geology - troop5.files.wordpress.com · 1. list the top five earth resources used to generate...
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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.
35904ISBN 978-0-8395-3284-2©2005 Boy Scouts of America2009 Revision of the 2005 Edition
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.
3. DoONEofthefollowing:
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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5. DoONEofthefollowing:
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.
GeoloGy 11
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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Folds
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
GeoloGy 17
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.
.Streams Carving earth’s Surface
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
Streams Carving earth’s Surface.
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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1
4
.Streams Carving earth’s Surface
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.
Streams Carving earth’s Surface.
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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.
.Streams Carving earth’s Surface
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
Streams Carving earth’s Surface.
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
.Streams Carving earth’s Surface
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
Streams Carving earth’s Surface.
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
.Streams Carving earth’s Surface
GeoloGy 29
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
Streams Carving earth’s Surface.
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
.Streams Carving earth’s Surface
thedistanceonthemapbetweenthepointswitharulerandconvertittofeetormilesusingthescaleonthemap.Ifthedistanceisinmiles,multiplyitby5,280toconvertittofeet.
Step 3—Readtheelevationofthestreamatthebeginningandendingpointsyouselectedinthelaststep.Oftennotallcontourlinesarelabeled,buttheintervalisthechangeinelevationbetweeneachcontourline.Usethisinformationtofindtheelevationofthecontourlinesthatcrossthestream.
Step 4—Calculatethestreamgradient—theratioofelevationchangetodistance.Streamgradientsareexpressedinratioformsotheycanbereducedtothelowestcommondenominator.
Step 5—Repeatsteps1through4withtheremainingthreemaps.
GeoloGy 31
Streams Carving earth’s Surface.
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
.Streams Carving earth’s Surface
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
Streams Carving earth’s Surface.
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
.Streams Carving earth’s Surface
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
Streams Carving earth’s Surface.
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.
.energy From our earth
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
coal
otherFuel oil
hyDroelectric
natural GaS
nuclear
.energy From our earth
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.
rock
pore
pore
pore
pore
pore
pore
rock
rock
rock
rock
energy From our earth.
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
.energy From our earth
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
Steam
Steamelectrical
power tranSmiSSion
GeneratorturbineconDenSor
pump
coolinG tower
nuclear core
boilinG water
control roDS
water
Creating nuclear energy
energy From our earth.
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
.energy From our earth
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.
energy From our earth.
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
.energy From our earth
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.
energy From our earth.
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.
.energy From our earth
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
energy From our earth.
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
.energy From our earth
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
energy From our earth.
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.
.energy From our earth
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
energy From our earth.
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
.Minerals: earth’s Treasures
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
Minerals: earth’s Treasures.
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
.Minerals: earth’s Treasures
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.
Minerals: earth’s Treasures.
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
Salt
.Minerals: earth’s Treasures
Crystal Form Whenamineralsolutionisallowedtocoolslowly,crystalscangrow.Amineraltakesacrystalformifitisallowedtogrowwithoutconstraint,butthelackofacrystalshapedoesnotruleoutanyparticularmineral.Geologistscanidentifycertainmineralsbytheircharacteristiccrystalshape.
Forexample,quartzmayforminavolcanicsteamvent,wherethequartzisdepositedonemoleculeatatimeonthesidesoftheventopening,allowingtimeforthequartztoformintocrystals.Graniteformingundergroundcontainsquartz,butthisquartziscrowdedbyothermineralsanddoesnotformlargercrystals.
GeoloGy 65
Galena HalitePyrite
Galena Quartz Pyrite
QuartzQuartz orthoclase
Minerals: earth’s Treasures.
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.
.Minerals: earth’s Treasures
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)
cruSt
0
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
.Minerals: earth’s Treasures
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.
GeoloGy 69
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.
Minerals: earth’s Treasures.
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
.Minerals: earth’s Treasures
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.
GeoloGy 71
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.
Minerals: earth’s Treasures.
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.
.Minerals: earth’s Treasures
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)
Minerals: earth’s Treasures.
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.
.Minerals: earth’s Treasures
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.
.earth History: The Story Rocks Tell
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.
GeoloGy 79
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
earth History: The Story Rocks Tell.
80 GeoloGy
Geologic Time Scale TheoryC
eno
zoic
Mes
ozo
icPa
leo
zoic
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.)
.earth History: The Story Rocks Tell
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.
earth History: The Story Rocks Tell.
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.
.earth History: The Story Rocks Tell
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.
earth History: The Story Rocks Tell.
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.
.earth History: The Story Rocks Tell
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.
earth History: The Story Rocks Tell.
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
.earth History: The Story Rocks Tell
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.
.earth History: The Story Rocks Tell
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
Books
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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