Astr. 101 Notes 7

Astr. 101 Notes 7 - -Moon-Moon rocks-mare basalt impact...

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-Moon: -Moon rocks-mare basalt, impact breccias, anorthosite; radioactive decay (how we know the ages of various rocks on the Moon) -example: uranium 238 (atomic mass is 238, which is the number of protons plus neutrons; atomic number is 92 protons), lead 206 (atomic number is 82 protons), radioactive decay (of uranium 238 to lead 206; 92 minus 82 is 10 protons; 146 minus 14 is 22 neutrons, leading to 32 nucleotides; if we convert 6 neutrons to protons we get 8 alpha particles; an alpha particle is a helium nucleus; something about beta decay) -half life-how long it takes for an element to lose half of its atoms -zircon crystals-are the oldest rocks on Earth, found in Jack Hills of western Australia, dated to 4.4 Gyr -Moon’s interior-is not symmetrical due to tidal forces of the Earth; the crust is about 60 km thick on the Earth side, and 100 km thick on the far side ; has iron rich core, plastic asthenosphere, solid upper mantle, crust (mare only appears on Earth side, due to thinness of Earth side’s crust) -bombardment-early heavy bombardment cratered entire Moon, late heavy bombardment created giant impact basins that became maria; there has been little bombardment in past 3.8 billion years -tidal recession-Moon’s tidal forces elongate Earth’s oceans along Earth/ Moon line; friction b/w the spinning Earth and its oceans drags the tidal bulge about 10 degrees ahead of alignment w/ the Moon; friction b/w Earth and its oceans also makes the Earth rotate more slowly, increasing the length of the
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