10Earth’s Interior Core: Highest density; nickel and iron Mantle: Moderate density; silicon, oxygen, etc.Crust: Lowest density; granite, basalt, etc.
11Terrestrial Planet Interiors Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like.
12Why 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.
13Why 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.
14Differentiation Gravity pulls high-density material to center. Lower-density material rises to surface.Material ends up separated by density.
15Thought QuestionWhat 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 aboveB and C
16Thought QuestionWhat 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 aboveB and C
17LithosphereA planet’s outer layer of cool, rigid rock is called the lithosphere.It “floats” on the warmer, softer rock that lies beneath.
18Thought 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.
19Thought 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.
20Strength of RockRock 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.
21Heat Drives Geological Activity Convection: Hot rock rises, cool rock falls.One convection cycle takes 100 million years on Earth.
22Sources of Internal Heat Gravitational potential energy of accreting planetesimalsDifferentiationRadioactivity
23Heating of Interior over Time Accretion and differentiation when planets were youngRadioactive decay is most important heat source today.
24Cooling of InteriorConvection transports heat as hot material rises and cool material falls.Conduction transfers heat from hot material to cool material.Radiation sends energy into space.
25Thought Question What cools off faster? A grande-size cup of Starbucks coffeeA teaspoon of cappuccino in the same cup
26Thought Question What cools off faster? A grande-size cup of Starbucks coffeeA teaspoon of cappuccino in the same cup
27Thought Question What cools off faster? A big terrestrial planet A tiny terrestrial planet
28Thought Question What cools off faster? A big terrestrial planet A tiny terrestrial planet
29Role of Size Smaller worlds cool off faster and harden earlier. The Moon and Mercury are now geologically “dead.”
30Surface 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.
31Planetary Magnetic Fields Moving charged particles create magnetic fields.A planet’s interior can create magnetic fields if its core is electrically conducting, convecting, and rotating.
32Earth’s Magnetosphere Earth’s magnetic field protects us from charged particles from the Sun.The charged particles can create aurorae (“Northern lights”).
33Thought QuestionIf 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.
34Thought QuestionIf 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.
35Special Topic: How do we know what’s inside a planet? P waves push matter back and forth.S waves shake matter side to side.
36Special 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.
38Geological Processes Impact cratering Volcanism Tectonics Erosion Impacts by asteroids or cometsVolcanismEruption of molten rock onto surfaceTectonicsDisruption of a planet’s surface by internal stressesErosionSurface changes made by wind, water, or ice
39Impact CrateringMost cratering happened soon after the solar system formed.Craters are about 10 times wider than the objects that made them.Small craters greatly outnumber large ones.
54Earth’s atmosphere absorbs light at most wavelengths.
55Greenhouse effect:Certain molecules let sunlight through but trap escaping infrared photons.(H2O, CO2, CH4)The Greenhouse Effect
56A Greenhouse Gas Any gas that absorbs infrared Greenhouse gas: 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)
57Greenhouse Effect: Bad? Because of the greenhouse effect, Earth is much warmer than it would be without an atmosphere…but so is Venus.
58Thought 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.
59Thought 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.
60Why the sky is blueAtmosphere 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.
61What have we learned? Why is Earth geologically active? Earth retains plenty of internal heat because it is large for a terrestrial planet.That heat drives geological activity, keeping the core molten and driving geological activity.The circulation of molten metal in the core generates Earth’s magnetic field.
62What have we learned? What geological processes shape Earth’s surface? Impact cratering, volcanism, tectonics, and erosionHow does Earth’s atmosphere affect the planet?ErosionProtection from radiationGreenhouse effect
637.2 Mercury and the Moon: Geologically Dead Our goals for learning:Was there ever geological activity on the Moon or Mercury?
64Was there ever geological activity on the Moon or Mercury?
65MoonSome volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria.The Moon is now geologically dead.
66Cratering of MercuryMercury has a mixture of heavily cratered and smooth regions like the Moon.The smooth regions are likely ancient lava flows.
67Cratering of MercuryThe Caloris Basin is the largest impact crater on Mercury.Region opposite the Caloris Basin is jumbled from seismic energy of impact.
68Tectonics on MercuryLong cliffs indicate that Mercury shrank early in its history.
69What have we learned?Was there ever geological activity on the Moon or Mercury?Early cratering on the Moon and Mercury is still present, indicating that activity ceased long ago.Lunar maria resulted from early volcanism.Tectonic features on Mercury indicate early shrinkage.
707.3 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?
71Mars versus Earth 50% Earth’s radius, 10% Earth’s mass 1.5 AU from the SunAxis tilt about the same as EarthSimilar rotation periodThin CO2 atmosphere: little greenhouseMain difference: Mars is SMALLER
72Seasons on MarsSeasons on Mars are more extreme in the southern hemisphere because of its elliptical orbit.
73Storms on MarsSeasonal winds on Mars can drive huge dust storms.
74What geological features tell us that water once flowed on Mars?
75The surface of Mars appears to have ancient riverbeds.
76The condition of craters indicates surface history. Eroded craterThe condition of craters indicates surface history.
84Climate Change on MarsMars has not had widespread surface water for 3 billion years.The greenhouse effect probably kept the surface warmer before that.Somehow Mars lost most of its atmosphere.
85Climate Change on MarsMagnetic field may have preserved early Martian atmosphere.Solar wind may have stripped atmosphere after field decreased because of interior cooling.
86What have we learned?What geological features tell us that water once flowed on Mars?Dry riverbeds, eroded craters, and rock-strewn floodplains all show that water once flowed on Mars.Mars today has ice, underground water ice, and perhaps pockets of underground liquid water.Why did Mars change?Mars’s atmosphere must have once been much thicker for its greenhouse effect to allow liquid water on the surface.Somehow Mars lost most of its atmosphere, perhaps because of a declining magnetic field.
877.4 Venus: A Hothouse World Our goals for learning:Is Venus geologically active?Why is Venus so hot?
91Tectonics on VenusFractured and contorted surface indicates tectonic stresses
92Erosion on VenusPhotos of rocks taken by lander show little erosion
93Does Venus have plate tectonics? Most of Earth’s major geological features can be attributed to plate tectonics, which gradually remakes Earth’s surface.Venus does not appear to have plate tectonics, but its entire surface seems to have been “repaved” 750 million years ago.
95Why is Venus so hot?The greenhouse effect on Venus keeps its surface temperature at 470°C.But why is the greenhouse effect on Venus so much stronger than on Earth?
96Atmosphere of VenusVenus has a very thick carbon dioxide atmosphere with a surface pressure 90 times that of Earth.
97Greenhouse Effect on Venus Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect.Earth escapes this fate because most of its carbon and water are in rocks and oceans.
98Atmosphere of VenusReflective clouds contain droplets of sulfuric acid.The upper atmosphere has fast winds that remain unexplained.
99Runaway Greenhouse Effect More evaporation, stronger greenhouse effectThe runaway greenhouse effect would account for why Venus has so little water.Greater heat, more evaporation
100Thought Question What is the main reason Venus is hotter than Earth? Venus is closer to the Sun than Earth.Venus is more reflective than Earth.Venus is less reflective than Earth.The greenhouse effect is much stronger on Venus than on Earth.Human activity has led to declining temperatures on Earth.
101Thought Question What is the main reason Venus is hotter than Earth? Venus is closer to the Sun than Earth.Venus is more reflective than Earth.Venus is less reflective than Earth.The greenhouse effect is much stronger on Venus than on Earth.Human activity has led to declining temperatures on Earth.
102What have we learned? Is Venus geologically active? Its surface shows evidence of major volcanism and tectonics during the last billion years.There is no evidence for erosion or plate tectonics.Why is Venus so hot?The runaway greenhouse effect made Venus too hot for liquid oceans.All carbon dioxide remains in the atmosphere, leading to a huge greenhouse effect.
1037.5 Earth as a Living Planet Our goals for learning:What unique features of Earth are important for human life?How is human activity changing our planet?What makes a planet habitable?
104What unique features of Earth are important for life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stability
105What unique features of Earth are important for life? Earth’s distance from the Sun and moderate greenhouse effect make liquid water possible.Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stability
106What unique features of Earth are important for life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityPHOTOSYNTHESIS (plant life) is required to make high concentrations of O2, which produces the protective layer of O3.
107What unique features of Earth are important for life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityPlate tectonics is an important step in the carbon dioxide cycle.
108Continental MotionMotion of continents can be measured with GPS.
109Continental MotionIdea of continental drift was inspired by puzzle-like fit of continents.Mantle material erupts where seafloor spreads.
110Seafloor RecyclingSeafloor is recycled through a process known as subduction.
111Plate MotionsMeasurements of plate motions tell us past and future layout of continents.
112Carbon Dioxide Cycle Atmospheric CO2 dissolves in rainwater. Rain erodes minerals that flow into the ocean.Minerals combine with carbon to make rocks on ocean floor.
113Carbon Dioxide CycleSubduction carries carbonate rocks down into the mantle.Rock melts in mantle and outgases CO2 back into atmosphere through volcanoes.
114Long-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.CO2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.
115What unique features of Earth are important for life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityThe CO2 cycle acts like a thermostat for Earth’s temperature.
116These unique features are intertwined: Plate tectonics creates 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?
118Dangers 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.
119Global WarmingEarth’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 will eventually lead to global warming.
120CO2 ConcentrationGlobal 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.
121CO2 ConcentrationMost of the CO2 increase has happened in the last 50 years!
122Modeling of Climate Change Models of global warming that include human production of greenhouse gases are a better match to the global temperature rise.
123What makes a planet habitable? Located at an optimal distance from the Sun for liquid water to exist
124What makes a planet habitable? Large enough for geological activity to release and retain water and atmosphere
125Planetary DestinyEarth 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.
126What have we learned?What unique features of Earth are important for life?Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stability
127What have we learned? How is human activity changing our planet? Human activity is releasing carbon dioxide into Earth’s atmosphere, increasing the greenhouse effect and producing global warming.What makes a planet habitable?Earth’s distance from the Sun allows for liquid water on Earth’s surface.Earth’s size allows it to retain an atmosphere and enough internal heat to drive geological activity.