Name_____________________________________________________ Date___________GEOL1:physicalgeology

EvaluatingthelinesofevidenceforplatetectonicsGoodsciencemeansthatwedon’tmindlesslyacceptideasastrue—wecriticallyevaluatethoseideas.Asyouknow,thatcriticalevaluationinvolvesmakingobservationsandinterpretations.Platetectonics,whichyouwillinvestigateindetailthisweek,istheacceptedideainthescientificcommunityabouthowtheEarthworks.Itexplainsgeologicphenomenasuchasearthquakes,volcaniceruptions,andmountainbuilding.However,ittookdecadesofcarefulobservations,interpretations,arguing,modifyingideas,etc.todevelopthisidea.Likeanygoodgeologistwoulddo,Iwantyoutospendsometimeevaluatingthelinesofevidencethatwereusedtodeveloptheideathatwenowknowasplatetectonics.I.Evidenceforcontinentaldrift(1)Briefly,whatdoes“continentaldrift”mean,andwhenwasthisideaproposed?Inpreparationfortoday’sclass,youshouldhavedonesomereadingononeofthefollowinglinesofevidencethatwasusedtosupportcontinentaldrift:

• Continentalshapesandassociatedgeologicfeatures• Distributionoffossils• Glacialdepositsinunusualplaces

Whichlineofevidencedidyoupreparefortoday?________________________________________________(2)Usingyourknowledgeandyourgroupmembers’knowledge,Iwantyoutobriefly:

• describeeachlineofevidence(that’stheobservation)• explainhoweachlineofevidencesupportstheideaofcontinentaldrift(that’sthe

interpretation)I’vegivenyouspacetodothisonthebacksideofthispage.Someissuestothinkabout:1)WhatdidWegenerobserveabouttheshapesofcontinentalcoastlines?GiveoneexampleofapairofcontinentsthatwereusedtosupporttheexistenceofPangaea.2)Whatisafossil?WhatwasobservedaboutthelocationoffossilsthatsupportedtheexistenceofPangaea?Whattypesoffossilswereobserved?3)Howdidcharacteristics(location,chemicalcomposition,age)ofcertainrocksandmountainrangessupporttheexistenceofPangaea?4)Whatisaglacier?Whichenvironmentalconditionsarenecessaryforglacierstoform?Whatisaglacialdeposit?Whatdoesthepresenceofglacialdepositstellscientistsaboutthepastclimateinaparticulararea?WherewereglacialdepositsobservedthatsupportedtheexistenceofPangaea?HowdidglacialdepositsprovideevidencethatPangaeahadexisted?

Evidence Observation(explanationofwhatwasobserved)

Interpretation(howtheseobservationssupporttheideaofcontinentaldrift)

Continentalshapesandassociatedgeologicfeatures

Distributionoffossils

Glacialdepositsinunusualplaces

II.EvidenceforplatetectonicsAswewilldiscussinclassnextclass,platetectonicsisamodifiedversionofcontinentaldrift.Scientistsmadeseveralobservationsthatprovidedevidenceforplatetectonics.Inpreparationfortoday’sclass,youshouldhavedonesomereadingononeofthefollowinglinesofevidencethatwasusedtosupportcontinentaldrift:

• Ageoftheseafloor• Sedimentthicknessontheoceanfloor• Shapeoftheoceanfloor

Whichlineofevidencedidyoupreparefortoday?________________________________________________Tofacilitateyourunderstandingofthesethreelinesofevidence,Ihaveprovidedyouwithfourworldmaps.Thered,orange,andyellowcolormapillustratestheageoftheseafloor.Thesecondmapillustratessedimentthicknessontheoceanfloor.Thetopblackandwhitemapillustratesthelocationofmid‐oceanridges.Thelowerblackandwhitemapillustrates,amongotherthings,thelocationofdeep‐seatrenches.Usetheappropriatemap(s)whenthinkingaboutthesequestions.Itwouldalsobeagreatideatolookforpatternssharedbetweenthemaps!!Shapeoftheoceanfloor(3)Istheoceanfloorcompletelyflat?Ifnot,listfourphysicalfeaturesfoundontheoceanfloorandbrieflydescribewhateachlookslike.Youmaymakesketchesifthathelpsyou.

Ageoftheseafloor(4)Whichrockistheseafloor(oceaniccrust)madeof?(5)Theapproximateageoftheoldestoceaniccrustis___________________________________________.(6)Theapproximateageoftheyoungestoceaniccrustis_______________________________________.(7)Generally,whereistheoldestoceaniccrustfound?Doesthiscorrespondtoanyofthephysicalfeaturesthatyouidentifiedinquestion3?Ifso,which?(8)Generally,whereistheyoungestoceaniccrustfound?Doesthiscorrespondtoanyofthephysicalfeaturesthatyouidentifiedinquestion3?Ifso,which?

Sedimentthicknessontheoceanfloor(9)Whatisthedifferencebetweenoceaniccrustandsediment?(10)Wheredoessedimentonthebottomoftheoceancomefrom?(11)Generally,wherearethethickestlayersofmarinesedimentfound?Doesthiscorrespondtoanyofthephysicalfeaturesthatyouidentifiedinquestion3?Ifso,which?(12)Generally,wherearethethinnestlayersofmarinesedimentfound?Doesthiscorrespondtoanyofthephysicalfeaturesthatyouidentifiedinquestion3?Ifso,which?

(13)Finally,Iwantyoutousethedatathatyoucompiledinquestions3‐12andbriefly:• Summarizeeachlineofevidence(thesearetheobservations)• ***comeupwithahypothesisofwhyeachlineofevidenceexists.Notethattheseare

justhypotheses—it’sOKtobeincorrect.Wewillevaluateyourhypothesesnextclass.

Example:observation—thethickestlayersofsedimentarelocated______. Hypothesis—thethickestlayersofsedimentarelocatedthere because_____________________________________________.

Evidence Observation(whatdidyounotice?Were

thereanypatterns?)Hypothesis(whydotheseobservations/patternsexist?)

Shapeoftheoceanfloor

Ageofseafloor

Sedimentthicknessonoceanfloor

Marinesedimentthickness—datacourtesyofNOAA

Above:diagramillustratingthelocationofmid­oceanridges.

CourtesyofSanJoseStateUniversity(http://oceansjsu.com/105d/exped_boundaries/2.html)

Above:Thismapillustratesthelocationofdifferenttypesofplateboundaries,whichwehaven’ttalkedaboutinclassyet.Thepurposeofyoulookingatthismapistonoticethelocationsofdeepseatrenches,

whichareillustratedusingthe“teeth”pattern.IgnoretheX,Y,andZ.ImagecourtesyofPimaCommunityCollege.