lec24_28nov2011

lec24_28nov2011 - When and how did the cores of terrestrial...

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Ge/Ay133 When and how did the cores of terrestrial planets form?
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Estimated core sizes of the terrestrial planets. Two end member hypotheses for core formation:
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Q: Why is heterogeneous accretion unlikely? Two end member hypotheses for core formation: A: In a gas of solar composition, silicates and iron metal (it IS a reducing environment!) condense over similar ranges in T,P.
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Estimated core sizes of the terrestrial planets. Two end member hypotheses for core formation: For homogeneous accretion, when does the onset of differentiation occur?
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How might we distinguish these, and their timing? Step 1: Know your geochemical affinities!
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Highly siderophile elements in the mantle: Late veneer…
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…or high pressure chemistry? Mixing?
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Step 2: Know how to measure isotopes very well!
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Absolute Pb-Pb dating error bars getting down to ~1 Myr!
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182 Hf 182 W 9
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Once you have ages, can look for short-lived excesses: Hf/W ideal, since Hf is lithophilic, while W is a siderophile & τ 1/2 = 9 Myr.
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Once you have ages, can look for short-lived excesses: Hf/Wdata from meteorites.
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lec24_28nov2011 - When and how did the cores of terrestrial...

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