7Why have the planets turned out so differently, when they formed at the same time from the same materials?
8Earth as a PlanetOur Goals for Learning • Why is Earth geologically active? • What processes shape Earth’s surface? • How does Earth’s atmosphere affect the planet?
9Why 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?So let’s see what that interior is and why it’s hot.
10Internal Structure, by density Remove lithosphere label & arrow, and dotted circle
11Internal 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.
12The thickness of the lithosphere controls many geological processes Remove lithosphere label & arrow, and dotted circle
14Sources of Internal Heat Gravitational potential energy of accreting planetesimalsDifferentiationRadioactivity
15Why 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.
16Why 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.
17Differentiation Layers ordered by density Highest density on the bottomGravity sorts materials by density.Differentiation converts gravitational potential energy to heat.
18Do 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.
19Do 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.
20Heat Drives Geological Activity Convection: hot rock rises, cool rock falls.1 cycle takes 100 million years on Earth.
21A large planet… Is still warm inside Has a convecting mantle Has a thinner, weaker lithosphereHas molten rock nearer the surfacewhich makes it more geologically active
22Comparing the PlanetsWhich planets have the most and least geological activity?
23Planetary magnetic fields Moving charged particles create magnetic fields.So can a planet’s interior, if the core it electrically conducting, convecting, and rotatingFigure 7.5 goes here.
24Earth’s Magnetosphere Earth’s magnetic fields protects us from charged particles from the SunThe charged particles can create aurorae (“Northern lights”)Figure 7.6ab NEW should go here.
25How 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.
26How 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.Specifically, different kinds of seismic waves propagate at different speeds and directions through the planetary interior depending on the properties of the internal layers.
28Impact CrateringFigure 3e but of course it ain’t on the cd. (huh, and figure 10.7 isn’t either.)This figure is Mars.
29Impact 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
30Volcanism 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)
31Volcanism Erases other geological features Provided gas for our atmosphereProvided water for our oceans
32Why 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.
33Why 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.
34Tectonics and Plate Tectonics Tectonics: any surface reshaping from forces on the lithospherePlate tectonics: pieces of lithosphere moving aroundOnly Earth has plate tectonics.Internal Heat Required!
35ErosionWearing down or building up of geological features by wind, water and ice (weather)Important on Earth - why?
36How does Earth’s atmosphere affect Earth? Erosion (already mentioned)Protection from radiationChanges the surface temperature: greenhouse effectMakes the sky blue!
37Radiation ProtectionAll X-ray light absorbed very high in the atmosphere.Ultraviolet light absorbed by ozone (O3)Figure 7.13a would be good here.
39A 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.
40Mercury and the Moon: Geologically Dead Our Goals for LearningWas there ever geological activity on the Moon or Mercury?
41MoonFigure 7.15, make a line pointing to the Mare Humorum.Some volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria.The Moon is now geologically dead.
42Mercury Plenty of craters - including a huge ‘basin’ Figure 7.17aPlenty of craters - including a huge ‘basin’Smooth plains from volcanism (recent or long ago???)
43Did Mercury shrink?Figure 7.18Steep long cliffs formed when the core cooled, shrinking the planet by ~20 km.Mercury is now geologically dead.
44Mars: A Victim of Planetary Freeze-drying Our Goals for LearningWhat geological features tell us that water once flowed on Mars?Why did Mars change?
45Mars vs. Earth 50% Earth’s radius, 10% Earth’s mass 1.5 A.U from the SunAxis 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 greenhouseSo main difference is … Mars is SMALLER!
46Surface of Mars appears to have ancient river beds
47Eroded craterCondition of craters indicates surface history
58Venus: A Hothouse World Our Goals for LearningIs Venus geologically active?Why is Venus so hot?
59Is Venus geologically active? Figure 7.29 bc and maybe d..Radar images show lots of volcanic & tectonic features, as expected for a large terrestrial planet
60Why is Venus so hot? Greenhouse effect. But why is it so prominent on Venus?Answer: Thick CO2 atmosphere of Venus locks heat in
61(and some in plant life and in the ocean) Where is Earth’s CO2?Rocks - like limestone(and some in plant life and in the ocean)Why did this happen on Earth and not on Venus?Venus lacks oceans to dissolve the carbon dioxide and lock it away in rock on the seafloorAnd why is that?‘strip tease’ of bullet-by-bullet unveiling is warranted on this slide
62We can understand Venus’ history by thinking about what would happen if Earth were moved to Venus’ orbit.How would the initial heating affect the oceans and the greenhouse effect?
63A runaway greenhouse effect would then occur. Eventually, water molecules would break down & escape to space, just as apparently happened on Venus
64Earth as a Living Planet Our Goals for LearningWhat unique features on Earth are important for human life?How might human activity change our planet?What makes a planet habitable?
65What unique features of Earth are important for life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stability
66What unique features of Earth are important to human life? Earth’s distance from the Sun and moderate greenhouse effect make liquid water possibleSurface liquid waterAtmospheric oxygenPlate tectonicsClimate stability
67What unique features of Earth are important to human life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityPHOTOSYNTHESIS (plant life) is required to make high concentrations of O2, which produces the protective layer of O3.
68What unique features of Earth are important to human life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityPlate tectonics are an important step in the carbon dioxide cycle.
70What unique features of Earth are important to human life? Surface liquid waterAtmospheric oxygenPlate tectonicsClimate stabilityThe CO2 cycle acts like a thermostat for the Earth’s temperature.
71These 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 oxygenFor example:atmospheric oxygen allows life on landStable climate good for lifeWater may enable plate tectonics
72Earth’s ice ages end as oceans freeze over and volcanoes release CO2 into the atmosphere
73Human activity is increasing the concentration of greenhouse gases in the atmosphere, which may strengthen the greenhouse effect and lead to global warming.
74What makes a planet habitable? Located at an optimal distance from the Sun for liquid water to exist.
75What makes a planet habitable? Large enough for geological activity to release & retain water and atmosphere.
76Planetary DestinyEarth is habitable because it is large enough to remain geologically active and at the right distance from the Sun so oceans could form.
77What have we learned?• What unique features of Earth are important for life?Unique features of Earth on which we depend for survival are(1) surface liquid water, made possible by Earth’s moderate temperature;(2) atmospheric oxygen, a product of photosynthetic life;(3) plate tectonics, driven by internal heat; and(4) climate stability, a result of the carbon dioxide cycle, which in turn requires plate tectonics.
78What have we learned? • What makes a planet habitable? We can trace Earth’s habitability to its relatively large size and its distance from the Sun.Its size keeps the internal heat that allowed volcanic outgassing to lead to our oceans and atmosphere, and also drives the plate tectonics that helps to regulate our climate through the carbon dioxide cycle.Its distance from the Sun is neither too close nor too far, thereby allowing liquid water to exist on Earth’s surface.