Lecture_8_Timing2

Lecture_8_Timing2 - B u ild in g a H a b ita b le P la n e...

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1 1 Building a Habitable Planet: Timing • Universe (Hubble relationship) • Elements (today) • Solar System - Earth (last lecture) • Differentiation (Core, Mantle, Atmosphere) • Further Differentiation (Crust/Mantle) Radioactivity 2
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2 3 Use ratios to solve D 0 problem! 4 III. Another complicated clock for dating the duration of time elements were forming in our galaxy • Our galaxy formed from an initial cloud of H and He • Many large stars have formed over time and ended in supernovae, contributing elements to the interstellar cloud from which our sun formed • Long lived radionuclides ( 235 U, 238 U, 232 Th ) are produced in fixed ratios in supernovae
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3 5 III. Another complicated clock for dating the duration of time elements were forming in our galaxy 235 U 238 U 232 Th Half life (billions of years) 0.75 4.47 14 Relative production in supernovae 0.79 0.525 1.00 After a very long time of constant production 0.041 0.167 1.00 Assume supernovae are gradually contribute elements to the interstellar cloud As radionuclides from older explosions decay, the shorter lived radionuclides become less abundant relative to the longer lived radionuclides 6 96.9 96.9 193.8 5 93.8 93.8 187.5 4 87.5 87.5 175 3 75 75 150 2 50 50 100 1 Bal WD Bal Week Rules: •Rate (how much/time) of addition is constant •Rate of withdrawal depends on how much is there Result: •Asymptotic approach to steady state value Steady state: the state of the system (bank account) no longer changes, but there is still flow in and out
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Lecture_8_Timing2 - B u ild in g a H a b ita b le P la n e...

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