1. Chapter 7 Earth and the Terrestrial Worlds

2. WHAT DO YOU THINK?
Why are Venus (too HOT), Mars (too COLD) and Earth (just right!) so different in their atmospheres?
Could Mars have supported life long ago? How do we know?
Is life known to exist on Mars today?

3. In this chapter you will discover…
Mercury, a Sun-scorched planet with a heavily cratered surface and a substantial iron core
Venus, perpetually shrouded in thick, poisonous clouds and mostly covered by gently rolling hills
Mars, a red, dusty planet that once had running water on its surface and may still have liquid water underground
The role of Carbon Dioxide as a insulator for Planetary climates.

4. Essay Questions
Describe the atmospheres of Venus, Earth, and Mars. Why are these three atmospheres so different?
What does the Martian surface tell us about the planet's history, and future?
Describe the composition of the Moon, and its similarities and differences with our Earth.  How did the Moon form? How do we know?

5. Mercury craters smooth plains cliffs

6. Venus volcanoes few craters
Radar view of a twin-peaked volcano

7. Mars some craters volcanoes riverbeds?

8. Moon craters smooth plains

9. Earth volcanoes craters mountains riverbeds

10. Why have the planets turned out so differently, even though they formed at the same time from the same materials?

11. Earth as a Planet Our goals for learning:
Why is Earth geologically active?
What processes shape Earth’s surface?
How does Earth’s atmosphere affect the planet?

12. Why is Earth geologically active?

13. Earth’s Interior Core: Highest density; nickel and iron
Mantle: Moderate density; silicon, oxygen, etc.
Crust: Lowest density; granite, basalt, etc.

14. Terrestrial Planet Interiors
Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like.

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 Gravity pulls high-density material to center
Lower-density material rises to surface
Material ends up separated by density

18. Thought Question
What is necessary for differentiation to occur in a planet?
It must have metal and rock in it.
It must be a mix of materials of different density.
Material inside must be able to flow.
All of the above.
b and c.

19. Thought Question
What is necessary for differentiation to occur in a planet?
It must have metal and rock in it.
It must be a mix of materials of different density.
Material inside must be able to flow.
All of the above.
b and c.

20. Lithosphere
A planet’s outer layer of cool, rigid rock is called the lithosphere.
It “floats” on the warmer, softer rock that lies beneath.

21. Thought Question 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.

22. Thought Question 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.

23. Strength of Rock
Rock stretches when pulled slowly but breaks when pulled rapidly.
The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.

24. Heat Drives Geological Activity
Convection: hot rock rises, cool rock falls.
One convection cycle takes ~100 million years on Earth.

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

26. Heating of Interior over Time
Accretion and differentiation when planets were young
Radioactive decay is most important heat source today

27. Cooling of Interior
Convection
Conduction
Radiation

28. Cooling of Interior
Convection transports heat as hot material rises and cool material falls
Conduction transfers heat from hot material to cool material
Radiation sends energy into space

29. Thought Question What cools off faster?
A grande-size cup of Starbucks coffee
A teaspoon of cappuccino in the same cup

30. Thought Question What cools off faster?
A grande-size cup of Starbucks coffee
A teaspoon of cappuccino in the same cup

31. Thought Question What cools off faster? A big terrestrial planet
A tiny terrestrial planet

32. Thought Question What cools off faster? A big terrestrial planet
A tiny terrestrial planet

33. Role of Size Smaller worlds cool off faster and harden earlier.
Moon and Mercury are now geologically “dead.”

34. Surface Area to Volume Ratio
Heat content depends on volume.
Loss of heat through radiation depends on surface area.
Time to cool depends on surface area divided by volume:
Larger objects have a smaller ratio and cool more slowly.

35. Planetary Magnetic Fields
Moving charged particles create magnetic fields.
A planet’s interior can create magnetic fields if
- it is electrically conducting, &
- it is circulating and/or rotating.
Figure 7.5 goes here.

36. Earth’s Magnetosphere
Earth’s magnetic fields protects us from charged particles from the Sun.
The charged particles can create aurorae (“Northern lights”).
Figure 7.6ab NEW should go here.

37. Thought Question
If the planet core is cold, do you expect it to have magnetic fields?
Yes, refrigerator magnets are cold, and they have magnetic fields.
No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

38. Thought Question
If the planet core is cold, do you expect it to have magnetic fields?
Yes, refrigerator magnets are cold, and they have magnetic fields.
No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

39. Special Topic: How do we know what’s inside a planet?
P waves push matter back and forth.
S waves shake matter side to side.

40. Special Topic: How do we know what’s inside a planet?
P waves go through Earth’s core, but S waves do not.
We conclude that Earth’s core must have a liquid outer layer.

41. What processes shape Earth’s surface?

42. Geological Processes Impact cratering Volcanism Tectonics Erosion
Impacts by asteroids or comets
Volcanism
Eruption of molten rock onto surface
Tectonics
Disruption of surface by internal stresses
Erosion
Changes made by wind, water, or ice

43. Impact Cratering
Most cratering happened soon after the solar system formed.
Craters are about 10 times wider than objects that made them.
Small craters greatly outnumber large ones.
The Production of a Crater

44. Impact Craters
Meteor Crater (Arizona)
Tycho (Moon)

45. Volcanism
Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface.
Molten rock is called lava after it reaches the surface.

46. Lava and Volcanoes Runny lava makes flat lava plains.
Slightly thicker lava makes broad shield volcanoes.
Thickest lava makes steep stratovolcanoes.

47. Outgassing
Volcanism also releases gases from Earth’s interior into the atmosphere.

48. Tectonics
Convection of the mantle creates stresses in the crust called tectonic forces.
Compression forces make mountain ranges.
A valley can form where the crust is pulled apart.

49. Erosion
Erosion is a blanket term for weather-driven processes that break down or transport rock.
Processes that cause erosion include
Water/Ice movement by glaciers & rivers
Atmospheric Movement by wind, storms
Cyclic heating/cooling

50. Erosion by Water
The Colorado River continues to carve the Grand Canyon.

51. Erosion by Ice
Glaciers carved the Yosemite Valley.

52. Erosion by Wind
Wind wears away rock and builds up sand dunes.

53. Erosional Debris
Erosion can create new features by depositing debris.

54. How does Earth’s atmosphere affect the planet ?

55. Effects of Atmosphere on Earth
Erosion
Makes the sky blue!
Radiation protection
Greenhouse effect

56. Thought Question Why is the sky blue?
The sky reflects light from the oceans.
Oxygen atoms are blue.
Nitrogen atoms are blue.
Air molecules scatter blue light more than red light.
Air molecules absorb red light.

57. Thought Question Why is the sky blue?
The sky reflects light from the oceans.
Oxygen atoms are blue.
Nitrogen atoms are blue.
Air molecules scatter blue light more than red light.
Air molecules absorb red light.

58. Why the sky is blue
Atmosphere scatters blue light from the Sun, making it appear to come from different directions.
Sunsets are red because less of the red light from the Sun is scattered.

59. Earth’s atmosphere absorbs light at most wavelengths.

60. Radiation Protection
All X-ray light is absorbed very high in the atmosphere.
Ultraviolet light is absorbed by ozone (O3) ~ 30 miles high
Figure 7.13a would be good here.

61. The Greenhouse Effect

62. The Greenhouse Effect on Earth
FIGURE 6-4 The Greenhouse Effect
(a) Sunlight and heat from Earth’s interior
warm Earth’s surface, which in
turn radiates energy, mostly as infrared
radiation. Much of this radiation is
absorbed by atmospheric carbon dioxide
and water, heating the air, which
in turn raises Earth’s temperature even
further. In equilibrium, Earth radiates
as much energy as it receives.

63. Greenhouse effect:
Certain molecules let sunlight through but trap escaping infrared photons.
(H2O, CO2, CH4)

64. Greenhouse Gases Any gas that absorbs infrared
Greenhouse gas: often molecules with two different types of elements (CO2, H2O, CH4)
Not a greenhouse gas: molecules with one or two atoms of the same element (O2, N2)

65. Greenhouse Effect: Bad?
The Earth is much warmer because of the greenhouse effect than it would be without an atmosphere…but so is Venus.

66. Earth as a “Living” Planet
What unique features on Earth are important for human life?
How is human activity changing our planet?
What makes a planet habitable?

67. What unique features of Earth are important for life?
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability

68. What unique features of Earth are important to human life?
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Earth’s distance from the Sun and moderate greenhouse effect make liquid water possible.

69. What unique features of Earth are important to human life?
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
PHOTOSYNTHESIS (plant life) is required to make high concentrations of O2, which also produces the protective layer of O3.

70. What unique features of Earth are important to human life?
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Plate tectonics are an important step in the carbon dioxide cycle.

71. Continental Motion
Idea of continental drift was inspired by puzzle-like fit of continents
Mantle material erupts where seafloor spreads

72. Plate Motions

73. Motion of continents can be measured with GPS
Continental Motion
Motion of continents can be measured with GPS

74. Tectonics & Seafloor Recycling
Seafloor is recycled through a process known as subduction

75. Carbon Dioxide Cycle
How does our atmosphere & tectonics combine to regulate temperatures?
How does life play a role?

76. Carbon Dioxide Cycle Step 1: Evaporation/Rain
Liquid water evaporates
Condenses into clouds in lower atmosphere
Rain falls through atmosphere forming Carbonic Acid (H2CO3)
 CO2 gas is absorbed 1

77. Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain
Carbonic Acid (H2CO3) in rivers erodes rocks
Carbonate (CO32-) ion picked up in minerals washed to ocean
Calcium easily absorbed
 CO2 is carried to oceans 2

78. Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life!
Calcium from rocks forms CaCO3 (Calcium Carbonate)
CaCO3 = Limestone
CaCO3 = Coral, Mollusk shells! 3
 CO2 accumulates on seafloor

79. Carbon Dioxide Cycle Step 4: Tectonics & Subduction!
Tectonics gradually pulls seafloor down
CaCO3 broken back into CO2 & other minerals 4
 CO2 now inside crust

80. Carbon Dioxide Cycle Step 5: Volcanic Outgassing!
Eventual Volcanic Activity pushes CO2 back into atmosphere 5
 CO2 now in atmosphere again!

81. Carbon Dioxide Cycle
“Recycle” CO2 from atmosphere to crust to atmosphere over time
Estimate ~25 million years or more for this to occur globally

82. Carbon Dioxide Cycle “Feedback Loop”
Suppose evaporation stopped, during an ice age….
What would happen over time?

83. Carbon Dioxide Cycle Feedback Loop: Ice Age
No evaporation
No Rain
NO CO2 gas absorbed 1

84. Carbon Dioxide Cycle Feedback Loop: Ice Age
No evaporation
No Rain
NO CO2 gas absorbed
But…
Tectonic Activity & Volcanoes continue!
Gradual CO2 concentration increase! 1 5

85. Carbon Dioxide Cycle Feedback Loop: Ice Age
Tectonic Activity & Volcanoes continue!
Gradual CO2 concentration increase!
More Greenhouse Effect => warmer!
Ice Melts!
Cycle restored! 1 5

86. Long-Term Climate Change
Changes in Earth’s axis tilt might lead to ice ages.
Widespread ice tends to lower global temperatures by increasing Earth’s reflectivity.

87. Long-Term Climate Change
CO2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.

88. Carbon Dioxide Cycle “Feedback Loop”
Suppose CO2 in our atmosphere traps too much heat, and we heat up?
What would happen over time?

89. Carbon Dioxide Cycle Feedback Loop: Global Warming
Liquid water evaporates FASTER
MORE Rain
 MORE CO2 gas is absorbed 1 5

90. Carbon Dioxide Cycle Feedback Loop: Global Warming
Volcanoes continue at “normal” rate…
Gradual CO2 concentration decrease!
Less Greenhouse Effect => cooler!
Cycle restored! 1 5

91. What unique features of Earth are important to human life?
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
The CO2 cycle acts like a thermostat for Earth’s temperature.

92. These unique features are intertwined:
Plate tectonics create climate stability
Climate stability allows liquid water
Liquid water is necessary for life
Life is necessary for atmospheric oxygen
For example:
atmospheric oxygen allows life on land
Stable climate good for life
Water may enable plate tectonics
How many other connections between these can you think of?

93. How is human activity changing our planet?

94. Dangers of Human Activity
Human-made CFCs in the atmosphere destroy ozone, reducing protection from UV radiation.
Human activity is driving many other species to extinction.
Human use of fossil fuels produces greenhouse gases that can cause global warming.

95. Global Climate Change
Earth’s average temperature has increased by 0.5°C in the past 50 years.
The concentration of CO2 is rising rapidly.
An unchecked rise in greenhouse gases is leading to global climate change.

96. CO2 Concentration
Global temperatures have tracked CO2 concentration for the last 500,000 years.
Antarctic air bubbles indicate the current CO2 concentration is at its highest level in at least 500,000 years.

97. Most of the CO2 increase has happened in last 50 years!
CO2 Concentration
Most of the CO2 increase has happened in last 50 years!

98. Modeling of Climate Change
Build climate models based on current/past data
Models suggest recent temperature increase is consistent with human production of greenhouse gases.

99. What makes a planet habitable?
Located at an optimal distance from the Sun for liquid water to exist

100. What makes a planet habitable?
Large enough for geological activity to release and retain water and atmosphere

101. Planetary Destiny
Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.

102. Planetary Destiny
Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.