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Chapter 7 Earth and the Terrestrial Worlds

Chapter 7 Earth and the Terrestrial Worlds. Mercury craters smooth plains, cliffs. Venus volcanoes few craters. Radar view of a twin-peaked volcano. Mars some craters volcanoes riverbeds?. Moon craters smooth plains. Earth volcanoes craters mountains riverbeds.

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Chapter 7 Earth and the Terrestrial Worlds

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  1. Chapter 7Earth and the Terrestrial Worlds

  2. Mercurycraterssmooth plains,cliffs

  3. Venusvolcanoesfew craters Radar view of a twin-peaked volcano

  4. Marssome cratersvolcanoesriverbeds?

  5. Mooncraterssmooth plains

  6. Earthvolcanoescratersmountainsriverbeds

  7. Why have the planets turned out so differently, when they formed at the same time from the same materials?

  8. Our Goals for Learning• Why is Earth geologically active?• What processes shape Earth’s surface?• How does Earth’s atmosphere affect the planet? Earth as a Planet

  9. Why is Earth geologically active? Short answer: the Earth is big enough to still have a hot interior. So what do we know about the interior of the Earth and why is it hot?

  10. Internal Structure, by density

  11. Internal structure, by rock strength The “lithosphere” is the cool rigid rock that forms a planet’s outer layer: the crust and some of the mantle. The lithosphere floats on the lower layers.

  12. The thickness of the lithosphere controls many geological processes

  13. Internal Structure of the Terrestrial Planets

  14. Sources of Internal Heat • Gravitational potential energy of accreting planetesimals • Differentiation • Radioactivity

  15. Why do water and oil separate? • Water molecules repel oil molecules electrically. • Water is denser than oil, so oil floats on water. • Oil is more slippery than water, so it slides to the surface of the water. • Oil molecules are bigger than the spaces between water molecules.

  16. Why do water and oil separate? • Water molecules repel oil molecules electrically. • Water is denser than oil, so oil floats on water. • Oil is more slippery than water, so it slides to the surface of the water. • Oil molecules are bigger than the spaces between water molecules.

  17. Differentiation • Layers ordered by density • Highest density on the bottom • Gravity sorts materials by density. • Differentiation converts gravitational potential energy to heat.

  18. Do rocks s-t-r-e-t-c-h? • No - rock is rigid and cannot deform without breaking. • Yes - but only if it is molten rock. • Yes - rock under strain may slowly deform.

  19. Do rocks s-t-r-e-t-c-h? • No - rock is rigid and cannot deform without breaking. • Yes - but only if it is molten rock. • Yes - rock under strain may slowly deform.

  20. Heat Drives Geological Activity Convection: hot rock rises, cool rock falls. 1 cycle takes 100 million years on Earth.

  21. A large planet… • Is still warm inside • Has a convecting mantle • Has a thinner, weaker lithosphere • Has molten rock nearer the surface which makes it more geologically active

  22. Comparing the Planets Which planets have the most and least geological activity?

  23. Planetary magnetic fields Moving charged particles create magnetic fields. So can a planet’s interior, if the core it electrically conducting, convecting, and rotating

  24. Earth’s Magnetosphere Earth’s magnetic fields protects us from charged particles from the Sun The charged particles can create aurorae (“Northern lights”)

  25. How do we know what is inside the Earth? • We can drill deep inside the Earth. • We can use optical fibers to see deep inside the Earth. • X-ray machines allow us to view the inside of the Earth. • Seismic waves generated by earthquakes probe the Earth’s interior.

  26. How do we know what is inside the Earth? • We can drill deep inside the Earth. • We can use optical fibers to see deep inside the Earth. • X-ray machines allow us to view the inside of the Earth. • Seismic waves generated by earthquakes probe the Earth’s interior.

  27. What processes shape Earth’s surface? • Impact cratering • Volcanism • Tectonics • Erosion

  28. Impact Cratering

  29. Impact Cratering • Moon must be hit as often as Earth. • Where are Earth’s craters? • Erased by volcanic activity and erosion. The more craters, the older the surface

  30. Volcanism Molten rock rises when it is: • Less dense than its surroundings. • Squeezed by its surroundings. • Pushed by expanding trapped gas (water vapor, CO2, N2, H2S, SO2)

  31. Volcanism • Erases other geological features • Provided gas for our atmosphere • Provided water for our oceans

  32. Why doesn’t Mars have as much volcanic activity as Earth? • It’s too far from the Sun, so it cooled off faster. • It’s smaller than the Earth, so it cooled off faster. • It might, we just haven’t seen them erupt yet.

  33. Why doesn’t Mars have as much volcanic activity as Earth? • It’s too far from the Sun, so it cooled off faster. • It’s smaller than the Earth, so it cooled off faster. • It might, we just haven’t seen them erupt yet.

  34. Tectonics and Plate Tectonics Tectonics: any surface reshaping from forces on the lithosphere Plate tectonics: pieces of lithosphere moving around Only Earth has plate tectonics. Internal Heat Required!

  35. Erosion • Wearing down or building up of geological features by wind, water and ice (weather) • Important on Earth - why?

  36. How does Earth’s atmosphere affect Earth? • Erosion (already mentioned) • Protection from radiation • Changes the surface temperature: greenhouse effect • Makes the sky blue!

  37. Radiation Protection • All X-ray light absorbed very high in the atmosphere. • Ultraviolet light absorbed by ozone (O3)

  38. The Greenhouse Effect

  39. A Greenhouse Gas • Any gas that absorbs infrared • Greenhouse gas: molecules with 2 different types of elements (CO2, H2O, CH4) • NOT a greenhouse gas: molecules with single or 2 atoms of the same element (O2, N2) • The Earth is much warmer because of the greenhouse effect than it would be without an atmosphere…but so is Venus. It is only bad if it is a “runaway” effect.

  40. Mercury and the Moon: Geologically Dead • Our Goals for Learning • Was there ever geological activity on the Moon or Mercury?

  41. Moon • Some volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria. • The Moon is now geologically dead.

  42. Mercury • Plenty of craters - including a huge ‘basin’ • Smooth plains from volcanism (recent or long ago???)

  43. Did Mercury shrink? Steep long cliffs formed when the core cooled, shrinking the planet by ~20 km. Mercury is now geologically dead.

  44. Mars: A Victim of Planetary Freeze-drying • Our Goals for Learning • What geological features tell us that water once flowed on Mars? • Why did Mars change?

  45. Mars vs. Earth • 50% Earth’s radius, 10% Earth’s mass • 1.5 A.U from the Sun • Axis tilt about the same as Earth. • Similar rotation period. • Orbit is more elliptical than Earth’s: seasons more extreme in the south than the north. • Thin CO2 atmosphere: little greenhouse • So main difference is … Mars is SMALLER!

  46. Surface of Mars appears to have ancient river beds

  47. Eroded crater Condition of craters indicates surface history

  48. Closeup of eroded crater

  49. Volcanoes…as recent as 180 million years ago…

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