Somenumbers

object radius distance mass earth solar

km AU kg mass mass

Sun 700000 - 2x1030 300000 1

Jupiter 70000 5.2 2x1027 300 0.001

Earth 6400 1 6x1024 1 3x10-6

Mercury 2400 0.4 3x1023 0.05 1.5x10-7

Venus 6000 0.7 5x1024 0.8 2.5x10-6

Mars 3400 1.5 6x1023 0.1 3x10-7

Ceres 475 2.8 9x1020 0.0002 5x10-10

Vesta 260 2.4 3x1020 0.0001 1.5x10-10

Moon 1700 - 7x1022 0.01 3x10-8

Pluto 1200 40 1x1022 0.002 7x10-9

SolarRotaMon•  Innebulartheory,youngSunrotatedmuchfasterthannow.

•  FricMonbetweensolarmagneMcfieldandsolarnebularprobablyslowedtherotaMonoverMme.

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HeavyBombardment

•  LeYoverplanetesimalsbombardedotherobjectsinthelatestagesofsolarsystemformaMon.

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OriginofEarth'sWater•  WatermayhavecometoEarthbywayoficyplanetesimals.

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HowdoweexplaintheexistenceofourMoon?

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GiantImpact

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OddRotaMon•  GiantimpactsmightalsoexplainthedifferentrotaMonaxesofsomeplanets.

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WasoursolarsystemdesMnedtobe?•  FormaMonofplanetsinthesolarnebulaseemsinevitable.

•  Butdetailsofindividualplanetscouldhavebeendifferent.

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AsteroidsandComets

•  LeYoversfromtheaccreMonprocess•  Rockyasteroidsinsidefrostline•  Icycometsoutsidefrostline

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Howdowemeasuretheageofarock?

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RadioacMveDecay•  Someisotopesdecayintoothernuclei.

•  Ahalf-lifeistheMmeforhalfthenucleiinasubstancetodecay.

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ThoughtQuesMon

Supposeyoufindarockoriginallymadeofpotassium-40,halfofwhichdecaysintoargon-40every1.25billionyears.Youopentherockandfind15atomsofargon-40foreveryatomofpotassium-40.Howlongagodidtherockform?a)1.25billionyearsagob)2.5billionyearsagoc)3.75billionyearsagod)5billionyearsago

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ThoughtQuesMonSupposeyoufindarockoriginallymadeof

potassium-40,halfofwhichdecaysintoargon-40every1.25billionyears.Youopentherockandfind15atomsofargon-40foreveryatomofpotassium-40.Howlongagodidtherockform?a)1.25billionyearsagob)2.5billionyearsagoc)3.75billionyearsagod)5billionyearsago

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Whathavewelearned?•  Howdowemeasuretheageofarock?– Someisotopesdecaywithawell-knownhalf-life.– ComparingtheproporMonsofthoseisotopeswiththeirdecayproductstellsusageofrock.

•  Howdoweknowtheageofthesolarsystem?– RadiometricdaMngindicatesthatplanetsformed4.5billionyearsago.

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Howdoweknowtheageofthesolarsystem?

•  RadiometricdaMngtellsusthatoldestmoonrocksare4.4billionyearsold.

•  Oldestmeteoritesare4.55billionyearsold.•  Planetsprobablyformed4.5billionyearsago.

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ImpactCratersonEarth

• Cratersareveryquickly(ingeologicalterms)erodedawaybywaterandwind.• RelaMvelyfewcratersareevidenttodayonEarth• MassexMncMonsevidentinthefossilrecord–somedefinitelycausedbylargeimpactofasteroid

KnownimpactcratersonEarth:168confirmedcraters

BarringerCrater,Arizona

1kmacross;50,000yearsold;45mmeteoriteofironandnickel

AmguidCrater,Algeria0.45km,age<100,000years

Landsatpicture

Fromtheground

AoroungaCrater,Chad12.6kmAge<365millionyears

Bigachcrater,Kazakhstan8kmAge=5millionyears

BrentCrater,OntarioCanada3.8km396millionyearsold

MoraskoCraterPoland0.1km<10,000yearsold

WolfeCreekWesternAustrailia0.875km<300,000yearsold

TheChicxulubCrater:Yucatan,Mexicoage=65millionyears:theimpactthatcaused

dinosaurstobecomeexMnct

Gravitymap,madebyaPetroleumcompanyWhiteline:coastlineWhitedots:cenotesorsinkholes,aYerMayanworddzonot

ThenoMonthatagiantimpactkilledthedinosaurscamefromthediscovery,byAlvarez,in1980,thatthesedimentsattheK-TboundarywereenrichedinthemetalIridium.EarthrocksarelowinIridium(it’s“allatthecenter”).Itwaswell-knownthatasteroidalmaterial(ironmeteoritesespecially)areenrichedinIridium,Nickel,PlaMnum-groupmetals.Paleontologistsdidn’tlikethisatall(astronomersinfringingontheirfield)butitturnsouttoberight,especiallyifwecanfindthecrater.GeologistslookingforoilidenMfiedapossiblefeatureburiedundersedimentsintheYucatan.ItwasidenMfiedasanimpactcraterbyshockedminerals,gravityanomaly,andtekMtes.OtherevidencefortheageincludesimpactmaterialallaroundtheworldattheK-Tsedimentboundary,increasinginthicknessasoneapproachesthecrater.

CanasteroidalimpactsexplainALLmassexMncMons?Probablynot,butthereareoneortwoothersthatmaybeassociatedwithanimpact.Volcanos,changingoceancurrents,conMnentaldriY,oceanacidificaMon,amongothers,canalsodothetrick.Sothisobjectwasabout20-30milesacross,andleYacraterupwardsof300kminsize.Inclasswe’llmenMonsomeothereffectsofthecollision.HereIwanttoshowyouaTINYcollision,somethingthesizeofanSUV,InRussiainFeb2013.Linktohrps://www.youtube.com/watch?v=ztrU90Ub4UwThisisoneIpickedatrandom,it’sprobablynotthebest.Youcanjustgoogle“2013RussianMeteorburst”orsomethinglikethat.Americanspysatellites,recentlydeclassified,haveshownusmanysuchairbursts,mostlyovertheocean,somewithlirleopMcallight.

TheatmosphereoftheEarth

CurrentdayComposiMon:78%N2,21%O2,1%ArgonTrace:CO2(CarbonDioxide)H2O(Water)O3(ozone)c.f.VenusandMars:95%CO2

GlobalWarmingGreenhousegases:CO2,methane(fromburningcoal,naturalgas,andoil;livestock),nitrousoxide,hydrofluorocarbons

MostimportantGreenhouseGasisCO2

CO2historicrecord•  WecanmeasuretheCO2contentoftheatmosphereasafuncMonofMme,usingbubblestrappedinicelayersinAntarcMca

•  OververylongMmescales,theCO2levelgoesupanddownwiththeiceages:respondstobiosphere,weatheringofrocks,andothergeochemicalprocesses

•  WiththeindustrialrevoluMon,theproducMonofCO2becauseoftheburningoffossilfuelshascausedalargeincreaseintheCO2levels,henceincreasedgreenhouseeffect,orglobalwarming

WhyaretheatmospheresofMarsandVenusandEarthdifferent?Let’sstartwithatmospheres.Youaddthingsbyoutgassing(mostlyvolcanos),andthat’smostlyCO2andH2O.Soall3planetsshouldhavesuchanatmosphere.Soifthisisright,youneedtohideatmosphereormakesomeofitgoaway.Earth:Earthhas170,000xasmuchCO2boundupinlimestoneandshells,anddissolvedinseawater,asithasinitsatmosphere.IfwecouldreleaseallthisCO2we’dbelikeVenus,athickatmosphere,andahugegreenhouseeffect.Inotherwords,theEarth’satmosphereishighlymodified,butthethingsthatcouldbeintheatmospherehavenotdisappeared.Wecouldgetthembackundertherightcircumstances.Example:heatupEarthsomehowàlessCO2inoceanwateràmoreinatmosphere-->atmosphereholdsinmoreheat,etc.Nowtherearefeedbackloopsthatkeepthisfromhappeningingeneral,butwhatifwehelptheEarthgetoutofequilibrium?SomostofEarth’satmosphereisHIDDEN(storedaway).

Mars:wecansee/countMarManvolcanos.They’rehuge.WecancalculatehowmuchCO2andwaterthereshouldbe.Itshouldhaveanatmosphere400xasdenseasitistoday,andthereshouldbelotsofwater.Thatthickatmosphereshouldmakethingswarmer,sothereoughttobelakes,etc,evenoceans.Wheredidtheatmospherego?1)ASMALLamountisfrozenoutinthepolarcaps.2)Someisboundtorocks3)Somewatermightbeunderground(there’sevidenceforthis)4)MostofitwasdestroyedbysolarwindparMclesandbyUVlight.Marscooledoff(inside)fast.Nomoreliquidrocksmovingaround,nomoremagneMcfield,nomoreprotecMonfromsolarwind.NOmoreaddiMonofatmospherebyvolcanos.MarshasnoozonelayertoprotectitfromUVlight.SomostofMars’satmosphereisGONE,someofitishidden.

Venus—VenussMllhasthickCO2atmosphere.Butithasnowater.Venuscan’thaveoceansbecauseit’ssohot.Sothewaterwasagasinatmosphere.AndthewaterwasbrokentoconsMtuentpartsbysolarwindandbyUVlight.Slowlythewaterdisappeared.SoVenus’satmospherekeptthevolcanicsecondaryatmosphere,butlostthewaterinatmosphere.Thesameprocessescreatedtheatmospheres,andsimpleprocessesdestroyedparts(all)oftheatmosphere.TheeffecMvenessdependedonthesizeoftheplanet(howfasttheinteriorcooled),andonthedistancefromtheSun.AndifwecreatedthecondiMonsforarunawaygreenhouseeffectonEarth,thenit’spossibletoturnEarth’satmosphereintosomethingresemblingVenus’s.Conversely,itMIGHTbepossibletoconvertVenus’satmospheretoalow-CO2one.Thetechnologicalandbiologicalchallengesarelarge,andit’saphilosophicalquesMonwhetherweshouldtryevenifwehavethetools.

Aswe’vesaid,wecanunderstandwhytheEarthdoesn’thavealotofimpactcratersfromthefactthatthere’savarietyoferosiveprocesses(erosion).Assumingthattheterrestrialplanetsareprerymuchalikeandsufferedsimilarearlybombardmentisprobablynotbad,aslongaswecanidenMfywaysthatthey’dturnouttobedifferentoverMme.Whatgeologicalprocessescanwethinkof?ImpactsfromouterspaceVolcanosTectonicsErosion:wind,water,ice…Whatmighthelptocontroltheseprocesses?Size(mass),distancefromSun,evoluMonofsurfacecomposiMon…

First,anyobjectthat’sroundhasundergonedifferenMaMon,wheretheheavystuffsinkstomiddleandthelightstufffloatsonsurface.Soweclaimthattheplanetsgothotenoughtodothis.How?EnergyofformaMonRadioacMvity

WhatshapedthesurfaceoftheMoon?EarlybombardmentLavaWhydiditstop?

Whydiditstop?

Moonis“geologically”dead,BUTitsMllhasmoon-quakes.Here’sanastronautdeployingaseismometer.

Thereareatleastfourdifferentkindsofmoonquakes:(1)deepmoonquakesabout700kmbelowthesurface,probablycausedbyMdes;(2)vibraMonsfromtheimpactofmeteorites;(3)thermalquakescausedbytheexpansionofthefrigidcrustwhenfirstilluminatedbythemorningsunaYertwoweeksofdeep-freezelunarnight;and(4)shallowmoonquakesonly20or30kilometersbelowthesurface,[causedbyslumpingofcraterwalls].

There’salsoanearside-farsidedifference.Thenearsidehas“seas”,Thefarsidehardlydoes.Nearsidehasameasurablythinnercrust-butwedon’tknowwhy.NearsidehasmoreradioacMverocks-wedon’tknowwhy.

MercuryisqualitaMvelyliketheMoon.Butithasnohugeseas(lava-filledcraters).Butthecraterdensityisn’tashighasoldestpartsofMoon,implyingthatlavafilledinsomeofthecraters.Mercuryalsohashugebasins-impactcraters.Andcliffs…

Mars-MarsisbiggerthanMercuryorMoonsopresumablyitstayedhotlongerininterior.Therearenorthern/southernhemispheredifferences.Southernhighlandsshowlotsofcraters.Volcanosarethebigdealhere.OlympusMonsisthesizeoftheenMrestateofArizona!Someevidenceforlavaasyoungas200millionyears.Evidencefortectonics.

Clearevidenceforrunningandstandingwaterinthepast,butwatercan’texistforlongonthesurfacetoday-MarsRovershavehelpedalot,doingchemistry/minerologyofrocks.

Venus-thickatmosphere-butwecanuseradartomapthesurface-wehadaradarmapperinorbit.AcMvesurface-lackofcratering.Lotsofevidenceforvolcanos.Notmuchtectonics…Notmucherosion-whynot?

Earth-let’stalkabouttectonicsMoMonsofhugechucksoftherockyoutersurface.First,isitreal?1912-conMnentssortoffittogether.1950s-discoveryofmidoceanridgesandfossilevidence.Now-wecanmeasureusinglasersandGPS

(1)Internally,Earthisdifferen'ated:segregatedintolayers,accordingtodensity

Seismology:bystudyinghowseismicwavestravel,wecanstudytheinternalstructureoftheEarth

P-waves(PressureWaves)andS-waves(Shearortransversewaves)

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Differentiation

•  Gravity pulls high-density material to center.

•  Lower-density material rises to surface.

•  Material ends up separated by density.

InternalstructureoftheEarth

TheEarthisdifferenMatedbecausetheheaviestelementsserledtothecenterwhenitwasyoungandmolten.

Innercore:SOLIDNickelandIronOutercore:LiquidNickelandIronMantle:Semi-solid(plasMc)rockCrust:Granitesandbasalts.

Undertheoceans,thecrustisdensebasaltandisabout7kmthick.UndertheconMnents,thecrustislowerdensitygraniteandisabout30kmthick.

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Lithosphere

•  A planet’s outer layer of cool, rigid rock is called the lithosphere.

•  It “floats” on the warmer, softer rock that lies beneath.

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Heating of Planetary Interiors

•  Accretion and differentiation when planets were young

•  Radioactive decay is most important heat source today.

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Cooling of Planetary Interiors

•  Convection transports heat as hot material rises and cool material falls.

•  Conduction transfers heat from hot material to cool material.

•  Radiation sends energy into space.

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Surface Area–to–Volume Ratio •  Heat content depends on volume. •  Loss of heat through radiation depends on surface

area. •  Time to cool depends on surface area divided by

volume:

•  Larger objects have a smaller ratio and cool more slowly.

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Sources of Magnetic Fields

•  Motions of charged particles are what create magnetic fields.

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Sources of Magnetic Fields

•  A world can have a magnetic field if charged particles are moving inside.

•  Three requirements: –  Molten interior –  Convection –  Moderately rapid

rotation

2.TheEarthisgeologicallyacMve

• Inthepresentday,radioac'vedecayofheavyelementsproducesheatandkeepstheinternalEarthwarmandthegeologyacMve:RadioacMvedecayofPotassium(K),Uranium(U)andThorium(Th)

• Themoltenlayersinthemantleareconstantlybubbling(convec'on)

• Thecrust,orlithosphere,isbrokenintotectonicplateswhichmovearoundontheliquidlayerbelowthem

7MajorTectonicPlates

CurrentplatemoMon,measuredbyGPS

ConvecMoninMantledrivingmoMonoftectonicplates

MoMonsatplateboundaries

Plateboundariesàvolcanos,earthquakes,deepoceantrenches,

conMnentalmountainranges

ConMnentalDriY:Pangea

FormaMonofHawaiianislands:platemoMonoverhotspot

HotSpots

•  TheHawaiianislandshaveformedwhereaplateismovingoveravolcanichotspot.

SurfaceFeatures

•  TheHimalayasformedfromacollisionbetweenplates.

RiYValleyinEastAfrica

SurfaceFeatures

•  TheRedSeaisformedwhereplatesarepullingapart.

SinaiPenninsula&TheRedSea