Waterwillflowalongthevalleybetweentheseridgesuntilitfindsagapthatallowsittoescapeandflowdowntothenextlevel.Althoughthesestreamsdon’tflowinastraightline,theyflowinverystraightsegmentsandtheirvalleywallsprobablyaresteep-sided.

Trellisstreamsmayhaveveryhighenergyandveryfastwater.Thesofterrocks,whicherodemoreeasilythanothers,erodefrombetweentheharderlayersandleavebehindridgesofhigherground.Theseparallelridgesprinttheirpatternintothestreampatternbecausethewateralwaysrunsdownhillthroughtheerodedvalleysandflowsaroundthehigherridges.

lakesEnvisionalakeasaverywide,slowpartofastream.Astreamusuallyfillsthelakeatoneend,andtheoverflowspillsthroughalowspotsomewhereontheedgeofthelake,allowingthestreamtocontinueitsflowdownhill.Lakesarequiet,stillwater.Thebase leveloccurswherethestreamgradientbecomeszeroandthestreamdropsalltheremaininggrainsfromsuspension.Thereusuallyisverylittlecurrentassociatedwithalakeunlessstormwaterisflowingintotheupperend,sotheveryfinestgrainscansettlefromsuspension.Thecloudinessyouseeinalakeismostlyduetoalgaeandotherlakelife.

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Trellis stream perspective viewTrellis stream map view

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a lake with a river.

a river builDS a Delta aS it enterS the lake.

SeDiment builDup convertS the lake to a Shallow Swamp.

a lake baSin FilleD with SeDiment; only the river remainS.

vanishing lake

Activity 2: Reading Topographic Maps for Stream GradientYounowknowhowtorecognizefourtypesofstreams:straight,meandering,dendritic,andtrellis.Inthefollowingactivity,youwillcalculatethestreamgradientforanexampleofeachtypeofriveranddeterminewhatthattellsyouaboutthestream.

PRoCeDUReSStep 1—Useacontourmapprovidedbyyourcounselor,orusethefourprovidedinthispamphlet.Identifythetypesofstreamsfoundonthemaps.

Step 2—Findastartingandendingplaceonthemapwherethestreamcrossesacontourline.Measureascloselyaspossible

30 GeoloGy

thedistanceonthemapbetweenthepointswitharulerandconvertittofeetormilesusingthescaleonthemap.Ifthedistanceisinmiles,multiplyitby5,280toconvertittofeet.

Step 3—Readtheelevationofthestreamatthebeginningandendingpointsyouselectedinthelaststep.Oftennotallcontourlinesarelabeled,buttheintervalisthechangeinelevationbetweeneachcontourline.Usethisinformationtofindtheelevationofthecontourlinesthatcrossthestream.

Step 4—Calculatethestreamgradient—theratioofelevationchangetodistance.Streamgradientsareexpressedinratioformsotheycanbereducedtothelowestcommondenominator.

Step 5—Repeatsteps1through4withtheremainingthreemaps.

GeoloGy 31

oBSeRvATionS1.Whichtypeofstreamflowsthefastest.Why?

2.Whichtypeofstreamflowstheslowest.Why?

3.Whichtypeofstreamwouldcarrythelargestgrainsofsediment?Why?

4.Whatkindofstreamgradientwouldawaterfallhave?Dowaterfallsflowfastorslow?

ConClUSionSStraightstreamstendtohavethehighestgradientandthemostenergy,andthereforeareabletocarrythemostsediment.Meanderingstreamsnormallyhavethelowestgradientsandtheleastenergy,andareabletocarryonlythesmallestsediments.

Stream landformsIfyouwereaprospectorintheCaliforniagoldrushofthemid-1800s,youwouldhavecarefullyobservedstreamlandforms.

CUT BAnkOnthemeanderingstreamwithitsS-shapedcurves,theforceofwaterpushesontheoutsideofthebend.Therushingwatercontinuestoerode,orcutaway,theoutsideofthebendnamedthecut bank.Justasaracecarintheouterlaneofabendhastotravelfastertokeepupwitharacecaronaninnerlane,thewaterontheoutsideofariverbendtravelsfasterthanwaterontheinsideofabend.Becausethewaterinacutbankishighstreamenergy,flowingquickly,itoftenpicksupdirtandsediment,erodingthecutbank.Typicallynograinswillsettleinthisarea.

PoinT BAR AnD Fill BAnkWhilethewaterontheoutsideofabendtravelsquickly,thewaterontheinsideslowsdownandhaslowstreamenergy.Thiscreatesanareawherethebiggerortheheaviergrainsaredropped.Wheretheinsideofariverbendoftenfillswithsedi-mentiscalledafill bankorpoint bar.

32 GeoloGy

DelTADeltasformwhereastreamflowsintoalakeoroceananddropsitssediment.Deltascanshowdiffer-entpatternsofdepositionbutthereisusuallyanareawherethedeltaendsandtheslopedropsquicklyintodeeperwater.Streamchan-nelscanoccurwithinadelta.Aslongasthestreamhasanyenergytoflowitwillcontinuetomaintainitsformandtransportgrainstothedeltaslopewherethestreamenergydropstozero.

MeDiAl CHAnnel BARAnelongatedmoundofsedimentinthemiddleofachannelorwaterwayisamedial channel bar,sometimescalledasand-bar.Adeltamayhaveanumberofmedialchannelbarsinthewaterwaywherethesedimentsettlesastheflowslowsenter-ingalakeorocean.Grainssettleoutlikeinadelta.

Activity 3: Finding Sediment With a Magnifying GlassLookingatariverbedyouknowtherearesedimentorriverrocksthatarebigenoughtoeasilysee,buttherealsoissomesedimentthatistoosmalltoseewiththenakedeye.Inthefollowingactivity,youwillneedamagnifyingglasstostudystreamwater.

GeoloGy 33

PRoCeDUReSStep 1—Withyourparent’spermissionandaScoutbuddy,visitanearbystream.Usingaclearplasticcup,scoopupsomestreamwater.Usingamagnifyingglass,lookatthewaterforsuspendedsedimentarymaterials.Writedownyourobservations.

Step 2—Findasecondlocationalongthestream,perhapsinafillbank,andscoopupasecondsample.Examineitwithamagnifyingglassandmakenotes.

Step 3—Ifyouhaveaccesstoamicroscope,maybeatyourschool,saveasampleofstreamwaterandlookatthesamewaterthroughthemicroscope.Youmayhavetostirorshakethewaterbeforemakingyourmicroscopeslide.

oBSeRvATionS1.Wereyouabletoseemoresedimentwiththe

magnifyingglass?

2.Wastheremoresedimentinthefirstorsecondsample?

3.Ifyouwereabletouseamicroscope,whatdidyouobserve?

4.Eventhoughsomeofthissedimentistoosmalltoseewithoutmagnification,doyouthinkwhentheriverdropsthissedimentitimpactsthestreambottom?Why?

ConClUSionSSomesedimentistoosmalltoseewithoutmagnification.Riversandstreamsmovematerialsinalargevarietyofsizes,fromlargeboulderstofinegrainstoosmalltobeseenwiththenakedeye.Waterflowingoverourplanetisconstantlychangingtheshapeofitssurface.

Activity 4: Water Direction CluesHaveyoueverhikedacrossadried-upriverbed?Couldyoufindcluestotellwhichwaythewaterhadflowed?Inthefollowingactivity,youwillhuntforriverdirectionclues.

PRoCeDUReSStep 1—Withyourparent’spermissionandaScoutbuddy,visitanearbystream.Lookatthewatertoseewhatdirectionitisflowing.Dropastick,leaf,orothernaturalmaterialonthe

34 GeoloGy

watertoconfirmthisdirection.Evenifthewaterhasdriedup,lookforcluesthatshowthedirectionofthepreviouswaterflow.

Step 2—Lookforasecondstreamfeedingintothisstream.

Step 3—Lookforanobstructioninthestreamlikearockortree.(Onanobstruction,sedimentwillbuildupontheupstreamsideandthedownstreamsidemaybehollowedout.)

Step 4—Lookfordebrisliketwigsandleaveswrappedaroundtreesandrocksalongthebank.

Step 5—Lookforreeds,grass,litterbendingtowarddownstream.

Step 6—Recordallyourobservationswithnotesandsketchesinanotebook.Shareyourobservationswithyourcounselor.

oBSeRvATionS1.Areyouabletoseesedimentbeingcarriedbythe

streamcurrent?

2.IfyoufoundasecondstreamfeedingintothefirststreamdidtheyformaVwheretheyconverged?WhatdirectiondidtheVpoint,upstreamordownstream?

3.Whattypeofobstructiondidyoufind?Whathadcollectedontheupstreamsideoftheobstacle?Wasthedownstreamsideoftheobstaclehollowedout?

4.Didyoufindtwigsandleaveswrappedaroundtreesandrocks?Didtheheightofthisdebrisindicatethestreamonceoverfloweditsbanks?

ConClUSionSEvenifastreamhasdriedup,manycluesindicatethedirec-tionofthewaterflow.OftentwojoiningstreamswillformaVpointingdownstream.Obstructionsliketreesandrockscollectsedimentsasthewaterslowstopassaroundit.Allstreamsleavewater-flowdirectionclues.

GeoloGy 35

36 GeoloGy

What Is a Topographic Map? Geologists use topographic maps, two-dimensional pieces of paper that depict the three-dimensional surface of Earth.

Topography is the shape of the land surface, the “top” of the land. Contour lines, which on a mountain peak look like concentric rings, show elevations. Elevation is the vertical height above sea level. The contour lines connect points of the same elevation. Closely spaced contour lines indicate steep slopes. Contour lines far apart represent gentle slopes. In the topographic map below, the contour interval is 100 feet. This interval is the difference in elevation between each contour line.

This “topo” map shows contour lines and a study line (transect) from point A to point B.

you can draw a profile across the valley by marking elevation points along the study line (transect A to B). Use graph paper if you can.

.energy From our earth

GeoloGy 39

EnergyFromOurEarthEnergyisthevitalforcepoweringbusiness,manufacturing,andthetransportationofgoodsandservicestoservetheUnitedStatesandworldeconomies.Energysupplyanddemandplaysanincreasinglyvitalroleinournationalsecurityandtheeconomicoutputofournation.ItisnotsurprisingthattheUnitedStatesbudgetsmorethan$500billionannuallyonenergy.

natural ResourcesNaturalresourcesareveryimportantinourdailylives.Allnaturalresourcesmustbefound,extracted,andprocessedbeforetheycanbeused.Manyareessentialtoourwell-being,andothersareimportantforourcomfort.Rockisquarriedandcrushedforconstruction.Oreisminedandrefinedformetals.Petroleum(oilandnaturalgas)isusedforplastics,medicine,andtransportation.Coalisusedforheatandelec-tricity.Gemstonesareusedforjewelry.Thelistofnaturalresourcesisendlessanddiverse.

Findingnaturalresourcesmaybeassimpleasknowingthesurfacerocksinthearea,orascomplexaslookingthreemilesormoreunderground.Extractionmaybeassimpleasdredgingsandfromariverbedorasdifficultasblastingashaftthou-sandsoffeetundergroundandbringingtheoretothesurface.Transportingmaybeassimpleasloadingthematerialonatruckorascomplexaslayinga250-milepipeline.Thecostofextractionandtransportationmustbeconsideredindetermin-inghowvaluableanEarthresourceistosociety.

MostoftheenergyresourcesweusetodayaretakenfromEarth.Theenergytoheatyourhomeandschool,theenergytopushyourfamilycarorneighborhoodbusdownthestreet,theenergyrequiredtolifta747airplaneofftherunway—allcomefromEarthandfromEarth’spast.Becauseageolo-gist’sresponsibiltyistofindnewsourcesofEarthresources,theresponsibilityoffindingnewenergysourcesfallsintothegeologist’shandsaswell.

GeoloGy 41

When geologists

refer to gas or

natural gas, they

are talking about

the natural gas

used in a water

heater or in

heating a home.

energy From our earth.

Where Do We Get electricity?IntheUnitedStates,ourenergycomesfromanumberofsources.Electricityisusedforpowerandheat,andtooperateappliancesandelectronics.Electricityiscleanandeasytouse.Butwheredoeselectricitycomefrom?

AccordingtotheU.S.DepartmentofEnergy,electricalgenerationcomesfromcoal(51percent),nuclear(21per-cent),naturalgas(17percent),hydroelectric(6percent),fueloil(3percent),andallothersourcescombined(2percent).Whileitisimportantthattoday’ssocietycontinuetodevelopwind,solar,andotherenergyresources,it’sclearthatwestilldependoncoalformorethanhalfourelectricity.

CoalCoaloccursinbedsbetweenlayersofothersedimentary

rocks,suchasshaleandsandstone.Coalisformedwhenmaterialfromancientplantsaccumulatesinswampsorbogsandbecomesburiedunderwaterandsediments.Thisprocessstopsthedecayofwoodedmaterialbysealingofftheoxygensupplyneededfordecay.

Coalformsindifferentstages,dependingonhowlongithasbeenburiedandhowmuchpressureandheathavebeenappliedduringcompaction.Initsfirststage,coaliscalledpeat.Ifdried,peatcanbeburnedasafuel.

Withmoretime,heat,anddeeperburial,morewaterisdrivenoutofthepeat,creatinglignite,orbrowncoal.Ascontinuedburialdrivesoffmorewaterandthepercentageofcarbonisincreased,lignitebecomesbituminous coal,themostcommonandwidelyusedformofcoalintheUnitedStates.BituminouscoalisfoundthroughoutNorthAmerica,butthedepositsfoundinmanystatesarenotlargeenoughtobeeconomicallydeveloped.Ifbituminouscoalisfoldedduringburial,theaddedpressureandheatoffoldingchangesittotheveryhighestgradeofcoal,anthracite.

42 GeoloGy

otherFuel oil

hyDroelectric

natural GaS

nuclear

oil and natural Gas Livingthings,likeplantsandanimals,aremadeofthesamebasicbuildingblocksasoil,gas,andcoal—thecarbonandhydrogenatoms.Scientistsbelievethatoilandgasformedfromdeadplantsandmicroscopicorverysmallanimals,preservedinmudonthebottomofseasandlakes.Tobepreserved,theseplantsandanimalshadtobequicklycoveredwithmudsooxygencouldnotdecaythem.Duringburial,bacteria,heat,andpressureforcedchemicalchangesintheplantandanimalmaterialuntilthecarbon-basedmoleculesbecameoilandnaturalgas.

Whiletheplantandanimalmattersettledontheoceanfloor,grainsofsandorclaywereburiedandpackedintorock.Likemarblespackedinajar,therewerespaces,orpores,filledwithorganicmaterial,water,andmostlyclay.Astheorganicmaterialconvertedintooilornaturalgas,itmigratedupthroughthesepores.

GeoloGy 43

Rock where the

oil and gas form

is a source rock.

Toseeforyourself,fillabottlewithcookingoilandwater.Capitandshake.Watchtheoilseparatefromthewaterandrisetothetop.Sinceoilandgasarebothlighterthanwater,theydothesamethingdeepunderground.Theoilandgasriseuntiltheycometoatrap—anonporousrockbarrierthattrapsthemigratingoilandgas.Sometimesoilandgaswilltravellongdistancesandcollectinalargetrap,creatingagiganticoilandgasreservoir.Theporousrockbelowthetraprock,saturatedwithoilandorgas,isthereservoir rock.

Fewrocklayersareperfectlyhori-zontal,anditiscommonforporousfoldedortiltedbedstobecomeoilorgasreservoirs.Thehighestpointintheformationbecomesthereservoir,sothegeologisthuntingforoilornaturalgaslearnstolookforthesehighspots.Thescienceofpetroleumexplorationisthesearchfortheseporousrockssealedbyimpermeablerocks.Thesefoldedstructuresarecalledanticlines, synclines,anddomes.Eachtypehasadifferentcharacteristicandcantrapoilorgasinadifferentmanner.

Notalltrapsareanticlinesordomes.Oilcanbetrappedintiltedlayersagainstanimpermeablezone,suchasasaltdomeorafault.

Sometimes if an impermeable barrier does not stop the migration of oil and gas, it will leak out on Earth’s surface in a natural seep. There are natural seeps in the United States, notably in the Gulf Coast area and in California.

44 GeoloGy

Syncline: fold arching downward

Dome: inverted bowl shape

Anticline: fold arching upward

oil ShaleOilshaleisaspecialkindofshalerockthatisformedbyplantandanimalmatterdepositedtogetherwithmudinanoceanorlakebottom.Theplantandanimalmattercompactedwiththemudconvertstoasubstancecalledkerogen.Oil,gas,coal,andkerogenareallhydrocarbons,madeofhydrogenandcar-bonatoms.Oilshaleisminedlikeanyotherrock.Itisthenheatedtoreleasethekerogen.Colorado,Utah,Wyoming,andCanadaallhaveenormousdepositsofoilshale.Atthistimeitisexpensivetominetheoilshaleandremovethekerogen.Oilshaleisnoteconomicaltomine.

nuclear energyAnuclearpowerplantusesuraniumfornuclearfission,whichproducesheattoboilwater,whichthenturnssteamturbinestogenerateelectricity.Uranium,aheavymetalelement,comesmainlyfromamineral,uraninite,butalsocancomefromcarnotiteandautinite.TheUnitedStateshasradioactivemineraldepositsinNewMexico,Utah,Colorado,Wyoming,Arizona,andWashington.

GeoloGy 45

containment builDinG

reactor

Steamelectrical

power tranSmiSSion

GeneratorturbineconDenSor

coolinG tower

nuclear core

boilinG water

control roDS

Creating nuclear energy

Hydropower Damsproducepollution-freerenewableenergy.Justasthewheelinawatermillturnsundertheweightoffallingwater,adam’sturbinewheelalsoturnsundertheweightoffallingwater.Thedifferenceisadam’sturbineisattachedtoanelectricgenerator.

Thebenefitsofdamsincludesupplyingwaterforagri-cultureandcommunities,andreducingtheriskoffloodsanddroughts.Oneoftheirfewdrawbacksistheblockedsedimentflow,whichdeprivesthedownstreamfloodplainsoffertilesediment.Anotherdrawbackisthatdamsserveasalargesourceofevaporation,whichcanchangethelocalclimate.

Mostsuitablesitesforlargedamsindevelopedcountrieshavebeenexploited.Forthisreason,hydroelectricpowerproductionisnotexpectedtoincreasesignificantlyintheUnitedStates.

Wind Windcanturnlargewindmillsthatgenerateelectricity.Infact,windmill“farms”canbeseenthroughoutthewesternUnitedStates.Foryears,ranchersandfarmershaveusedwind-drivenpumps,nottogenerateelec-tricity,buttosaveelectricity.Thesepumpsbringwatertothesurfaceforlivestocktodrink,savingtheranchertheexpenseoftak-ingelectricitytodistantpasturesorthetimebringingthelivestocktothecorraltodrink.Althoughwindenergycanbeinexpensivetogenerateandthelandittakesupcanbemulti-use,ithasitsdrawbacks.Windenergyrequiresalargeareaandsteadywind.

Tidal Power Tidalpower,wherewaterfromarisingtideistrappedbehindgatesofalargeimpound-ment,isusedonalimitedbasis.Asthetidedrops,thewaterisslowlyreleasedthroughturbinegates,generatingelectricity.Thisenergysourceisrelativelyinexpensivebutrequiresalargecoastalareaandmaydam-agethelocalshorelineecosystem.

46 GeoloGy

Solar energy Solarenergycouldbecomeanimpor-tantenergysourceinthefuture.Solarenergycurrentlyhelpssaveelectricitybyheatingwaterforhomesandbusi-nesses.Also,allNASAspacecraftusesolarenergytopowerinstrumentsandcommunications.

Geothermal energyInareaswheremagmaisrelativelynearthesurface,watermaybepipeddownclosetothemagma.Theextremelyhotmagmaboilsthewater,producingsteamthatrisesthroughthepipeoutofthegroundtoturnaturbine,whichgenerateselectricity.

exploring for oil and GasGeologistshaveseveralhigh-techtoolsintheirtoolboxthathelpthemfindoilorgas.Theyusethesetoolstomakeamapofwhattheyexpecttofindunderthesurface.Ageologist’smapisaneducatedguessofsomethingageologistcannotsee.

Studying Rock layersSedimentstendtocollectinregionalbasins,orbowl-shapedareas,wherewateraccumulatesanddepositssediments.Geologistsstudyandrecordabasin’sstratigraphy—itsrocklay-ersfromthesurfacedowntothebasement.Theyknowthatifacertainrockformationisareservoirforoilandgasinonepartofthebasin,italsomaybeareservoirelsewhereinthesamebasin.Ifacertainrockisfound8,000feetbeneaththesurfaceinonepartofthebasin,itmightalsobefoundatasimilardepthinotherpartsofthebasin.Usingtheverticalsequenceinonepartofthebasintohelplocatearockformationinanotherpartofthebasinisknownasstratigraphic correlation.

Someofthetoolsageologistusestotraceaformationinthesubsurfaceincludereflectionseismic,electricalwelllogs,coresamples,andcuttings.

GeoloGy 47

The basement

rock is igneous

rock—rock

formed from

molten material

that makes up

Earth’s crust

and underlies

all basins.

Although solar energy is abundant, it requires a large area and sunny days. Scientists also are discovering how to store solar energy and make today’s solar panels more efficient.

Ageologistmustbeabletoseewhatliesburiedbeneaththesurfaceofthegroundorunderwaterinordertolocatereservesofoilandnaturalgas.Reflectionseismicistheprocessofsend-ingacoustic waves (soundwaves)throughEarthusingawaveenergysourcefromeithermechanicaldevicesorexplosives.Thengeophones(earthmicrophones)detectthereflectionsastheybouncebacktothesurface.Computersmeasurethetimeittakesforthewavetotravelround-trip,thenusethatinforma-tiontocreateusefulgraphicdisplaysofthesubsurfacelayersorstructureswhereoilornaturalgasmayaccumulate.

TheseacousticwavestravelthroughEarth’slayersandarereflectedbacktothesurfacefromrockformationboundaries.Formationboundariesusuallyaredefinedwheretherocktypechanges(forexample,sandstonetolimestone).

48 GeoloGy

Just as bats use sound echos to locate flying insects, scientists use reflections of seismic waves to locate underground rock structures that might contain minerals or oil and gas.

hiGh-pitcheD SounD From bat

echo reFlecteD From moth

eleCTRiC Well loGS Electric well logsareelectricalmeasurementstakeninawellafterithasbeendrilled,tocreatearecordofthestratigraphyandrockpropertiesencounteredinthewell.Electricalcurrentispassedthroughtherockformationusingalong,cylindri-calsonde,aspecialtoolconnectedbywiretoacomputeronthesurface.Thesondemeasureshoweasilyelectricitypassesthroughtherockformation.Bycomparingthiselectricalcon-ductivitytorockpropertiesinotherpartsofthesamebasin,geologistscanpredicttherockformationsinotherpartsofthebasin.Engineersusethewelllogtodevelopaplanofhowtobestdrillandrecovertheoilandgas.

GeoloGy 49

tranSmitter

electrical SiGnal paSSinG throuGh rock Formation

receiverS

in an electric well log, the sonde first takes the electric readings in the well. Then the readings are plotted on a graph against the depth to produce a well log. in the final step, a geologist can use the well log to draw a geological cross section, spacing the well logs in proportion to the actual wells.

Core SamplesTypicallyseismicand/orwelllogsprovidetheinformationneededtobegindrillinganewwell.Occasionallygeologistsandengineerstestaspecialcylinder-shapedrocksamplecalledacore sample.Laboratorytestingcantelltheengineerrockporosity,theamountofspacebetweentherockgrains.Aspecialhollowdrillbit,shapedlikeastraw,cutscoresamplesandbringsthemtothesurface.Coresamplesareoften1to21⁄2inchesindiameteryethundredstoeventhousandsoffeetlong.

Asthedrillbitdigsdeeperintherock,grounduprockpiecescalledcuttingscometothesurface.Ageologistcomparescuttingstowhatwasexpected.Thecuttingsrevealifthepredictedverticalsequence,stratigraphy,needstobemodifiedandgivethedrillercluestoknowwhenthebithasreachedthetargetrockformation.Cuttingsaresavedforothergeologiststoexamineforcluesabouttherockformationsinotherpartsofthesamebasin.

50 GeoloGy

Core samples

Make a Core SampleTo better understand core samples, try this for fun. Cut the top off a 2-liter plastic drink bottle. Mix equal parts of sand and dry plaster of paris. Fill the bottom 3 inches of the bottle with this mix. Now mix equal parts of dirt and plaster of paris. Make a second layer in the bottle with the dirt mixture. Sticks, seashells, and leaves may be added between layers in your core sample. Mix equal parts of gravel or rocks with plaster of paris and add for a third layer. Now add layers, in the thickness and order as you wish, to fill the bottle. Fill the bottle with water. The next day remove your core sample.

Making the exploration MapGeologistsmakemapsofthingstheycannotseefrominforma-tiongatheredwithseismicsurveys,welllogs,coresamples,andcuttings.

Afirstpassinanewbasinmightincludeaseismicsurveytoproduceapictureofthesubsurface structures,whichincludetopsofformationsandotherundergroundfeatures.Thebestseismicsurveysallowgeologistsandgeophysiciststocomparewhattheyalreadyknowaboutthebasinstratigraphywiththestructuresintheseismicprint.

Ifthebasinareahasbeenexploredbefore,geologistswilluseelectricwelllogplotsfromnearbywellstoestimateatwhatdepthtoexpectoilandgas.Theycanbuildasubsurface structure mapusingthedepth-to-formationnumbersfromthewelllogplotsandmayusethesametechniquetorevealthebottomoftheformationanddetermineitsthickness.Thissubsurface isopach mapshowsthepotentialthicknessofthetargetreservoir.

Astructural maprepresentsseismicdatameasuredfromthesurfacetoaparticularsubsurfacerocklayerofinterest.Thesemeasurementsaregivenavalueintimeordepthandareplacedonamapatregularintervalsfromeachotheraccordingtothesurfacelocationoftheseismicdata.Thefinishedmaplooksmuchlikeasurfacetopographicmap,butitisthesubsurface.

Activity 5: Drawing a Subsurface Structure Map Contourmappingislikedrawingaconnect-the-dotspuzzle.Makingasubsurfacestructuremapislikemakingatopographicmap,exceptthatthemapisoftheburiedtop(orbottom)ofaparticu-lartargetrockformation.Inthisactivityyouwilllearnhowtodrawasubsurfacestructuremap.

Theelevationusedonmostsubsurfacestruc-turemapsareshowninnegativenumberstoshowhowfarthesevaluesarebelowsealevel.Sealevelbecomesadatum,orastandardreferencepositionknowninallwells.Theelevationatsealeveliszero.

GeoloGy 51

Ifyourcounselorhasaccesstowelldata,usethattomakeasubsurfacemap.Perhapsyourcounseloralsowillhavecopiesoftheelectricwelllogsfromwhichthisinformationwastaken.Otherwiseusethedatainthefollowingchart.

PRoCeDUReSStep 1—Thedepth-to-structurevaluesarenegativebecausetheyarebelowsealevel.Tomakemappingsimpler,add6,200feettoeachdepthintheblankcolumn.

Step 2—Traceorcopythewelllocationmapandlabeleachwellwiththedepthbelow6,200feetyoucalculatedinstep1.

Step 3—Lookattheelevations.Decideifyouwouldliketodrawcontourlineson50-footintervals.Findthelowestpoint.

Step 4—Youmaywanttousedashedorlightpencillinesuntilafteryouhavecheckedthepointsinstep7.Drawalinebetweenthefourlowestpointsforthe–600-footcontourline.

Step 5—Nextdrawthecontourlinefor–550feet.Doesthislineintersectpoints?

52 GeoloGy

Well number Depth to Structure (Subsea) Feet +6,200 Feet

1 -6,790 580

2 -6,810 610

3 -6,840 640

4 -6,435 235

5 -6,241 41

6 -6,438 238

7 -6,294 94

8 -6,489 289

9 -6,750 550

10 -6,555 355

11 -6,750 550

12 -6,780 580

13 -6,805 605

14 -6,350 150

15 -6,395 195

16 -6,428 228

17 -6,463 263

18 -6,658 458

19 -6,679 479

20 -6,742 542

Step 6—Continuesketchingincontourlinesbetweenpointsuntilyoureachthehighestelevation.Remember,contourlinescannotcrossoneanother.

Step 7—Double-checkyourcontourlines.Makesure,forexample,anelevationof–289doesn’tfallbetweenthe–300andthe–350contourlines.

Step 8—Lookforastructuralhigh,theplaceofthehigh-estrelativeelevation.Itlookslikeahilltopofatopographicmapbutactuallyisthestructurallyhighestpointonthemap.Sinceoilandgasarelighterthanwater,theymigrateupwardthroughtherockandcollectinastructuralhigh.Labelyourmapwhereyouwouldexpectanoilreservoirtoexist.

oBSeRvATionS

1.Isthelowestpointwell3or5?Why?

2.Aresomecontourlinesspacedoutmorethanothers?Whereisthesteepestsectionoftheformation?

GeoloGy 53

ConClUSionSThree-dimensionalsurfacescanbeclearlyseenonacontourmap.Drawingacontourmapshowshillsandvalleysthatwouldbedifficulttofindbyreadingthewelldata.Asubsurfacemapisanimportantgeologicaltool.

offshore Drilling.Oilcompaniescandrillwellsondrylandorindeepwater.Someoffshore platformsstandinwaterhundredsoffeetdeep,andothersdrillinwatersodeeptheplatformdoesnoteventouchtheoceanfloor.Theseplatformsfloatlikesmallislandssurroundedbywater.

Becauseitissodifficultandexpensivetodrilloffshore,oilcompaniestrytodrillmorethanonewelloncetheysetupadrillingplatform.Theycandrillwellsindifferentdirectionsfromthesamelocation,usingthesamehole.

Activity 6: extraction Tabletop DisplayThegeologisthaslocatedalargeoilandgasreservoir.Nowwhathappens?Forthisactivity,makeatabletopdisplayandshareeitheroilandgasextractionorcoalextractioninforma-tionwithasmallgrouporyourcounselor.

PRoCeDUReSStep 1—Chooseoilandgasorcoalasyourfocus.(Oilandgasoftenarefoundtogetherinonereservoir.)Makeathree-paneldisplayboard.Addonelargelabelinthecenterthatreadseither“OilandGas”or“Coal.”Thethreelabelsforthethreepanelscouldbelabeled“Exploration,”“Extraction,”and“Processing.”

Step 2—Withparentalpermissionandalibrarian’shelp,searchthepubliclibrarydatabasesforarticlesonoilandgasorcoal.Withparentalpermission,exploretheInternetusingasearchenginefortermslike“oilexploration”or“coalmining,”for

54 GeoloGy

isopach Map. Whenever geologists make a structure map of the bottom of the formation, they can calcu-late the thickness by subtracting the depth of the top from the depth of the bottom. This map showing formation thickness is called an isopach map and can help the geologist or engineer determine whether there is enough rock formation present to make a sufficient reservoir for oil or gas.

example.Byputtingthewordsinquotes,thesearchenginewillpulluponlyWebsitesthathavebothwordstogetherinthecontent.

Step 3—Decorateyourdisplayboardwithinterestingfactsyoufoundonextraction.

Step 4—Giveafive-minutepresentationonyourfindingstoasmallgrouporyourcounselor.

oBSeRvATionS1.Aregeologistsmoreinvolvedinexploringforoil,gas,and

coalorprocessingit?

2.Whatissomethingyoulearnedintheresearchyoudidnotknowbefore?

3.Arethereoil,gas,orcoalreservesinyourstate?Whatstatesdohaveoil,gas,orcoalreserves?

4.Doesyourhomeusenaturalgas?Ifyes,inwhatways?

ConClUSionSTheexploration,extraction,andprocessingofoil,gas,andcoalisafascinatingbusiness.Nowyouunderstandthatbythetimeyoupumpgasolineintoyourcar,manypeople,includinggeologists,haveworkedtofind,extract,andprocesstheoilforthegasoline.

GeoloGy 55

Activity 7: visit an operating Drilling RigWouldyouenjoyworkingonanoil-drillingrigasageologist?Completethisactivitytofindout.

PRoCeDUReSStep 1—Askyourmeritbadgecounselorforassistancewithfindingageologistwhoworksonadrillingrig.Youmightlocateageologistinyourareabycontactingageologicalgrouplistedattheendofthispamphlet.Withpermissionfromyourparentandcounselor,telephoneore-mailthiscontact,explainingyouareworkingontheGeologymeritbadgeandthatoneoftherequirementsistovisitwithageologistatadrillingrig.

Step 2—Visitthegeologistatworkandasktoseewhatgeolo-gistsdoonsite.Asktoseecuttingsamples.

oBSeRvATionS1.Whatisdrillingmud,

andwhatpurposedoesitserve?Whataredrillbitsanddrillpipe?

2.Howmanybarrelsofoildoesthegeologistthinkthereservoirholds?Howmanygallonsofoilisthat?(Thereare42gallonsinabarrelofoil.)Howmuchoftheoilisexpectedtoberemovedorrecoverable?

3.Askthegeologistwhatisthemostsatisfyingpartofworkingonadrillingrig.Wasithardgettingageologydegree?Whydidthegeologistpickthiscareer?

ConClUSionSVisitingadrillingriggivesyouaglimpseofwhatageologist’sdailylifecanbelike.

56 GeoloGy

The magnificent blue Hope diamond, at more than 45 carats, sparkles for visitors at the national Museum of natural History, Smithsonian institution, in Washington, D.C.

.Minerals: earth’s Treasures

Minerals:Earth’sTreasuresRocksareamixtureofoneormoremineralsfoundonEarth,otherplanets,moons,andmeteorites.Somerocks,likemarble,containonlyonemineral—calcite.Tobeamineral,asub-stancemustbeanaturallyoccurringcrystallinesubstance.Forinstance,theHopediamondformedasacrystalinnature,notinalaboratory.Itmustbesolidandhomogeneous,orthesamethroughout,liketheHopediamond.Itmustalsohaveadistinctivesetofphysicalandchemicalproperties.Adiamondisthehardestmineral,andthehardestsubstance,knowntohumankind.Thisisdefinitelyauniquephysicalproperty.

GeoloGy 59

Gems—minerals like amethyst that are highly valued for their beauty—are often used in jewelry.

Minerals: earth’s Treasures.

MineralsCommonmineralsincludecalcite,quartz,feldspar,mica,pyrite,andgypsum.Becausethesechemicalelementscombinetoformminerals,geologistsknowthatthemostcommonmineralsarethosecomposedofthemostcommonelements.ThemostabundantelementsinEarth’scrustareoxygenandsilicon(about74percentofEarth’scrust),soitshouldbenosurprisethatthemostabundantmineralsaresilicates—compoundsofoxygenandsilicon.

Thesecommonmineralsmaybeunfamiliartoyoubecausemanypeoplearefascinatedwiththelesscommonminerals,suchasmetallic,silverygray,andcubicgalena.Butidentifyingmineralsisanimportantstepinrecognizingthepotentialeco-nomicvalueofasubstance,oreveninidentifyingrocksyoufindonvacationorinyourownbackyard.Geologistsdidnothavesophisticatedelectronicequipmentwhenthefirstminer-alogistswereidentifyingminerals,sotheydevelopedaseriesofcomparativescalestodetermineamineral’sphysicalproper-tiesandthentoidentifytheminerals.

A geologist

who studies

minerals is called

a mineralogist.

Relative abundance of elements in earth’s crust

Silicon 27.7 percent

Aluminum 8.1 percent

iron 5.0 percent

cAlcium 3.6 percentSodium 2.8 percent

potASSium 2.6 percentmAgneSium 2.1 percent

All otherS 1.5 percent

oxygen 46.6 percent

60 GeoloGy

Acomparativescalecomparesasinglepropertyamongspecimens.Forexample,onekindofmineralmaybedarkerredthanotherredmineralsinthesamerock.Soyoususpectitisadifferentmineralfromtheothers.Whenyoucompareittoarockcolorscale,youcanseeitscolortoneisbetweentwovaluesonthescale.Geologistsrecordthisscalevalueintheirnotes,becauselateritmightbeimportantinformation.Mostmineralscanbeidentifiedusingacombinationoftwoorthreeofthefollowingeightphysicalproperties:hardness,specificgravity,color,cleavage,fracture,luster,crystalform,andstreak.

HardnessYouwouldn’trubyoursunglassesacrossconcretebecauseyouknowtheconcreteisharderandwillscratchthem.Inthesameway,amineralissaidtobeharderthananothermaterialifitcanscratch,orcutinto,it.

Thehardnesstestisascratchingtest.Scratchonemineralagainstanothertodetermineifitwillscratchtheother.Hardermineralswillscratchsofterones.Mineralogistshavedeter-minedanumericalscale,basedontherelativehardnessofcommonminerals.ThisiscalledtheMohs’scale.

GeoloGy 61

Ifyouwanttoknowwhatquartzcanscratch,readtheMohs’scale.Quartzhasahardnessof7.Thismeansquartzcanscratchanythingwithahardnessoflessthan7.Quartzwillscratchaknifebladewithahardnessof5.5andcertainlyyourfingernailwithahardnessof2.5,butwillnotscratchadiamondwithahardnessof10.Infact,nothingscratchesadiamond—itisthehardestmaterialknown.

Thishardnessscalewouldbeusefulifyoufoundamineralandwonderedifitwasfluoriteorcalcite,whichsometimeslookalike.Tryingthehardnesstestonacopperpennywithahard-nessof3.5willtellyou.Fluoritecanscratchapenny,calcitecannot.Why?

62 GeoloGy

It is sometimes confusing which material is scratching which, like writing on a driveway with chalk. The chalk is worn down, leaving dust without scratching the concrete, so the concrete would be considered the harder of the two materials.

Mohs’ Comparative Scale of Relative Mineral Hardness

MineralScale of Hardness Common Use of Mineral

Common Materials With Similar Hardness

Talc 1 Talcum powder

Gypsum 2 Plaster of paris Fingernail 2.5

Calcite 3 Cement Copper penny (pre-1973) 3.5

Fluorite 4 Fluoride in toothpaste

Apatite 5 Fertilizer Steel nail 5

Orthoclase 6 Artificial teeth Knife blade 5.5

Quartz 7 Quartz watch Quartz sand in porcelain

Glass 6 to 7 Streak plate 6.5 to 7 Hardened steel file 7+

Topaz 8

Corundum(ruby, sapphire)

9 Ruby or sapphire for jewelry or lasers

Diamond 10 Jewelry and cutting tools

Specific Gravity Specific gravityistheweightofasubstancecomparedwiththeweightofanequalamountofwater.Aheavymateriallikeleadwillhaveahighspecificgravity.Alightermateriallikealuminumhasalowerspecificgravity.Ageologistusesthisrelativeweighttoquicklysortthroughacollectionofminerals,placingheavieronesinonecategoryandlighteronesinanother.

ColorMineralsallhaveacolor,andcolorispossiblythemostcommon—yetleastreliable—mineraltest.Mineralscanhaveimpurities,orelementsnotnormallyinitscrystalstructure,thatchangeitscolorappearance.Thepurpleamethystisactuallyamilkyorclearquartzcrystalwithtracesoflithium.Becausethecolorcanbemisleading,geologistsusecolorasafirst-passcomparisonbeforeperformingothertests.

GeoloGy 63

The lead sinker is the same size as the aluminum foil ball but weighs more because it has a higher specific gravity.

Fracture and Cleavage Amineralissaidtofractureif,whenstruckagainstahardobject,themineralbreakswithuneven,orirregular,surfaces.Somedifferenttypesoffracturesarehackly,uneven,andconchoidal.

Amineralissaidtocleaveifitbreaksalongsmoothsurfacesandinregulardirections.Mineralsthatchemicallybondtoformlayerswillcleavewhenbrokenapart,leavingsmoothersurfaces.Cleavagecanbeadefiniteindicatorformineralidentification.Fractureistheapparentlackofcleav-age,andthatinformationalsoisadefiniteindicator.

luster Lusterreferstotheappearanceofthemineralinnormallight.Mineralsthatlooklikeglassaresaidtohaveaglassyluster.Mineralswithadull,dirtyappearancearesaidtohaveanearthyluster.Mineralsalsocanappearwaxy,oily,silky,ormetallic.

64 GeoloGy

Calcite forms rhombic forms; salt forms cubes; mica forms sheets; and quartz does not have cleavage, but forms a conchoidal fracture when broken.

Calcite

Mica Quartz

Crystal Form Whenamineralsolutionisallowedtocoolslowly,crystalscangrow.Amineraltakesacrystalformifitisallowedtogrowwithoutconstraint,butthelackofacrystalshapedoesnotruleoutanyparticularmineral.Geologistscanidentifycertainmineralsbytheircharacteristiccrystalshape.

Forexample,quartzmayforminavolcanicsteamvent,wherethequartzisdepositedonemoleculeatatimeonthesidesoftheventopening,allowingtimeforthequartztoformintocrystals.Graniteformingundergroundcontainsquartz,butthisquartziscrowdedbyothermineralsanddoesnotformlargercrystals.

GeoloGy 65

Galena HalitePyrite

Galena Quartz Pyrite

QuartzQuartz orthoclase

StreakStreakisthepowderyresidueleftwhenamineralisdraggedacrossapieceofroughporcelain.Suchapieceofporcelain,whichhasahardnessofabout7,iscalledastreak plateandiscarriedinthefieldorusedinthelab.Sometimesamineral’sstreakissurprisingbecauseitscolorisdifferentfromtherockcolor.Forexample,theironminerallimoniteisyellow,butitsstreakisdarkbrown,typicalofanyironmineral.

RocksArockisanaturallyoccurring,solidsubstancecomposedofamineraloramixtureofmineralsthatformanessentialpartofEarth’scrust.Therocksdescribedbelowarefoundworld-wide,oneverycontinentandineveryoceanbasin.Therearethreebasicclassesofrocks,classifiedbytheprocessthatformsthem:igneous,sedimentary,andmetamorphic.

Sedimentaryrockscover75percentofthecontinentallandmass,butthisisathincovering,liketheskinofanapple,andisonly5percentofEarth’smaterials.Igneousandmetamorphicrockscomprisetheremaining95percent.Igneousrockscoveredbyathinlayerofsedimentsformtheoceanfloors.

66 GeoloGy

Magma is molten rock. Descending into Earth’s interior, the temperature rises to where rock melts. Magma may be completely liquid or a mixture of liquid rock, gases, and crystals. When molten rock flows out onto Earth’s surface, as with a volcano, it is called lava.

igneous RocksWhenmagmacoolsandsolidifies,itformsigneousrock.Therearetwobasictypesofigneousrocks—extrusiveandintrusive.

SometimesmagmareachesEarth’ssurfaceasalavaflow,whereitquicklycoolstoformextrusiveigneousrock.Manyofthemineralsthatmakeupextrusiverockscoolveryquicklyandproducecrystalssmallerthansugargrains.Extrusiveigneousrockswithverysmallcrystalgrainsaresaidtobefine-grained—basaltisoneexample.BasaltflowsarefoundinmanypartsofthewesternUnitedStates,forexample,theColumbiaRiverareainWashingtonandtheareaaroundPhilmontScoutRanchinNewMexico.ThenewrocksformedwhenMountSt.Helensvolcanoeruptedin1980aremostlybasalt.

GeoloGy 67

Extrusive igneous

rocks form on

Earth’s surface;

intrusive igneous

rocks form

underground.

upper mantle

lower mantle

D-Double-prime layer

outer core(molten)

inner core(SoliD)

250 mileS

406 mileS

1,688 mileS

1,806 mileS

3,219 mileS

3,981 mileS

earth’s layers

active volcano

volcanic iSlanD

SemiliquiD mantle

riSinG maGma

IgneousrocksthatcooldeeperinsideEartharecalledintrusiverocks.Theyhaveacoarse-grainedtextureandmineralcrystals,orgrains,aroundthesizeoffingernails.Examplesofcoarse-grainedintrusiveigneousrockincludedioriteandgranite.

Occasionally,igneousrockscalledporphyryform.Porphyriesexhibittwostagesofcoolingwithlargecrystals(calledphenocrysts)embeddedinafine-grainedgroundmass,whichmakesthemlooksomethinglikeachocolatechipcookie.

Threecharacteristicsofigneousrocks—texture, color,andmineral content—areusefulinunderstandingtheirnatureandorigin.

• Textureindicatesthecoolingtimeandpossiblelocation(depth)oftheigneousrockwhenitformed.

• Colorisusefulinunderstandingthecompositionofthemagmafromwhichtheigneousrockformed.

• Themineralcontentorchemicalcompositionoftherockisusedtoclassifythekindofigneousrockthatisfoundinthefield.

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When igneous

rocks cool so

quickly that

mineral grains or

crystals do not

have time to form,

the rocks form

a volcanic glass

called obsidian.

Obsidian was

highly prized by

Indians for making

arrowheads.

Devils Tower in Wyoming shoots upward in basalt pillars, an igneous rock.

Rock texture,orgrainsize,providesinformationaboutthe depthatwhichthemineralsinthemagmabegantocool,formingigneousrocks.Asanexample,ifyoufindafine-grainedigneousrock,youinterprettherocktobeanextrusiverockthatcooledatornearthesurface,asinavolcaniceruptionorlavaflow.Coarse-grainedigneousrocksareintrusiverocksthatcooledoververylongperiodsoftime.Thesedeeprocks

gettothesurfacewhentectonic(mountain-building)forcesuplifttheareaandthematerialcover-ingtheintrusiverockiserodedawaybywindandwater.

Anotherimportantcharac-teristicofigneousrocksiscolor,whichindicatesthekindsofrockminerals.Lightercoloredigneousrockssuchasgraniteareusuallyformedfromsialicorsilicicmagmas,richinquartzandfeldspar.Darkercoloredigneousrockssuchasblackorgreencoloredgabbrosorbasaltsareformedfrommaficmagmas,richinironandmagnesium.

Sedimentary RocksSedimentaryrocksareformedfromsediments,thebrokenandweatheredproductsofexistingrocksandminerals.Gravel,sand,andmudeachcanbesedimentsthatformlayers.Asthesesedimentarylayersareburiedinthesubsurface,theybecomesolidsedimentaryrocks.Thepackedsedimentleavesroominporesbetweentheindividualgrainsforwaterand,sometimes,oilandgas.Ingeneral,sedimentaryrocksareoftwoclasses,clasticandnonclastic.

Clastic sedimentary rocksaremorecommonthannonclasticrocks.Theyareformedwhenrockgrainsdropfromacurrentofwaterorwindandturnintolayersthatbecomearockfor-mation.Clasticsedimentaryrocksthatformwhengrainsarecarriedbythewindandgatherinlandareaslikesanddunesarecalledeolianrocks.Thesesedimentsundergoaprocessofrock-formingcompactioncalledlithification.

70 GeoloGy

Clasticrocksareclassifiedprimarilybytexture,ortheirgrainsize,andtheirsizedistribution,notbytheirmineralcontent.Forexample,sandstoneisatermusedtodescribeanysedimentaryrockcomposedofsedimentsthatrangeinsizefrom0.125millimeterto2millimetersindiameter.Othersedimentaryrocksdifferentiatedbygrainsizeincludeshale,siltstone,claystone,mudstone,cobblestone,andconglomerate.

Becausesedimentaryrocksarelargelyderivedfrommarineandfreshwaterdepositionalenvironments,theserocksoftencontaineitherthefossilizedremainsofplantsandani-malslivingintheaqueousenvironmentsatthetimeortheremainsoflivingthingsthatwerewashedintothedepositionalenvironmentstobecomepreservedintherockrecord.Asanexample,theTwoMedicinerockformationinMontanacon-sistsoffreshwatersedimentsandburiedterrestrialsediments.Paleontologistshaveexcavatedandstudiedmanydinosaurfossilsfromthisformation.

Sedimentsbeingdepositedinriversandonthecontinen-talshelvestodaywillbecometheclasticsedimentaryrocksoftomorrow.Chemicallydepositedsedimentaryrocksarebeingformedtodayincaveswherelimestoneisdissolvedbyground-waterandprecipitatedintheceilingsandfloorsofthesecavesasstalactitesandstalagmites.Evaporitesarecontinuallydepos-itedalongtheshoresoftheMediterraneanSeaandtheGreatSaltLakeinUtah.

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Nonclastic rocks are those formed when minerals precipitate from marine or freshwater. Precipitation occurs when minerals crystallize in a liquid as a result of physical or chemical change, and drop from suspension to the bottom of the water. Evaporites are examples of nonclastic rocks formed when minerals precipitate directly from marine or freshwater solutions. (These are sometimes called chemical precipitates.) Gypsum and halite are examples of evaporites. You can make a nonclastic mineral evaporite by evaporating salt water, leaving the salt crystals.

Metamorphic RocksMetamorphicrocksarethethirdcategoryofrocks.Itseemslogicaltoexplainthemlastbecausetheydevelopfromothersedimentary,igneous,andevenmetamorphicrocks.Meta-morphicrocksresultwhenmineralsinrocksareexposedtoheatandpressure,orhydrothermalsolutionsofmineral-richsteam.Inmostcases,heatandpressurecausethemineralatomsofexistingrockstorearrange,sometimesevenproduc-ingdifferentminerals.Inothercases,newchemicalelementsarebroughtbyveryhotsteammovingthroughexistingrock,whichcanalterthemineralsintherocktoformnewminerals.Hydrothermalsolutionsoftenassociatedwithmetamorphicprocessespenetratesurroundingrocksformingmanyoftheoredepositsfoundintheworld.

Metamorphicrockscanbeformedbycontactwithmagma,byheatandpressureassociatedwithburialofsediments,orbysqueezingforces.Foliated,orlayered,metamorphicrocksgenerallyformfromexistingrocksthathavemanydifferentmineralgrains.Forexample,duringmetamorphism,shale(asedimentaryrockconsistingofverytinygrains,includingboththeprimarysedimentaswellasgrainsofotherminerals)canreformintolargergrainsoftheformerminerals,givingtherockalayeredappearance.Dependingonthedegreeofmetamorphism,shalemaybealteredtoformslate, schist,orgneiss,allofwhichexhibitfoliationbutvaryinggrainsizes.Evenigneousrockscanbealteredbymetamorphicconditions.Graniteisbelievedtoformgneisswhenexposedtometamor-phicconditions.

Nonfoliatedmetamorphicrockscommonlyformfrommonominerals—rockslargelycomposedofonemineral—thatareexposedtometamorphism.Limestone,whichislargelycomposedofcalcite,becomesmarblewhenexposedtometamorphicconditionsofheatandpressure.Sandstone,composedofquartzwithsomefeldspar,willbemetamor-phosedtoformquartzite.

72 GeoloGy

The word metamorphic means to change form. Think of metamorphic rocks as rocks that have changed or formed with heat and pressure from another rock.

Collecting Minerals and RocksMineralsincludeavarietyofmetallic ores,whicharesourcesofimportantmetals,andnonmetallic ores,whicharesourcesofavarietyofproducts,includingbuildingmaterialsandagriculturalsupplements(likefertilizer).Othermineralsandrockshavegreatappealasgemstonesandforornamentalpurposes.Agatesandturquoiseareofinteresttojewelersorrockhoundsjustaslargedepositsofmagnetiteareofinteresttogeologistssearchingforironoretomakesteelorgoodlimestonedepositstomakecrushedrockforhighwaysareofinteresttoaggregateproducers.

Ourancestorssearchedforgooddepositsofobsidian,chert,andflintforarrowheads.ExplorerscomingtotheNewWorldweremotivatedbythedesiretofindgold.TodaygeologistslookforrocksandmineralstounderstandhowEarthcontinuallychangesandaresearchingotherplanetarysurfacestounder-standtheirgeologicprocesses.

Whenyoucollectrockspecimensorstudyrocksandmin-erals,youhavetheopportunitytoholdearthhistoryinyourhandsandtorecognizeearthprocessesatwork.

GeoloGy 73

Shale (sedimentary)Slate (metamorphic)

everyday Uses of RocksSomegeologistsuserocksandmineralstogivethemcluesaboutearthprocessesandaboutthehistoryofEarth.Othergeologistsstudyrocksandmineralstofindnewwaystousethem.

Almosteverycityhasanearbysourceofearthmaterialsusedinmanufacturing,construction,energyproduction,agriculture,andevenrecreation.Arockquarryorsand-and-graveloperationproducesmaterialsforconstructionofroadsorbuildings.Canyouthinkofoneyouhaveseen?CrushedlimestoneisthemostcommonlyminedorquarriedmaterialintheUnitedStates.Millionsoftonsoflimestoneareusedeachyearinthemanufacturingofcementorcrushedrockcalledaggregate.Thisaggregateisusedinroadconcrete,highwayasphalt,andevenloosegravelfordrivewaysandroads.Otherminingoperationsrangefromcoal,gypsum,ore,andsalt,tooilproductionandfertilizermanufacturing.MiningormineralextractionisfoundthroughouttheUnitedStates.

Ifyouexaminewhereyoulive,yourhome,thesidewalksandroads,yourschool,yourplaceofworship,Scoutcamp,sportsfields,evensilverware,nearlyeverythingaroundyouisaproductofminingorcontainsproductsderivedfrommining.

74 GeoloGy

listing of common rocks and minerals, and where to find them

Rock or Mineral Common name Where to obtain Them

Limestone Road aggregate or chat Building supply store

Volcanic scoria or pumice Lava rock Landscaping supplies

Marble Marble chips Landscaping supplies

Use this chart to get started on requirement 3a of the mineral resources option.

Road BuildingRoadbuildingisonewaygeologyaffectsyoueveryday.Firstofall,governmentplannersandconstructioncompaniesemploygeologistsandcivilengineers.Theseprofessionalscantellthemthebestplacestobuildhighways,bypasses,highwayexits,andstreets.Thegeologistorengineerchecksthelocationtobesureitoffersasoundfoundationforaroadbed.

Theselectionofmaterialsisalsoimportantbecausetheremustbeabalancebetweenselectingthebestmaterialsforthejobagainstthecostofpurchasingandtransportingthematerials.Forexample,wemayhaveareadysupplyofrivergravelinthecommunitybutnolimestonetomakecementforconcrete.Itisnotacceptabletobuildahigh-speedinterstatehighwayoutofloosegravel,sowepayahighercosttobringcementtothesitefromhundredsofmilesaway.Oftenitismorecost-efficienttorepairandresurfaceahighwayratherthantobuildanewone.Ifageologisthasaccesstolimestonesuppliesandoilrefinerypetroleum,thegeologistmayrecom-mendresurfacingaconcreteroadwaywithasphalt.

Whatkindsofroadmaterialsareusedinyourarea?Lookatthehighwayclosesttoyourhome,lookatthestreetthatyoutaketoschool,andlookatyourowndrivewayortheparkinglotofanearbybusiness.Whataretheymadeof,andwheredidthematerialsoriginate?

Activity 8: Road Construction Materials in your CommunityNowthatyouunderstandthetypesofrocksthatmakeupEarth,explorehowroadsarebuiltinyourcommunity.Inthisactivityyouwillidentifythethreemostcommonroad-buildingmaterialsinyourcommunity,howtheyareproduced,andhowtheyareusedinroadconstruction.

PRoCeDUReSStep 1—Withthehelpofyourcounselororparent,callorvisitaconstructionengineeroraconcreteorconstructionbusinesslistedintheyellowpages.

Step 2—Takenotesasyouaskwhatthebusinessusesasitsthreemostcommonroadconstructionmaterials.

Step 3—Askhowthesethreematerialsareproducedandhowthesethreematerialsareusedinroadconstruction.

GeoloGy 75

.earth History: The Story Rocks Tell

EarthHistory:TheStoryRocksTellThestoryofgeology,thehistoryofEarth,isdividedintochap-tersmuchlikeabook.Thestoryisfilledwiththemysteryandadventureofwhathappenedtoformerlandsandseas,plantsandanimals.ThismeritbadgepamphletattemptstolookatthedifferentchaptersthattellthestoryofEarth.Afterearningthismeritbadge,youwillhaveabetterunderstandingofEarthandthesourcesofthemineralsandenergyyouuseeachday.

Scientistsusetwobasictechniques—relative datingandabsolute dating—toestimatetheageofarocklayerorafos-sil.Relativedatingisthemostbasictechnique,basedontheobservationthatmostrocksarelaiddowninroughlyhorizontallayers,withtheoldestlayeratthebottomandtheyoungestlayeratthetop.Thisallowsgeologiststosaythatonerocklayerisolderoryoungerthananotherlayer,butitdoesnotidentifytheactualageoftherock.Becausethistechniquetellsonlytherelativeageofarocklayerincomparisontothelayersaboveandbelowit,itiscalledrelative dating.

GeoloGy 77

earth History: The Story Rocks Tell.

Scientistsalsouseabsolute datingtocompareandconfirmtheirrelativedatingmethods.Absolutedatingismeasuredbycalculatingtheradioactive decay,ordegenerationofanelement’satomicstructurethroughtime,astheyphasefromoneelementform(isotope)toanother(likepotassiumtoargon,uraniumtolead,orthedifferentisotopesofcarbon).Usingsophisticatedlaboratoryequipment,scientistscanestimateanelement’shalf-life—thetimeneededforhalfofasampletodecaybylosingatomicparticles.

78 GeoloGy

Using relative dating, the geologist knows rock in layer C is older than layer B but younger than layer D.

HAlF-liFeRadioactivedecayisaprocessinwhichthenucleusofanatomlosessomeatomicparticlesoveraperiodoftime.Asthoseparticlesleavethenucleus,theatomicnumberchangesandtheelementdegradesintoadaughterproduct,sometimescreatingatotallydifferentelement.Forexample,someisotopesofuraniumcandecayintoleadoveraperiodoftime.Somescientistsareconvincedthatmeasuringtheamountofdecaythathasoccurredinarocksamplecangiveusawaytomeasuretime.

Therearefourrelativelyabundantradioactiveisotopesthatoccurinrocks:twoisotopesofuranium(U238andU235),rubidium(Rb87),andpotassium(K40).Wecanmeasuretheratio(therelativeamount)ofdifferentisotopestoothers:uraniumisotopestootheruraniumisotopes,rubidiumtostrontium,uraniumtolead,andpotassiumtoargon.Manygeologistsbelievethisratiowillallowarocktobedatedbasedontheisotope’shalf-life.Imaginea1-gramsampleofuranium238.Intheory,itwouldtake4.5billionyearsforhalf,or0.5grams,ofittodecaytolead206.

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When uranium 238 loses atomic particles and becomes lead 206, it is called radioactive decay. The number 238 is the total protons plus neutrons in the nucleus of this uranium isotope.

Common Radioactive Atomic Half-lives Theory

Atom Billion years

Uranium 238 4.5

Uranium 235 0.7

Rubidium 87 47.0

Potassium 40 1.3

atomic particleS

uranium 238 leaD 206

80 GeoloGy

Geologic Time Scale TheoryC

Precambrian Time

Approximate age of earth: more than 4 billion 600 million years

eraPeriod

and Approximate Duration Characteristic life

ouarternary(1 million yrS)recent pleiStocene

tertiary(64 million yrS.)pliocenemioceneoliGoceneeocenepaliocene

cretaceouS(70 million yrS.)

JuraSSic(45 million yrS.)

triaSSic(50 million yrS.)

permian(55 million yrS.)

pennSylvanian(30 million yrS.)

miSSiSSippian(35 million yrS.)

Devonian(55 million yrS.)

Silurian(20 million yrS.)

orDovician(75 million yrS.)

cambrian(100 million yrS.)

proterozoic era(800 million yrS.)

archeozoic era(3.2 billion yrS.)

AgeologicmapshowsthecommonagesandtypesofrocksonEarth’ssurface.Askyourcounselortoshowyouageologicmapoftheareainwhichyouliveand,usingthemaplegendanddescriptions,discusshowtoestimatetheageofthesurfacerocksinyourarea.

Fossils Give Clues to the PastHaveyoueverwonderedwhyweareallsointerestedinfossils?Isitbecausebig,scarycreatureslikeTyrannosaurus rexorsaber-toothedtigersfascinateus?That’scertainlypartofit,butmostfossilsarenottheremainsofbig,scarycreatures.Muchofourfascinationwithfossilsisbecausetheyaretheclosestthingspeoplehavetoatimemachine,awaytogobackintoprehistorictimesandtoseeEarth’splantsandanimalsoflongago.Thestudyoffossilsiscalledpaleontology,andthegeolo-gistwhostudiesfossilsisapaleontologist.Thepaleontologistreconstructsthepastbycombiningtheknowledgeofmodernanimalsandplantswithwhatisknownabouttheremainsofancientanimalsandplantsfromfossils.

GeoloGy 81

Geologic time is

organized into

eras. Each era

represents a time

during which

certain lifestyles

dominated Earth.

Eras cover long

intervals of time,

so geologists find

it useful to further

divide the eras

into shorter

time intervals

called periods.

Forexample,todaysharksliveintheocean.Sharkteetharedistinctive,notlikeyourteethortheteethofothermam-mals.Whenpaleontologistsfindasharktoothinarocklayer,theyknowthattherocklayerwasdepositedonanoceanfloor.Aspaleontologistsstudytherocklayerthatheldthesharktooth,theymayfindmorefossilsandgatherothergeologicinformation.Togetherthefossilsandotherinformationallowthepaleontologiststopiecetogetheranideaoftheoceanthesharklivedin.Alsobasedonthesizeofthefossiltoothcomparedtotoday’ssharkteeth,thepaleontologistcancloselyestimatetheshark’ssize.

Whatotheranimalslivedthere?Wasthewaterdeeporshallow?Wasthebottomsandyorwasitahardreefmadeofcoral?Ifthiswastheocean,wherewastheland?Youcan’tgobackintime,butyoucanuseyourknowledgeofmodernoceansandmodernlife,withyourknowledgeoffossils,tocompareancienttimeswiththepresent.

Whatmakesananimalorplantturnintoafossil?Ifyouareatsummercampandaraccoondiesnearyourtent,itprobablywon’tturnintoafossil.Asitliesontheground,vultures,beetles,flies,andotherscavengerseatit.Eventhebonesaredestroyed.Bythetimeyoureturntocampthenextsummer,notraceofthatraccoonwillremain.Itwillneverbecomeafossil.

Thekeyforanyanimalorplanttobecomeafossilisthatitmustbeburiedsoonafterdeath.Ifaraccoonfallsintoastreamorriver,theriversandsormudwillburyitquickly.Evenifthesofttissuesoftheanimalaredecayed,itsbonesmaybepreservedandthelayersofsandandmudcoveringthebonesprotectitfrombeingdestroyed.Unfortunately,animalsthatliveonlandhaveapoorchanceofbecomingfossils.Thereareveryfewsituationswheretheyarequicklyburied.Thereareplaceswhereanimalshavebeenburiedinariver,asatDinosaurNationalMonumentinUtah,orinatarpit,asatLaBreaTarPitsinLosAngeles.However,theseplacesarenotcommon.

82 GeoloGy

Fossils act like

time machines

for geologists,

allowing them a

peek into the past.

Only a fraction of plants and animals die and fall in a place with the right conditions for fossils to form. Yet even with the low chance of becoming a fossil there are billions of fossils in the world, from big dinosaur bones to tiny microfossils.

Theshellsofclams,snails,andothershell-bearinganimalscanbepreservedasfossils.Plantsandevensoft-bodiedwormscanformimpressionsinsoftmudthatpreservetheshapeoftheseorganismsafterthemudturnstorock.Sometimes,aftertheshellhasbeenburiedinsoftmud,itwilldissolve,leavingtheshapeoftheshellpreservedasamoldintherock.

Measuring Time Using FossilsManygeologistscommonlyspeakoftheageofarockorfos-silinmillionsorevenbillionsofyears.Peoplehavealifespanofonlyabout60to100years,soamillionorabillionyearsisalmostimpossibletoimagine.Howcanyoudeterminetheageofsomethingthatold?

Geologistsrefertotheabundant fossil recordasthattimewhennumerousanddifferentlifeformsappearedonEarthatthesametime.BeforetheCambrianPeriod,mostlifeformsweresingle-celledorganismslikeamoeba,bacteria,orplankton.AtthebeginningoftheCambrian(beginningofthePaleozoicEra),manylifeformsappearedintheworldoceanandmostofthemwerecomplex,multicelledorganisms(animalsandplantsthatdevelopedseveraltypesofspecializedcellswithintheirbodies,eachperformingaspecializedfunction).Theseorganismswerenolongerlivingonphotosynthesis(likeaplant)orbyabsorbingnutrientsfromsurroundingwater(likeanamoebaorbacteria).Theseanimalsandplantsweredevelopingandgrowinglarger.

Onceburied,thegrainsofsedimentcovertheplantoranimalandaccumulate.Iftheplantoranimalhas“hardparts”likeashellorwoodytrunk,theycansupporttheweightofoverlyingsediments.Thenthemudwillcreateamoldaroundthefossil.Asthesedimentshardenintorock,themoldedimpressionalsohardensanditsoutlinemaystillbeseen,evenifthefossilisdissolvedaway.

Sometimesyoucanfindananimalfossilthathasunder-gonereplacementofitsoriginalshellmaterialwithanew,sec-ondarymineral.Thisoccurslongafterburialwhentheoriginalshellmaterialisslowlydissolvedawaybygroundwater.Thenonemoleculeatatimeseepsintofillthevoid.

Relativedatingismostcommonforfossils.Afterexamin-ingthousandsofdifferentfossilsandcomparingtherocksinwhichtheyareformedwithrocksdatedbyradioactivemeans,paleontologistshavedeterminedanagerangeformostfossilsandtherocksthatcontainthem.

GeoloGy 83

Ocean animals

like clams, snails,

and corals have

a greater chance

of becoming

fossils than

land animals,

partly because

sediments quickly

bury them on

the ocean floor,

but also because

they have

hard shells.

life Through Time in the Fossil RecordThefossilrecordsuggeststhatlifehaschangedthroughtime.Youmayfindthatnoneofthespeciesinthefossilsyoucollectarealivetoday.Manyplantsandanimalsmayhavedevelopedandthrivedunderaspecificsetofenvironmentalconditions.Thissetofconditionsisapaleoenvironment.Whenconditionschangetheplantoranimalisnolongerabletocompeteforfoodanddiesoff.Iftheconditionschangeacrossawideenoughareatheplantoranimalmaybecomeextinct.Onecircumstancethatcouldhavecausedextinctionsoccurredduringatimewhenfreezingtemperatureskilledplants.Whenplantsdie,plant-eatinganimalsstarveandalsodie.TheplantandanimalspeciesalivetodayareonlyafractionofallthespeciesthathavebeenaliveduringEarth’shistory.

84 GeoloGy

Make a fossil with plaster of paris. Find an animal footprint in soft mud. Pour plaster of paris over the footprint. When it hardens lift your “fossil” out of the mud. This may be a part of a Scout nature study. Make a plant fossil by pouring plaster of paris in a disposable tray, like an aluminum baking tin, and then press a fern or other leaf into it.

Fossilrecordssuggestthatduringcertainrelativelyshorttimeperiodsmassiveextinctionsoccurred,calledextinctionevents.Duringtheseevents,notonlycouldindividualspe-ciesbecomeextinct,butevenentireecosystems.TwomajorextinctioneventscouldhaveoccurredsincethebeginningofthePaleozoicEra.OnemighthaveoccurredattheendofthePaleozoic,thesecondattheendoftheMesozoicEra.

Ofcourse,notallspeciesofplantsandanimalsdiedoutattheendofthePaleozoic.SharksoriginallyappearedduringthePaleozoicEraandhaveremainedessentiallyunchangedsincethen.Therecordshowsmanynewspeciesdevelopedduringthenextera,theMesozoic.TheMesozoicEraismostcommonlythoughtofastheageofdinosaurs,althoughmanyotherplantsandanimalswerepresentduringthattime.

GeoloGy 85

The U.S. Fish and Wildlife Service monitors species populations to raise aware-ness and ensure protection from extinction. Identify three endangered or threat-ened plants or animals. You can find this information at the public library, or on the Internet with your par-ent’s permission. See the resources section.

ThefinaleraistheCenozoicEra,whichstartedattheendoftheMesozoicandcontinuesthroughtoday.ThewordCenozoicmeansrecentlife.Thelast1.5millionyearsoftheCenozoicEraincludeadistinctivepaleoenvironmentalfeature,knownastheIce Age.ScientistsbelieveitwasatimewhenperiodsofextremelycoldclimateallowedthewidespreaddevelopmentofglaciersintheNorthernHemisphere(thenorthhalfoftheplanetEarth).InNorthAmerica,widespreadsheetsofice,measuringhundredsorthousandsofmilesacross,spreadsouthwardfromtheNorthPoleandfilledthecontinentfromtheAppalachianMountainsintheeasttotheRockyMountainsinthewest.ThesesheetsoficeextendedasfarsouthasKansasandtheicemeasuredmorethanamilethickinsomeplaces.Seethesectioninthispamphletaboutglaciers.

Accordingtotheory,duringthisIceAge,manyplantsandanimalsadaptedtothenewlivingconditions.MammothsandmastadonswerecommoninNorthAmericaandmayhavebeenhuntedforfood.Theclimatesouthoftheicesheetswasrainy,andinsectsthrived.Batsandbirdsthrivedbyeatingtheabundanceofinsects,andmayhavegrownmuchlargerthantheyaretoday.

interpreting the Past With FossilsEveryanimalandplantspeciestendstobefoundwithinthehabitatinwhichtheyarebestadaptedtosurvive.Environ-mentalconditionsvaryfromonehabitattothenext.Forexam-ple,theforestfloorofatropicalrainforestisusuallyhumidfromfrequentrainandhaslittlesunlight.Manysmallerplantsgrowthicklyandcovertheforestfloor.Aplantadaptedtosurvive

86 GeoloGy

The fossil record suggests, despite what many people think, that all dinosaurs did not live at the same time. The familiar Apatosaurus (formerly called Brontosaurus) lived in the Late Jurassic period, which many scientists believe ended about 140 million years ago. Tyrannosaurus rex lived during the Late Cretaceous period, which these scientists theorize ended about 70 million years ago. Accordingly, they believe the last of the tyrannosaurs lived about 70 million years after the extinction of Apatosaurus. In theory, there are as many years separating Apatosaurus from Tyrannosaurus as the number of years between Tyrannosaurus and you.

GeoloGy 87

onarainforestfloormightnotbeabletosurviveatallinanopenfieldwhereitishotanddry,orinadesert.Likewise,aplantfromasunnyfieldprobablycouldnotsurvivelonginthemoistshadyflooroftherainforest.Theamountofsunlightandtheamountofmoisturelimitwhereparticularplantscansurvive.

Ananimallivingintheoceanalsomustbeadaptedtoitsenvironmentalconditions.Onemajorenvironmentalfactorisoceansalinity,theamountofsaltdissolvedinthewater.Farfromland,salinityremainsconstantandfishandotheranimalshaveadaptedtothisopen marineenvironment.Nearshore,riverspourintotheocean,bringingfreshwater.Thisfreshwaterreducestheoceansalinityatthemouthoftheriver.Atthispointsalinityislessthannormaloceansalinity.Thiswateriscalledbrackish.Animalslivinginbrackishwaterareabletoadapttochangesinsalinity.Manyfishthatsurviveinbrackishwatercannotsurviveinthehighersalinityoftheopenoceanorinafreshwaterriverorlake.

Intheocean,scientistshaveobservedthatdifferentmarineanimalsliveinparticularenvironments.Geologistsstudyfossilsofthesemarineanimalsandtheirpaleoenvironment.Knowingthisinformationaboutpaleoenvironmentshelpsgeologiststopinpointareasofpossiblemineralvalue.

Marine Animal environmentsWhereananimallivestellsushowiteatsandsurvives.Pelagicanimalsarethosethateitherswimordriftinthewaternearthesurface.Sincepelagicanimalsswimorfloat,theymusteatthingsthatswimorfloat.Someplantsarepelagicandlivenearthesurfacewheretheycancatchthesunlight.

Benthicanimalsarethosethatliveonthebottomoftheocean.Abenthicplant,likeallplants,requiressunlightforphotosynthesis.Sincesunlightonlyfiltersthroughwatertoalimiteddepth,benthicplantsonlyliveinshallowwater.Abenthicanimalcanstayinoneplaceandwaitforfoodtofloatpast,whichaclamwoulddo.Oritcanlivelikeastarfishcrawlingalongslowlyeatingotherbenthicanimals.Becausetheseanimalswilldieifwashedouttoseainastormcurrent,mosthaveadaptedsomesortofanchortohelpthemstayinplace.

The most common

benthic animal are

the corals, which

build rigid skele-

tons in community

structures called

coral reefs.

Littoralanimalslivealongtheshorelineboundedbythelevelsofhighandlowtide.Thisiscalledtheintertidalzone.Tidepoolsarelittoralenvironmentswheretheyareunderwaterandoutofwaterpartofthetime.

Notallanimalsthatliveinwaterliveintheocean.Thoselivinginriversliveinafluvialenvironment,andanimalslivinginlakesliveinalacustrineenvironment.

Becauseanimalstendtoliveinveryspecificenvironments,theirfossilremainsgiveusalotofinformationaboutthehistoryofthearea.Acoralreeftendstocreateabarrierbetweentheshoreandtheopensea,sofrequentlyaquietwaterlagoonislocatedbetweenthereefandtheshore.Knowingthisgeologistscanpredictinwhichdirectionrockswillbedepositedintheopenocean,versusrocksonshore.Thiswillenablegeologiststodrawapaleogeographic map,oramapshowingtheancientgeographyatthetimeofsedimentdeposition.

Field Trips Are for learning About Geology Geologistslovetotakefieldtripstoseerockcollections.Amuseumoruniversitygeologydepartmentisthebestplacetoseehowprofessionalgeologistsorganizeandcategorizetheircollections,especiallywhenthesecollectionsareusedtoeducatestudentsorthegeneralpublic.

Tocompletetherequirementsfortheearthhistoryoption,eachScoutisencouragedtovisitamuseumoruniversitygeologydepartment.Remembertocallaheadandmakeanappointmentwithacuratororprofessorsothatpersoncansetasideenoughtimetoproperlyshowthefossilandmineralcollections.Thepeoplewhoworkinsuchplacesenjoyhavingthepublicvisitandmostwillhappilytaketimeforyou.Besuretoaskquestionsandhavethemshowyouhowtheycleanandprepareafreshlydiscoveredfossilfordisplay.

Ifthereisnotamuseumoruniversitydepartmentnearby,yourcounselormaybeabletoprovideaddressesoflocalbuild-ingsthatusedfossiliferousrocksasbuildingstones.Visitthesebuildingsandtreatthemlikefossildigsites.

1.Sketchthebuildingfossilsinyournotebookorphotographthemandtapephotosintoyournotebookwithwrittendescriptionsofthefossilandanythingelseyouobserve.

88 GeoloGy

Suppose you

discover fossils

of marine animals

that lived in the

tropical ocean

waters near your

home. The ocean

may have extended

over the land

where you now

live. This suggests

that when the

fossilized animals

were alive, your

home’s climate

was warmer.

2.Observethetypeofrockthatcontainsthefossils(isitsand-stoneorlimestone),andobservewhethertherockgrainsareveryfineormorecoarse.Finergrainshelppreservefossilsingreaterdetail.Canyoudescribethepaleoenvironmentofdepositionfromlookingattheserocks?Rememberthatfinergrainedsedimentsoccurincalmerwater,whereascoarsersedimentsoccurwherethereisacurrent,asinastreamorbeach.Alsorememberthatcertainkindsofplantsandanimalsliveincertainkindsofpaleoenvironmentsandtheirverypresenceisacluetotheancientenvironment.Writeyourthoughtsinyournotebookanddiscussyourobserva-tionswithyourcounselor.

GeoloGy 89

If you happen to be on vacation or away from home for some reason, you may discover a rock outcropping worth exploring. Take notes, photographs, and sketches of what you see there. When you return home, you and your buddy can meet with your counselor and discuss what you found at the outcrop.

If a visitation is not practical for you, create a display or presenta-tion on your state fossil instead. Your research at the library and online (with your parent’s permission) will pay off with an amazing presentation. Remember, if your state does not have a state fossil, you may select a state fossil from a neighboring state.

.Careers in Geology

CareersinGeologyEvenifyouarenotinterestedinacareeringeology,itisgoodtolearnmoreaboutourEarth.KnowledgeofgeologymakesEarthevenmoreinteresting.Awalkordriveismorefunifyouknowwhyandhowthehillsandvalleysformed,howthewavesonabeachsortanddistributesand,howsandsomedaywillbeasolidrockandcarryoil,gas,andwater,howpartofthelandisalwaysonitswaytothesea,andwherethemineralscomefromthatareusedtomakethethingsyouuseeveryday.

Geologyisawidefieldwithmanycareerchoices.Hydro-geologistshelpfindwaterundergroundandcanplanhowmuchtousesoyouwillnotrunout.Geologicalengineersadvisewheretobuildadam,wherebridgeabutmentsandpiersmaybebuiltsafely,wherebuildingswillhavesolidfoundations,orwheretunnelscanbebuiltwithoutcollapsing.

Manygeologistsareinvolvedintheexplorationofand/ortheproductionofnaturalresources,likeoilandgas,coal,ironore,copper,gold,andcountlessotherminerals.

GeoloGy 91

To learn more

about geology

take an earth

science course

in high school,

or two or more

college courses

in geology.

Careers in Geology.

Aprofessionalgeologistmustearnatleastafour-yearcollegedegree(bachelor’sdegree)ingeology,geophysics,environmentalgeology,orgeologicalengineering.Inmanyfieldsamaster’sdegree(twoyearsbeyondabachelor’sdegree)maybenecessary.Toteachatacollegeoruniversity,ortodoresearch,adoctorateisrequired(threetosevenyearsbeyondabachelor’sdegree).

Asidefromgeologycourses,allgeologistsshouldtakefundamentalsciencecoursessuchaschemistryandphysics,andalsomathematics.Somefieldswillrequirespecializedcourses.Writingskillsarealwaysimportant,asgeologistsmustwritereportsabouttheirdiscoveriesandtellotherswhattheyhavefound.Virtuallyallgeologistsusecomputersextensivelyintheirwork.

Geologyisfun.Geologistsenjoytheirprofessionandlikethechallengeandadventure.Geologistswerethefirstenviron-mentalists.Theyenjoyworkingoutdoorsandinout-of-the-wayplacesthatarehardtoreachandwhereitisdifficulttolive.Geologistsliketosolvepuzzlesandliketograpplewithgeo-logicalproblems,usingevidenceyoumay—ormaynot—beabletosee.

92 GeoloGy

For more information on careers in geology, or to find what schools offer geology or geology related degrees, contact the American Geological Institute. Many professional societies also have career infor-mation. See the resources section at the end of this pamphlet.

.Careers in Geology

GeoloGy 93

Geology Resources.

Scouting literatureArchaeology, Chemistry, Collections, Drafting, Energy, Engineering, Environmental Science, Landscape Architecture, Nuclear Science, Oceanography, Orienteering, Soil and Water Conservation, SurveyingandWeathermeritbadgepamphlets

Altman,LindaJacobs.The California Gold Rush in American History.EnslowPublishersInc.,1997.

Dixon,Dougal.The Practical Geologist.Simon&SchusterInc.,1992.

Erickson,Jon.Historical Geology.FactsOnFileInc.2002.

Gaines,R.,H.Skinner,E.Foord,B.Mason,andA.Rosenzweig.Dana’s New Mineralogy.Wiley-Interscience,1997.

Hyne,NormanJ.,Ph.D.Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production.PennWellCorp.,2001.

Johnson,Carl.Fire on the Mountain.ChronicleBooks,1994.

Lamb,Simon,andDavidSington.Earth Story: The Forces That Have Shaped Our Planet.PrincetonUniversityPress,1998.

Lambert,David,andtheDiagramGroup.The Field Guide to Geology.FactsOnFile,1998.

Pough,FrederickH.Rocks and Minerals.HoughtonMifflinCo.,1996.

Redfern,Martin.Planet Earth.KingfisherPublications,1999.

Thompson,GrahamR.,Ph.D.,andJonathanTurk,Ph.D.Introduction to Physical Geology.HarcourtBraceCollegePublishers,1998.

VanCleave,Janice.Rocks and Minerals.JohnWiley&SonsInc.,1996.

94 GeoloGy

Visit the Boy Scouts of America’s official retail Web site at http://www.scoutstuff.org for a complete listing of all merit badge pamphlets and other helpful Scouting materi-als and supplies.

GeologyResources

.Geology Resources

organizations and Web SitesAmerican Association of Petroleum Geologists1444SouthBoulderTulsa,OK74119Telephone:800-364-2274Website:http://www.aapg.org

American Geological institute 4220KingSt.Alexandria,VA22302-1502Telephone:703-379-2480Website:http://www.agiweb.org

American Petroleum institute1220LSt.NWWashington,DC20005-4070Telephone:202-682-8000Website:http://www.api.org

The Geological Society of AmericaP.O.Box9140Boulder,CO80301-9140Telephone:303-357-1000Website:http://www.geosociety.org

Paleontological Research institute1259TrumansburgRoadIthaca,NY14850Telephone:607-273-6623Website:http://www.priweb.org

Society of exploration Geophysicists8801SouthYaleAve.Tulsa,OK74137-3575Website:http://www.seg.orgTelephone:918-497-5500

U.S. Geological SurveyWebsite:http://www.usgs.gov

AcknowledgmentsTheBoyScoutsofAmericathankstheE.F.ReidScoutingFundoftheAmericanAssociationofPetroleumGeologistsFoundationforitsworkinpromotingthescienceofgeologyinScouting.Inparticular,theBSAthanksRonaldHart(teamleader),RobertBaxter,RichardErickson,ShermanLundy,John“Jack”Thomas,andWilliamUnderwoodfortheirtimeandexpertiseinwritingthiseditionoftheGeologymeritbadgepamphlet,aswellasthe2009revision.

SpecialthankstoMichaelJackson,TonyKolodziej,andRobertSilvafortheirassistanceinreviewingmaterialsandtotheAmericanAssociationofPetroleumGeologistsandtheSocietyofExplorationGeophysicistsfortheirassistance.

WeappreciatetheQuicklistConsultingCommitteeoftheAssociationforLibraryServicetoChildren,adivisionoftheAmericanLibraryAssociation,foritsassistancewithupdatingtheresourcessectionofthismeritbadgepamphlet.

GeoloGy 95

Geology Resources.

Photo and illustration Credits

HAAPMediaLtd.,courtesy—pages59and69

MiguelHernandezIII,courtesy—page17

NASA,courtesy—pages37and39

Photos.com—cover(all except patch);pages6–10(all),21(top),24(center),32,33(top),38(both),40–41(both),45(top), 46–47(both),57,64(salt, mica, quartz),65(quartz),70,73(both),76–77(all),85(all),87,and91

TheWildernessSociety/KevinWalker,courtesy—page16

U.S.GeologicalSurvey,courtesy—pages24(top, bottom),50(top),and93(top left, right center)

U.S.GeologicalSurvey/J.D.Griggs,courtesy—page90

U.S.GeologicalSurvey/D.P.Hill,courtesy—page66

U.S.GeologicalSurvey/R.McGimsey,courtesy—page93(left center, top right, bottom right)

Wikipedia.org,courtesy—pages64(calcite),65(galena, pyrite),and71

AllotherphotosnotmentionedabovearethepropertyoforareprotectedbytheBoyScoutsofAmerica.

JohnMcDearmon—allillustrationsonpages12–15,18,21,25–31,36,42–45,48–49,60,65,67–68,and78–80.

BrianPayne—page84

RandyPiland—pages55,56,61,81,and89

96 GeoloGy

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