M_W_Chapter_19-2_Archean_and_Proterozoic_short_version - What is the Precambrian All rocks below the Cambrian Adam Sedgwick called the basement or

M_W_Chapter_19-2_Archean_and_Proterozoic_short_version -...

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What is the Precambrian?
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Subdivisions of PrecambrianEarly concepts (too simple!!!):Hadean Eon: 4.6 to 4.0 Gano surviving rocks, probably many meteorite impactsArchean Eon: 4.0 to 2.5 Gamostly metamorphic rocks (“basement” of continents)Proterozoic Eon: 2.5 to 0.5 Gaearly sediments, not obviously fossiliferous
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Precambrian Time Scale and TerminologyKeeps being modified! The time-scale in your book (Figure 19.2) is far too detailed for our needs and already out-of-date!
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“Genesis” and the “Hadean”Time before preserved sedimentary record (boundary could change with new discoveries) – 4.6 Ga to about 3.85 GaAccretion and early differentiation (oldest rocks dated are 4.28 Ga)Moon-forming giant impact (4.51 Ga) as boundary between Genesis and Hadean
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“Genesis”Term now being used for first 50 million years of Earth history (4.56-4.51 Ga)Accretion and differentiation4.56 Ga is age of oldest meteorites, considered also to be birth of the Earth from cloud of planetesimals4.51 age of moon – formed by impact between Earth and Mars-sized body (NOT MARS!)
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Growth of planet byaccretion:gravitational energymeteor bombardmentEarth homogenous mixtureof materialsGravitational compression shrinks early EarthGravity concentrated denser materials (Ni & Fe) in centerLess densematerials (silicates) forced to outer layersThe Genesis EarthAccretion
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Compositional ZonesCrustContinentalOceanicMantleCoreOuter (Liquid)Inner (Solid)The Genesis EarthDifferentiation
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PRECAMBRIAN Evolution!AtmosphereCrust-Mantle-CoreDifferentiationTectonicsLife
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“Genesis” and HadeanBombardmentMeteorite impacts and crateringProterozoicArcheanHadeanGenesisFormation of MoonLateheavy bombardment (Earth and Moon)Oldest known rock 4.28 Ga
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What was the Hadean like?
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What was theHadean like?
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Where did our Atmosphere come from?Hadean atmosphereatmosphere of H, HeEarth had no core, no magnetic field, no Van Allen Belts, so solar wind sweeps gases away, atmosphere lost
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  • Fall '08
  • RICHTER
  • Geology, Geological history of Earth, Proterozoic, Archean, nt plate rge

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