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.
