1. 5.3 Atmospheres
Troposphere is where convection takes place – responsible for weather

3. 5.3 Atmospheres
Convection is not possible in the stratosphere, because of the temperature inversions

4. 5.3 Atmospheres
Ionosphere is ionized by high-energy solar radiation, and is good conductor

5. 5.3 Atmospheres
Ionosphere is ionized by high-energy solar radiation, and is good conductor
Reflects radio waves in the AM range, but not FM and TV

6. 5.3 Atmospheres
Ozone layer is between stratosphere and mesosphere; absorbs ultraviolet radiation

7. Discovery 5-1: Earth’s Growing Ozone Hole
Chlorofluorocarbons (CFCs) have been damaging the ozone layer, resulting in ozone hole:

8. 5.3 Atmospheres
Sunlight shines on Earth

9. 5.3 Atmospheres Sunlight shines on Earth
Sunlight that is not reflected is absorbed by Earth’s surface, warming it

10. 5.3 Atmospheres Sunlight shines on Earth
Sunlight that is not reflected is absorbed by Earth’s surface, warming it
Surface re-radiates as infrared thermal radiation

11. 5.3 Atmospheres Sunlight shines on Earth
Sunlight that is not reflected is absorbed by Earth’s surface, warming it
Surface re-radiates as infrared thermal radiation
Atmosphere absorbs some infrared, causing further heating

12. 5.3 Atmospheres Sunlight shines on Earth
Sunlight that is not reflected is absorbed by Earth’s surface, warming it
Surface re-radiates as infrared thermal radiation
Atmosphere absorbs some infrared, causing further heating
This is known as the greenhouse effect

13. End 2/26 lecture

14. Discovery 5-2: The Greenhouse Effect and Global Warming
There is extremely strong evidence that the Earth is getting warmer. The cause of this warming is a subject of intense debate; many scientists believe it is related to the corresponding increase in atmospheric carbon dioxide.

15. Where do atmospheres come from?

16. How are atmospheres lost?

17. The Atmosphere of the Moon
It has essentially NONE!

18. The Atmosphere of the Moon
It has essentially NONE!
WHY?

19. The Atmosphere of the Moon
It has essentially NONE!
WHY?
It has to do with the escape speed

20. Escape Speed and Atmosphere Retention
The "escape speed" is the speed that provides enough energy to achieve an unbound orbit.

21. Escape Speed and Atmosphere Retention
The "escape speed" is the speed that provides enough energy to achieve an unbound orbit.
It is the same for any object -- atom or Atlas rocket

22. Escape Speed and Atmosphere Retention
The "escape speed" is the speed that provides enough energy to achieve an unbound orbit.
It is the same for any object -- atom or Atlas rocket

23. Escape Speed and Atmosphere Retention
For Earth’s surface
11,000 m/s
40,000 km/hr
25,000 mi/hr
For Moon’s surface
2,400 m/s
8,500 km/hr
5,300 mi/hr

24. Escape Speed and Atmosphere Retention
For Earth’s surface
H m/s
N2 515 m/s
O2 480 m/s
For Moon’s surface
H m/s
N2 580 m/s
O2 540 m/s
speed distribution applet

25. Escape Speed and Atmosphere Retention
escape speed = m/s
escape speed = 2400 m/s
For Earth’s surface
H m/s
N2 515 m/s
O2 480 m/s
For Moon’s surface
H m/s
N2 580 m/s
O2 540 m/s

26. The Atmosphere of the Moon
It has essentially NONE!
WHY?
All of it has escaped!

27. 5.4 Interiors

28. 5.4 Interiors Seismic waves:
Earthquakes produce both pressure and shear waves
Pressure waves will travel through both liquids and solids
Shear waves will not travel through liquid, as liquids do not resist shear forces
Wave speed depends on density of material

29. 5.4 Interiors
The pressure wave is a longitudinal wave, while the shear wave is a transverse wave.

30. 5.4 Interiors
The pressure wave is a longitudinal wave, while the shear wave is a transverse wave.
A shear wave cannot propagate within a liquid.

31. 5.4 Interiors
The pressure wave is a longitudinal wave, while the shear wave is a transverse wave.
A shear wave cannot propagate within a liquid.
But a pressure wave can

32. 5.4 Interiors
The speed of P-waves and S-waves depends on the density and state of the matter they pass through.

33. 5.4 Interiors
Can use pattern of P-waves and S-waves during earthquakes to deduce interior structure of Earth:

34. 5.4 Interiors
Currently accepted model:

35. 5.4 Interiors Crust is very thin, rocky, and least dense
Mantle is more dense than crust, but still rocky and much less dense than core
Core is metallic – iron and nickel
Temperature and pressure increase with depth
Outer core is liquid; inner core is solid, due to pressure

36. 5.4 Interiors

37. End 2/28 lecture

38. 5.5 Surface Activity on Earth
Continental drift: Entire Earth’s surface is covered with crustal plates, which can move independently

39. 5.5 Surface Activity on Earth
Continental drift: Entire Earth’s surface is covered with crustal plates, which can move independently
At plate boundaries, get earthquakes and volcanoes (red dots)

40. 5.5 Surface Activity on Earth
The whole process is driven by convection

42. 5.5 Surface Activity on Earth
Plates moving away from each other create rifts

43. 5.5 Surface Activity on Earth
Plates moving away from each other create rifts
Those moving toward each other slide past each other at subduction zones

44. 5.5 Surface Activity on Earth
Plates moving away from each other create rifts
Those moving toward each other slide past each other at subduction zones, creating trenches, mountain ranges, earthquakes, and volcanoes

45. 5.5 Surface Activity on Earth
And this explains why plate boundaries are hotbeds of earthquakes and volcanic activity

46. 5.5 Surface Activity on Earth
If we follow the continental drift backwards, the continents merge into one, called Pangaea:

47. The Moon

48. 5.6 The Surface of the Moon
Moon has large dark flat areas, due to lava flow, called maria (early observers thought they were oceans):

49. 5.6 The Surface of the Moon
The far side of the Moon shows no major maria

50. 5.6 The Surface of the Moon
The far side of the Moon shows no major maria
This is consistent with the far side’s crust being thicker

51. 5.6 The Surface of the Moon
Crater formation: Meteoroid strikes Moon, ejecting material; explosion ejects more material, leaving crater

52. 5.6 The Surface of the Moon
Craters are typically about 10 times as wide as the meteoroid creating them, and twice as deep.
Rock is pulverized to a much greater depth.
Most lunar craters date to at least 3.9 billion years ago; much less bombardment since then.

53. 5.6 The Surface of the Moon
Very large and very small lunar craters:

54. 5.6 The Surface of the Moon
Regolith: thick layer of dust left by meteorite impacts
Moon is still being bombarded, especially by very small “micrometeoroids”
This softens its surface features

55. The Earth’s Magnetosphere

56. 5.7 Magnetospheres
The magnetosphere is the region around the Earth where charged particles from the solar wind are trapped:

57. 5.7 Magnetospheres
These charged particles are trapped in areas called the Van Allen belts, where they spiral around the magnetic field lines:

58. 5.7 Magnetospheres
Near the poles, the Van Allen belts intersect the atmosphere. The charged particles can escape; when they do, they create glowing light called an aurora:

59. 5.8 History of the Earth-Moon System
Current theory of Moon’s origin: glancing impact of Mars-sized body on the still-liquid Earth caused enough material, mostly from the mantle, to be ejected to form the Moon.
Computer model:

60. 5.8 History of the Earth-Moon System
4 billion years ago, the Moon had many craters but no maria. By 3 billion years ago, the maria had formed. Now, they also are covered with craters.

61. Summary of Chapter 5 Earth’s structure, from inside out:
Core, mantle, crust, hydrosphere, atmosphere, magnetosphere
Tides are caused by gravitational effects of Moon and Sun
Atmosphere is mostly nitrogen and oxygen; thins rapidly with increasing altitude
Greenhouse effect keeps Earth warmer than it would otherwise be

62. Summary of Chapter 5
Interior structure is known from studying seismic waves
Crust is made of plates that move independently
Movement at plate boundaries can cause earthquakes, volcanic activity, mountain ranges, and rifts
New crust formed at rifts shows evidence of magnetic field reversals
Earth’s magnetic field traps charged particles from solar wind

63. 5.5 Surface Activity on Earth
As magnetic material moves away from rift, it is aligned with current magnetic field direction

64. 5.5 Surface Activity on Earth
As magnetic material moves away from rift, it is aligned with current magnetic field direction
As the magnetic field changes direction, the alignment changes as well, and this can be detected

65. Summary of Chapter 5
Interior structure is known from studying seismic waves
Crust is made of plates that move independently
Movement at plate boundaries can cause earthquakes, volcanic activity, mountain ranges, and rifts
New crust formed at rifts shows evidence of magnetic field reversals
Earth’s magnetic field traps charged particles from solar wind

66. Summary of Chapter 5 Main surface features on Moon: maria, highlands
Heavily cratered
No atmosphere and large day–night temperature excursions
Tidal interactions responsible for synchronicity of Moon’s orbit

67. Summary of Chapter 5 Moon’s surface has both rocky and dusty material
Evidence for volcanic activity
Moon apparently formed as a result of a large object colliding with the Earth