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ASTR-1010 Planetary Astronomy

ASTR-1010 Planetary Astronomy. Day - 19. Announcements. Smartworks Chapter 6: Due Thursday, Nov. 4 Smartworks Chapter 7: Due Thursday, Nov. 11 Exam 3 – Tuesday Nov. 16 – Chapters 6, 7, 8 (?). How Old is the Earth?. Age of the Earth – oldest rocks 4.0 Gyr “Zircons” ~4.4 Gyr

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ASTR-1010 Planetary Astronomy

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  1. ASTR-1010Planetary Astronomy Day - 19

  2. Announcements Smartworks Chapter 6: Due Thursday, Nov. 4 Smartworks Chapter 7: Due Thursday, Nov. 11 Exam 3 – Tuesday Nov. 16 – Chapters 6, 7, 8 (?)

  3. How Old is the Earth? • Age of the Earth – oldest rocks 4.0 Gyr • “Zircons” ~4.4 Gyr • Suggest the crust separated from interior ~4.5 Gyrs • Moon rocks ~4.4 Gyr • Therefore, Moon existed by this time.

  4. Impact Energies and these are the small ones

  5. Formation of the Moon • Moon formed in large collision between Earth + Mars-sized protoplanet. • The collision scattered material into Earth orbit; this collected by accretion to form the Moon. • Composition of Moon is like that of Earth’s crust. • Dark areas on Moon (maria) are ancient lava flows from later large impacts.

  6. A Model of the Earth • We model the Earth’s interior by studying earthquakes. • Sound moves at different speeds through different materials. • P (primary) waves travel through solids and liquids. • S (secondary) waves go through solids only. • Earth’s layers are: crust, mantle, liquid outer core, solid inner core

  7. Geology & Habitatbility • Earth's Interior – Seismic waves (Fig 4.14)‏ • Crust – lowest density, Al, Si, Ca • Mantle – rocky “plastic” • Outer Core – molten • Inner Core – solid, Fe, Ni • Earth's Interior – Differentiation • Melting and sedimentation of heavy material to core • Al26 ==> Mg26 contributed a lot of early heat

  8. The Earth’s Interior

  9. The Earth’s Interior • Layers: • Crust: continents (low density silicates) and basins (basalt: higher iron content). • Mantle. • Core (iron, nickel and other dense materials). • Produced by differentiation in the early Earth: dense materials sink; low-density materials rise.

  10. Geology & Habitatbility • Plate Tectonics • What is it? • What causes it? • Evidence • Continental edge fits • Seafloor spreading • Two types of crust • Seafloor crust – young, high density basalt, thin • Continental crust - old, lower density granite, thick

  11. Earth: Tectonism and Magnetism • Laboratory: mid-Atlantic ridge. • Plates spreading apart, new material rises in the gap. • Solidifying material shows magnetic field at the time. • Direction of the field reverses periodically. • Rock ages reveal rates of continental drift.

  12. Mid-Atlantic Ridge

  13. Tectonism • Interior heat flows to the surface, producing volcanoes and motion of continental plates. • Crustal plates are moved around by convection. • Convection = rising and falling of hot/cold material. • Motion of interior material also generates magnetic fields. Planet rotation may also be important.

  14. Earth’s Magnetic Field

  15. Magnetic Field • Loss of Atmosphere • Thermal escape – light favored over heavy • Impacts • Solar wind stripping • Cause • Electrically conducting interior fluid layer • Convection in the fluid layer • Moderate to fast rotation (dynamo effect)

  16. Magnetosphere & Solar Wind • Magnetosphere • Protects surface and atmosphere from direct impact • Van Allen Belts • Trapped charged particles • Directed down to earth at poles

  17. Magnetic Field • Loss of Atmosphere • Thermal escape – light favored over heavy • Impacts • Solar wind stripping • Cause • Electrically conducting interior fluid layer • Convection in the fluid layer • Moderate to fast rotation (dynamo effect)

  18. Magnetosphere & Solar Wind • Magnetosphere • Protects surface and atmosphere from direct impact • Van Allen Belts • Trapped charged particles • Directed down to earth at poles

  19. Plate tectonics is involved in the formation of the three major categories of rocks: • igneous rocks • cooled from molten material • sedimentary rocks • formed by the action of wind, water, and ice • metamorphic rocks • altered in the solid state by extreme heat and pressure

  20. Plate tectonics, or movement of the plates, is driven by convection within the asthenosphere • Molten material wells up at oceanic rifts, producing seafloor spreading, and is returned to the asthenosphere in subduction zones • As one end of a plate is subducted back into the asthenosphere, it helps to pull the rest of the plate along

  21. Plate tectonics is responsible for most of the major features of the Earth’s surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans

  22. Major Tectonic Plates

  23. Earth’s Changing SurfaceLecture Tutorial pg. 99 • Work with a partner! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you both agree on and write complete thoughts into your LT. • If you get stuck or are not sure of your answer, ask another group. • 8 Minutes

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