Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Sedimentary Rock
Document related concepts
Transcript
Name:_______________________________ SedimentaryRock Directions:Read,highlight,answerquestionsinschoology. Overmillionsofyears,rocksareweathereddownbyforcesofwindandwater.Fineparticlesofdirtbeginto coverthelandscape.Often,thesesmallrockparticlesendupbeingsuspendedinwater,andfindtheirwayto thebottomoflakes,streams,andtheocean. Slowly,thelayerofsedimentonthebottomoflakes,andespeciallyonthebottomoftheoceangrows deeperanddeeper.Intheoceanitcanreachdepthsofthousandsoffeet.Theweightofallthesediment becomesreallylarge,pushingdownonlowerlayersofsedimentwithtremendousforce.Anumberof mineralsmixedinwiththesedimentactslikecement,holdingthesedimenttogether,causingittoform sedimentaryrock. Sedimentaryrocksformlessthan10percentoftherocksonEarthcoveringothertypesofrockslikeathin coatofpaint.EventhoughtheyareonlyatinypercentageoftherocksonEarth,theytellusalotaboutthe historyoflifeonearthbecausesedimentaryrocksaretheonlytypeofrockthatcanholdfossils,andtheyare formedinlayerswiththeoldestrocksonthebottomandthenewestrocksonthetop(calledstratification). Butwhywouldsedimentaryholdfossilsbutnotmetamorphicorigneous?Thereasonisprettysimple,heat. Igneouswouldburnanylivingthingup(thinklavameetsanythingthatburns)whilemetamorphicisunder hightemperatureandpressure.Itispossiblesometimesformetamorphictostillhavealittlebitoffossilleft ifitformsfromsedimentary,butthatdoesn’thappenveryoften. Therearemanykindsofsedimentaryrocks.Scientistsdividethetypesofsedimentaryrocksintothreekinds, clastic,chemical,andorganic. Erosion Sohowdoesrockbecomebrokendowninthefirstplacetoformthesedimentsthatmakeupsedimentary rocks?Overtimewater,wind,heat,andiceweartherockdowncausingittofallapart.Thisprocessiscalled weatheringanderosion.Theweatheredbitsofrockarecarriedbystreams,rivers,wind,glaciers,orreally anythingelsethatcarriesthebitsofweatheredrockawayfromthelargerock.Themostcommonwaysmall bitsofrockarecarriedawayiswaterintheformofstreamsorrivers.Theweatheredbitsofrockarecarried untiltheycan'tmovethemanymorepilingupintoabigpile.Theseweatheredpilesarecalledsediments. Sedimentsareusuallyclassifiedbysize:Gravelisthebiggestfollowedbysand,mud,andsilt. ClasticSedimentaryRock Clasticsedimentaryrocksaresedimentaryrocksformedoutofbrokendownbitsofrocks.Thereareseveral kindsofclasticsedimentaryrocks;theyarecategorizedbythesizeandsometimestheshapeofthepieces thatmakeuptherock.Themostcommonkindsofclasticsedimentaryrocksarecalledconglomerates, breccias,andsandstone. Conglomeratesaremadefrombitsofroundedgravelthatweredepositedusuallybywater.Overtimethe wetpileofsedimentsbecomessoheavythatthegravelgetscompactedtogether,andmineralsinthewater cementthebitsofgraveltogether.Theonlydifferencebetweenconglomeratesandbrecciasis conglomeratesaremadefromroundedgravelandbrecciasaremadefromangledgravel. Conglomeraterock Brecciasrock Sandstoneissimilartoconglomerateandbreccias.Insteadoflargergravel,smallcrystalsofsandarepiledup bywaterorwind.Overtimethepilesgetheavyenoughthatthesandispressedtogetherandcementedby mineralsfoundingroundwater. Fossilsareoftenfoundinsandstone.Livingthingsare trappedinsidecollapsingsandandeventuallyfossilized untilsomeonefindsthem.Thereisaveryfamousfossil thatwasfoundinChinacalledthe“fightingdinosaurs.” Paleontologiststhinkavelociraptorandprotoceratops werefightingandweretrappedbyacollapsingsanddune. Overtimethesanddunehardenedintosandstone preservingthedinosaursforfuturegenerations. OrganicSedimentaryRock Organicsedimentaryrocksareformedfromthedebrisoflife(bothplantsandanimals).Forexample, limestoneisformedoutofdecayedanimalshells.Animalsusecalciumtoformtheirshells.Aftertheanimal dies,theshellfallsapartandthecalciumcombineswithotherelementsandmineralsandhardensintorock. Fossilsareverycommoninthistypeofrock.Anotherexampleofthistypeofrockiscoquina.Coquinais formedfrompiecesofseashellscementedtogether.Coalisalsoacommonorganicsedimentaryrockfrom deadaquaticplantswhichdiedmillionsofyearsago. ChemicalSedimentaryRock Chemicalsedimentaryrocksareformedwhenwaterevaporatesandleavesbehindmineralsthathardeninto rock.Agreatexampleofthiskindofrockissalt.Sorememberwhenyou'reeatingsalt,you'reeatingarock. It'sarockcalledhalite. Remembertoanswerquestionsinschoology!
