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Chapter 7 Earth and the Terrestrial Worlds Slide 2 Mercury craters smooth plains, cliffs Slide 3 Venus volcanoes few craters Radar view of a twin- peaked volcano Slide 4 Mars some craters volcanoes riverbeds? Slide 5 Moon craters smooth plains Slide 6 Earth volcanoes craters mountains riverbeds Slide 7 Why have the planets turned out so differently, when they formed at the same time from the same materials? Slide 8 Our Goals for Learning Why is Earth geologically active? What processes shape Earths surface? How does Earths atmosphere affect the planet? Earth as a Planet Slide 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? Slide 10 Internal Structure, by density Slide 11 Internal structure, by rock strength The lithosphere is the cool rigid rock that forms a planets outer layer: the crust and some of the mantle. The lithosphere floats on the lower layers. Slide 12 The thickness of the lithosphere controls many geological processes Slide 13 Internal Structure of the Terrestrial Planets Slide 14 Sources of Internal Heat 1)Gravitational potential energy of accreting planetesimals 2)Differentiation 3)Radioactivity Slide 15 Why do water and oil separate? A.Water molecules repel oil molecules electrically. B.Water is denser than oil, so oil floats on water. C.Oil is more slippery than water, so it slides to the surface of the water. D.Oil molecules are bigger than the spaces between water molecules. Slide 16 Why do water and oil separate? A.Water molecules repel oil molecules electrically. B.Water is denser than oil, so oil floats on water. C.Oil is more slippery than water, so it slides to the surface of the water. D.Oil molecules are bigger than the spaces between water molecules. Slide 17 Differentiation Layers ordered by density Highest density on the bottom Gravity sorts materials by density. Differentiation converts gravitational potential energy to heat. Slide 18 Do rocks s-t-r-e-t-c-h? A.No - rock is rigid and cannot deform without breaking. B.Yes - but only if it is molten rock. C.Yes - rock under strain may slowly deform. Slide 19 Do rocks s-t-r-e-t-c-h? A.No - rock is rigid and cannot deform without breaking. B.Yes - but only if it is molten rock. C.Yes - rock under strain may slowly deform. Slide 20 Heat Drives Geological Activity Convection: hot rock rises, cool rock falls. 1 cycle takes 100 million years on Earth. Slide 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 Slide 22 Comparing the Planets Which planets have the most and least geological activity? Slide 23 Planetary magnetic fields Moving charged particles create magnetic fields. So can a planets interior, if the core it electrically conducting, convecting, and rotating Slide 24 Earths Magnetosphere Earths magnetic fields protects us from charged particles from the Sun The charged particles can create aurorae (Northern lights) Slide 25 How do we know what is inside the Earth? A.We can drill deep inside the Earth. B.We can use optical fibers to see deep inside the Earth. C.X-ray machines allow us to view the inside of the Earth. D.Seismic waves generated by earthquakes probe the Earths interior. Slide 26 How do we know what is inside the Earth? A.We can drill deep inside the Earth. B.We can use optical fibers to see deep inside the Earth. C.X-ray machines allow us to view the inside of the Earth. D.Seismic waves generated by earthquakes probe the Earths interior. Slide 27 What processes shape Earths surface? 1)Impact cratering 2)Volcanism 3)Tectonics 4)Erosion Slide 28 Impact Cratering Slide 29 Moon must be hit as often as Earth. Where are Earths craters? Erased by volcanic activity and erosion. The more craters, the older the surface Slide 30 Volcanism Molten rock rises when it is: Less dense than its surroundings. Squeezed by its surroundings. Pushed by expanding trapped gas (water vapor, CO 2, N 2, H 2 S, SO 2 ) Slide 31 Volcanism Erases other geological features Provided gas for our atmosphere Provided water for our oceans Slide 32 Why doesnt Mars have as much volcanic activity as Earth? A.Its too far from the Sun, so it cooled off faster. B.Its smaller than the Earth, so it cooled off faster. C.It might, we just havent seen them erupt yet. Slide 33 Why doesnt Mars have as much volcanic activity as Earth? A.Its too far from the Sun, so it cooled off faster. B.Its smaller than the Earth, so it cooled off faster. C.It might, we just havent seen them erupt yet. Slide 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! Slide 35 Erosion Wearing down or building up of geological features by wind, water and ice (weather) Important on Earth - why? Slide 36 How does Earths atmosphere affect Earth? 1)Erosion (already mentioned) 2)Protection from radiation 3)Changes the surface temperature: greenhouse effect 4)Makes the sky blue! Slide 37 Radiation Protection All X-ray light absorbed very high in the atmosphere. Ultraviolet light absorbed by ozone (O 3 ) Slide 38 The Greenhouse Effect Slide 39 A Greenhouse Gas Any gas that absorbs infrared Greenhouse gas: molecules with 2 different types of elements (CO 2, H 2 O, CH 4 ) NOT a greenhouse gas: molecules with single or 2 atoms of the same element (O 2, N 2 ) The Earth is much warmer because of the greenhouse effect than it would be without an atmospherebut so is Venus. It is only bad if it is a runaway effect. Slide 40 Mercury and the Moon: Geologically Dead Our Goals for Learning Was there ever geological activity on the Moon or Mercury? Slide 41 Moon Some volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria. The Moon is now geologically dead. Slide 42 Mercury Plenty of craters - including a huge basin Smooth plains from volcanism (recent or long ago???) Slide 43 Did Mercury shrink? Steep long cliffs formed when the core cooled, shrinking the planet by ~20 km. Mercury is now geologically dead. Slide 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? Slide 45 Mars vs. Earth 50% Earths radius, 10% Earths mass 1.5 A.U from the Sun Axis tilt about the same as Earth. Similar rotation period. Orbit is more elliptical than Earths: seasons more extreme in the south than the north. Thin CO 2 atmosphere: little greenhouse So main difference is Mars is SMALLER! Slide 46 Surface of Mars appears to have ancient river beds Slide 47 Condition of craters indicates surface history Eroded crater Slide 48 Closeup of eroded crater Slide 49 Slide 50 Volcanoesas recent as 180 million years ago Slide 51 Past tectonic activity Slide 52 Low-lying regions may once have had oceans Slide 53 Slide 54 Opportunity Spirit Slide 55 2004 Opportunity Rover provided strong evidence for abundant liquid water on Mars in the distant past. How could Mars have been warmer and wetter in the past? Slide 56 Today, most water lies frozen underground (blue regions) Some scientists believe accumulated snowpack melts to carve gullies even today Slide 57 Why did Mars change? Slide 58 Venus: A Hothouse World Our Goals for Learning Is Venus geologically active? Why is Venus so hot? Slide 59 Is Venus geologically active? Radar images show lots of volcanic & tectonic features, as expected for a large terrestrial planet Slide 60 Answer: Thick CO 2 atmosphere of Venus locks heat in Why is Venus so hot? Greenhouse effect. But why is it so prominent on Venus? Slide 61 Where is Earths CO 2 ? 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 seafloor And why is that? Slide 62 We 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? Slide 63 A runaway greenhouse effect would then occur. Eventually, water molecules would break down & escape to space, just as apparently happened on Venus Slide 64 Earth as a Living Planet Our Goals for Learning What unique features on Earth are important for human life? How might human activity change our planet? What makes a planet habitable? Slide 65 What unique features of Earth are important for life? 1)Surface liquid water 2)Atmospheric oxygen 3)Plate tectonics 4)Climate stability Slide 66 What unique features of Earth are important to human life? 1)Surface liquid water 2)Atmospheric oxygen 3)Plate tectonics 4)Climate stability Earths distance from the Sun and moderate greenhouse effect make liquid water possible Slide 67 What unique features of Earth are important to human life? 1)Surface liquid water 2)Atmospheric oxygen 3)Plate tectonics 4)Climate stability PHOTOSYNTHESIS (plant life) is required to make high concentrations of O 2, which produces the protective layer of O 3. Slide 68 What unique features of Earth are important to human life? 1)Surface liquid water 2)Atmospheric oxygen 3)Plate tectonics 4)Climate stability Plate tectonics are an important step in the carbon dioxide cycle. Slide 69 The Carbon Dioxide Cycle Slide 70 What unique features of Earth are important to human life? 1)Surface liquid water 2)Atmospheric oxygen 3)Plate tectonics 4)Climate stability The CO 2 cycle acts like a thermostat for the Earths temperature. Slide 71 These 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 Slide 72 Earths ice ages end as oceans freeze over and volcanoes release CO 2 into the atmosphere Slide 73 Human activity is increasing the concentration of greenhouse gases in the atmosphere, which may strengthen the greenhouse effect and lead to global warming. Slide 74 What makes a planet habitable? Located at an optimal distance from the Sun for liquid water to exist. Slide 75 What makes a planet habitable? Large enough for geological activity to release & retain water and atmosphere. Slide 76 Planetary Destiny Earth is habitable because it is large enough to remain geologically active and at the right distance from the Sun so oceans could form. Slide 77 What 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 Earths 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. Slide 78 What have we learned? What makes a planet habitable? We can trace Earths 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 Earths surface.