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Transcript of Some numbers - University of Arizonaadansonia.as.arizona.edu/~edo/astr170B1_spring2017/...Some...
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.
©2014PearsonEducaMon,Inc.
HeavyBombardment
• LeYoverplanetesimalsbombardedotherobjectsinthelatestagesofsolarsystemformaMon.
©2014PearsonEducaMon,Inc.
OriginofEarth'sWater• WatermayhavecometoEarthbywayoficyplanetesimals.
©2014PearsonEducaMon,Inc.
HowdoweexplaintheexistenceofourMoon?
©2014PearsonEducaMon,Inc.
GiantImpact
©2014PearsonEducaMon,Inc.
OddRotaMon• GiantimpactsmightalsoexplainthedifferentrotaMonaxesofsomeplanets.
©2014PearsonEducaMon,Inc.
WasoursolarsystemdesMnedtobe?• FormaMonofplanetsinthesolarnebulaseemsinevitable.
• Butdetailsofindividualplanetscouldhavebeendifferent.
©2014PearsonEducaMon,Inc.
AsteroidsandComets
• LeYoversfromtheaccreMonprocess• Rockyasteroidsinsidefrostline• Icycometsoutsidefrostline
©2014PearsonEducaMon,Inc.
Howdowemeasuretheageofarock?
©2014PearsonEducaMon,Inc.
RadioacMveDecay• Someisotopesdecayintoothernuclei.
• Ahalf-lifeistheMmeforhalfthenucleiinasubstancetodecay.
©2014PearsonEducaMon,Inc.
ThoughtQuesMon
Supposeyoufindarockoriginallymadeofpotassium-40,halfofwhichdecaysintoargon-40every1.25billionyears.Youopentherockandfind15atomsofargon-40foreveryatomofpotassium-40.Howlongagodidtherockform?a)1.25billionyearsagob)2.5billionyearsagoc)3.75billionyearsagod)5billionyearsago
©2014PearsonEducaMon,Inc.
ThoughtQuesMonSupposeyoufindarockoriginallymadeof
potassium-40,halfofwhichdecaysintoargon-40every1.25billionyears.Youopentherockandfind15atomsofargon-40foreveryatomofpotassium-40.Howlongagodidtherockform?a)1.25billionyearsagob)2.5billionyearsagoc)3.75billionyearsagod)5billionyearsago
©2014PearsonEducaMon,Inc.
Whathavewelearned?• Howdowemeasuretheageofarock?– Someisotopesdecaywithawell-knownhalf-life.– ComparingtheproporMonsofthoseisotopeswiththeirdecayproductstellsusageofrock.
• Howdoweknowtheageofthesolarsystem?– RadiometricdaMngindicatesthatplanetsformed4.5billionyearsago.
©2014PearsonEducaMon,Inc.
Howdoweknowtheageofthesolarsystem?
• RadiometricdaMngtellsusthatoldestmoonrocksare4.4billionyearsold.
• Oldestmeteoritesare4.55billionyearsold.• Planetsprobablyformed4.5billionyearsago.
©2014PearsonEducaMon,Inc.
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)
© 2010 Pearson Education, Inc.
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.
© 2010 Pearson Education, Inc.
Lithosphere
• A planet’s outer layer of cool, rigid rock is called the lithosphere.
• It “floats” on the warmer, softer rock that lies beneath.
© 2010 Pearson Education, Inc.
Heating of Planetary Interiors
• Accretion and differentiation when planets were young
• Radioactive decay is most important heat source today.
© 2010 Pearson Education, Inc.
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.
© 2010 Pearson Education, Inc.
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.
© 2010 Pearson Education, Inc.
Sources of Magnetic Fields
• Motions of charged particles are what create magnetic fields.
© 2010 Pearson Education, Inc.
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