Chapter9:HISTORYOFEARTH

TheEssentialEarth,2ndEdition

ThomasH.Jordan&JohnGrotzinger

©2012byW.H.FreemanandCompany

HistoryofEarth• Earthis4.56BillionYearsOld

• Earthhasexperiencedarichanddiversehistorythatwewillexploreinthischapter

FormationoftheSolarSystem

• NebularHypothesis• Matterwithinagivenorbit

accretestogethertoeventuallyformplanets

• Leadstoformationofplanetsthatrotatewithinorbitsaroundthesun

TheSolarSystem

• Innerrockyplanetsformedfromtheaccretionofdensematerials

• Outergaseousplanetsformedfromtheaccretionoflessdensematerials

• Note:Plutoisnolongeraplanetasof2006

EarlyEarth

• Earthwasveryhotatitsorigin

• Violentimpactsfromplanetesimalsandotherbodieswerecommon

• ElementswithinEarthdifferentiatedtoformlayeredinternalstructure

EarlyEarth:AGiantImpact!

EarlyEarth:Differentiation EarlyEarth:Atmosphere&Oceans

• LightelementsthatmakeupouratmosphereandoceanswereaggregatedtoEarthfromplanetesimals

• Volcanicdegassingfedthemoleculestoearlyatmosphereandoceans

EarlyHistoryofInnerPlanets

• Earthhadlargelydifferentiatedby4.4Billionyearsago

• Otherinnerplanetsexperiencedsimilardifferentiationduringthistime

• Significantdifferencesareevidentintherelativesizesoftheseplanets’cores

• Earth’smoonpreservesahistoryofearlysolarsystemeventssinceitscrusthasnotbeenconstantlyrecycledthroughplatetectonicprocesses

EarlyHistoryofInnerPlanets

• Moon’ssurfaceprovidesarecordofimpactbombardmenthistory

Earth:EvolutionoftheContinents

• ContinentalcrustcontainstheoldestcrustalmaterialonEarth

• Continentsaredividedintotectonicprovinces,whicharelarge‐scaleregionsformedbyaparticularsetoftectonicprocesses.

• NorthAmericaprovidesawell‐knownexampleoftectonicprovinces

NorthAmericanProvinces

CanadianShield• OldestpartoftheNorthAmericancrust

• Precambriangraniticandmetamorphicrocks

InteriorPlatform• Precambrianbasalrocks(sameasonShield)areoverlainbyPaleozoicsedimentaryrocks

• Basinanddomestructures• Basinsaccumulaterelativelythicksedimentarypackages

AppalachianFoldBeltDeformationfrommultiplePaleozoicorogenies

RecordsthehistoryoftheassemblyofPangaea

N.AmericanCordilleraDeformationfromMesozoicandCenozoictectonicactivity

RecordsthehistoryoftheFarallonPlatebeneathNorthAmericancontinent

GlobalTectonicProvinces• Othercontinentshavesimilartectonicprovinces• Continentsarebuiltbyorogenicactivityaroundstablecontinental

nucleicalledcratons• CratonsconsistofPrecambrianshieldandplatformrocks

ContinentalGrowth• Magmaticaddition:Insubductionzones,differentiationofsilica‐richrockproducesnewcontinentalcrustalmaterial– VerticalProcess

• Accretion:Fragmentofbuoyant,continentalcrustbecomesattachedtotheedgeofacratonthroughtectonicprocesses– HorizontalProcess

• Accretedterrainscanbeidentifiedalongcontinentalmargins

ContinentalModificationOrogeniesmodifycontinentsthrough•Metamorphism•Thickeningofcontinentalcrust•Uplift•Productionofstructuralfeaturessuchasthrustfaultsandfold•Meltingoflowercrust

India‐Eurasiacollisionprovidesamodernexampleoforogenicactivity

ContinentalModificationExample:

AssemblyofPangaea

MultipleorogeniesassociatedwiththeassemblyofPangaeamodifiedtheNorthAmericancontinent

TheWilsonCycle:EvolutionofContinents GeologicRecordofWilsonCycle&Supercontinents

BiologicalEventsinEarthHistory

• Theevolutionoflifeisrecordedintherockrecordbyfossils• Lifeinallthreedomainshasoriginatedfromacommon,

universalancestor• Earlyevidenceoflifecomesfrommicrofossilsandchemical

tracesoflife

BiologicalEventsinEarthHistory

MicrobesDominatedinthePrecambrianStromatolitesaresedimentaryfeaturesthatprovideevidenceofabundantmicrobialcommunitiesformuchofEarth’shistory

OxygenationofPrecambrianAtmosphere

• GeologicfeaturesprovideevidenceofthebuildupoffreeoxygeninthePrecambrianoceansandatmosphereasaresultofphotosyntheticactivity

• AsecondstepinoxygenationisobservedattheendofthePrecambrian(600Millionyearsago)

RedBedsBandedIronFormations Grypaniafossils

CambrianExplosion• IntheCambrianperiod,amajorradiationoflifeoccurred

• Allmajorgroupsofanimalsalivetodayoriginatedduringthisradiation

CambrianExplosion

Examplesoffossilsfrombefore(Namacalathus)andafter(HallucigeniaandTrilobites)theCambrianExplosion

HistoryofAnimalDiversityMarkedbyRadiations&Extinctions