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GEOLOGY: A Brief Primer Kavli Institute for Theoretical Physics Module 1 This is the first in a series of modules intended for use by teachers of physics and related sciences. They can be used as a tutorial and/or as ancillary materials in the classroom. They have been designed to supplement the various topics in physics. They are based on the 2014 CIDER (Cooperative Institute

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• Slide 1
• Kavli Institute for Theoretical PhysicsModule 1 This is the first in a series of modules intended for use by teachers of physics and related sciences. They can be used as a tutorial and/or as ancillary materials in the classroom. They have been designed to supplement the various topics in physics. They are based on the 2014 CIDER (Cooperative Institute for Deep Earth Research) Conference and developed by the Teachers-In-Residence Program at the KITP.
• Slide 2
• MODULAR 1 GEOLOGY: A BRIEF PRIMER GENERAL OBJECTIVES: 1. To introduce students to the major concepts of geology. 2. To introduce the basic internal structure of the Earth and its associated terminology. 3. To introduce some basic physics-related concepts that govern the dynamics of the internal structures of the Earth, historically to the present day. 4. To introduce the parameters that drive the motions, energy flow, from deep within the planet to the surface, and the consequences that result.
• Slide 3
• Pre-Modular Questions:
• Slide 4
• 1. Most of the Earths mass consists of liquid water. (T/F)
• Slide 5
• Pre-Modular Questions: 1. Most of the Earths mass consists of liquid water. (T/F) 2. The core of the Earth is approximately as large as the Moon. (T/F)
• Slide 6
• Pre-Modular Questions: 1. Most of the Earths mass consists of liquid water. (T/F) 2. The core of the Earth is approximately as large as the Moon. (T/F) 3. The Earth is more dense than the planet Jupiter. (T/F)
• Slide 7
• Pre-Modular Questions: 1. Most of the Earths mass consists of liquid water. (T/F) 2. The core of the Earth is approximately as large as the Moon. (T/F) 3. The Earth is more dense than the planet Jupiter. (T/F) 4. The geometric center of the Earth is so hot, and the pressure is so great that iron there exists as a liquid. (T/F)
• Slide 8
• Pre-Modular Questions: 1. Most of the Earths mass consists of liquid water. (T/F) 2. The core of the Earth is approximately as large as the Moon. (T/F) 3. The Earth is more dense than the planet Jupiter. (T/F) 4. The geometric center of the Earth is so hot, and the pressure is so great that iron there exists as a liquid. (T/F) 5. The deepest interior of the Earth is as hot as the surface of the Sun. (T/F)
• Slide 9
• Question, What does the inside of an avocado have in common with the interior of the Earth?
• Slide 10
• Question, What does the inside of an avocado have in common with the interior of the Earth? Answer: They look very similar!
• Slide 11
• An avocado has an outer skin
• Slide 12
• An avocado has an outer skin The inner flesh
• Slide 13
• An avocado has an outer skin The inner flesh And an inner seed
• Slide 14
• The Earth has:
• Slide 15
• An outer crust
• Slide 16
• The Earth has: An outer crust A mantle
• Slide 17
• The Earth has: An outer crust A mantle And a core
• Slide 18
• The Earth has: An outer crust A mantle And a core *outer
• Slide 19
• The Earth has: An outer crust A mantle And a core *outer *inner
• Slide 20
• The Earth has: An outer crust A mantle And a core *outer *inner An avocado has an outer skin The inner flesh And an inner seed See the similarity???
• Slide 21
• The Earth has: An outer crust A mantle And a core *outer *inner An avocado has an outer skin The inner flesh And an inner seed See the similarity??? Of course, theres much more to it than that!
• Slide 22
• The Earths layers are not static (like an avocado). Besides revolving on its axis, once every 24 hours, and revolving around the sun, every 365 days, the interior of the Earth is a dynamic structure, subtle, but prone to a variety of motions that can cause interesting (and sometimes devastating) effects!
• Slide 23
• The Earths layers are not static (like an avocado). Besides revolving on its axis, once every 24 hours, and revolving around the sun, every 365 days, the interior of the Earth is a dynamic structure, subtle, but prone to a variety of motions that can cause interesting (and sometimes devastating) effects! But first, lets look at some details about these layers.
• Slide 24
• The Earths mass is 5.98 x 10 24 kg. Although it is one of the smallest and least massive of the planets in our solar system, it is one of the most dense planets, with an average density of 5.52 g/cc. (Compare to Jupiter whose density is 1.33 g/cc, or Saturn: 0.687 g/cc)!
• Slide 25
• The Earths mass is 5.98 x 10 24 kg. Although it is one of the smallest and least massive of the planets in our solar system, it is one of the most dense planets, with an average density of 5.52 g/cc. (Compare to Jupiter whose density is 1.33 g/cc, or Saturn: 0.687 g/cc)! However, as you can see, variations in mass means that the density of the different layers can vary, leading to a dynamic system capable of transmitting energy in several ways, having to do with their composition, temperature, and pressure. (These parameters will be treated in other modules.)
• Slide 26
• The depth of each layer is given in the chart below. The Earth is held together by gravitational forces that keep the Earth from breaking apart. However, like going deeper into water, these forces increase with depth, thus increasing the pressure as you go deeper into the Earth.
• Slide 27
• The depth of each layer is given in the chart below. The Earth is held together by gravitational forces that keep the Earth from breaking apart. However, like going deeper into water, these forces increase with depth, thus increasing the pressure as you go deeper into the Earth. Increased pressures means increased temperatures!
• Slide 28
• Here is what the temperature range of the various layers looks like. Temperature and pressure deviations are used to define subdivisions in our basic layers, indicating a transition from one layer to another. The Crust and Rigid part of the Upper Mantle are known as the LITHOSPHERE. The liquid (or flowing) part of the Upper Mantle just below the lithosphere is called the ASTHENOSPHERE. This is then followed by a semi-rigid layer, which defines the inner (LOWER) MANTLE. The Molten Outer Core extends nearly 2000 km beneath that, followed by A SOLID INNER CORE! (Roughly about the size of the Moon!) As hot as the surface of the sun is, the center of the Earth is just as hot!
• Slide 29
• Here is what the temperature range of the various layers looks like. Temperature and pressure deviations are used to define subdivisions in our basic layers, indicating a transition from one layer to another. The Crust and Rigid part of the Upper Mantle are known as the LITHOSPHERE. The liquid (or flowing) part of the Upper Mantle just below the lithosphere is called the ASTHENOSPHERE. This is then followed by a semi-rigid layer, which defines the inner (LOWER) MANTLE. The Molten Outer Core extends nearly 2000 km beneath that, followed by A SOLID INNER CORE! (Roughly about the size of the Moon!) These seemingly alternating layers of liquids, moltens, and solids indicate that the physical and chemical composition of these substances must vary accordingly.
• Slide 30
• Slide 31
• So, how do we know all this?
• Slide 32
• Echo-sounding techniques are used to explore the Earth's crust. Images, similar to sonograms, are produced. A sonogram in the crust is called a seismic reflection. Seismic waves from "small explosions or thumper trucks" return echoes from rock layers. Seismographs pick up these echoes. The Earths crust is the outermost layer of the Earth. It is covered with continental crust and oceanic crust. Rising plumes of heat from the Earth's core cause the plates* to move. The convection currents cause the plates to collide and move apart. Other plates move horizontally past another plate. All plate movement at these boundaries cause both large and small earthquakes. *A plate is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere
• Slide 33
• How do these massive slabs of solid rock float despite their tremendous weight? The answer lies in the composition of the rocks. Continental crust is composed of granitic rocks which are made up of relatively lightweight minerals such as quartz and feldspar. By contrast, oceanic crust is composed of basaltic rocks, which are much denser and heavier. The variations in plate thickness are nature's way of partly compensating for the imbalance in the weight and density of the two types of crust. Because continental rocks are much lighter, the crust under the continents is much thicker (as much as 100 km) whereas the crust under the oceans is generally only about 5 km thick. Like icebergs, only the tips of which are visible above water, continents have deep "roots" to support their elevations. PLATES
• Slide 34
• PLATE TECTONICS The word tectonics comes from a Greek word meaning to build. Tectonic plates are huge moving slabs that together make up Earths outer layer. Some span thousands of miles. In all, a dozen major plates cover Earths surface.
• Slide 35
• Plates migrate atop Earths mantle. Think of the mantle as the top of the flesh of an avocado (but much hotter!!). Temperatures there range from 1,000 to 3,700 Celsius (about 1,800 to 6,700 Fahrenheit). The density of oceanic plates are approximately 3.3 grams per cubic centimeter. Continental crust is only 2.7 grams per cubic centimeter. When these two different types of plates meet the oceanic plate bends and begins to slip underneath the lighter continental plate forming a trench between the plates where they meet. Density is why the continental crust always overrides the heavier oceanic crust. The oceanic crust melts as it forced downward beneath the continental crust. The rocks are recycled and form new igneous rocks when volcanoes erupt.
• Slide 36
• How Plate Tectonics Works: 1. There are two basic types of LITHOSPHERE: continental and oceanic. CONTINENTAL lithosphere has a low density because it is made of relatively light- weight minerals. OCEANIC lithosphere is denser than continental lithosphere because it is composed of heavier minerals. A plate may be made up entirely of oceanic or continental lithosphere, but most are partly oceanic and partly continental.
• Slide 37
• How Plate Tectonics Works: 2. Beneath the lithospheric plates lies the ASTHENOSPHERE, a layer of the mantle composed of denser semi-solid rock. Because the plates are less dense than the asthenosphere beneath them, they are floating on top of the asthenosphere.
• Slide 38
• How Plate Tectonics Works: 3. Deep within the asthenosphere the pressure and temperature are so high that the rock can soften and partly melt. The softened but dense rock can flow very slowly (think of Silly Putty) over geologic time. Where temperature instabilities exist near the core/mantle boundary, slowly moving convection currents may form within the semi-solid asthenosphere.
• Slide 39
• How Plate Tectonics Works: 4. Once formed, convection currents bring hot material from deeper within the mantle up toward the surface.
• Slide 40
• How Plate Tectonics Works: 5. As they rise and approach the surface, convection currents diverge at the base of the lithosphere. The diverging currents exert a weak tension or pull on the solid plate above it. Tension and high heat flow weakens the floating, solid plate, causing it to break apart. The two sides of the now-split plate then move away from each other, forming a DIVERGENT PLATE BOUNDARY.
• Slide 41
• How Plate Tectonics Works: 6. The space between these diverging plates is filled with molten rocks (magma) from below. Contact with seawater cools the magma, which quickly solidifies, forming new oceanic lithosphere. This continuous process, operating over millions of years, builds a chain of submarine volcanoes and rift valleys called a MID-OCEAN RIDGE or an OCEANIC SPREADING RIDGE.
• Slide 42
• How Plate Tectonics Works: 7. As new molten rock continues to be extruded at the mid-ocean ridge and added to the oceanic plate (6), the older (earlier formed) part of the plate moves away from the ridge where it was originally created.
• Slide 43
• How Plate Tectonics Works: 8. As the oceanic plate moves farther and farther away from the active, hot spreading ridge, it gradually cools down. The colder the plate gets, the denser (heavier) it becomes. Eventually, the edge of the plate that is farthest from the spreading ridges cools so much that it becomes denser than the asthenosphere beneath it.
• Slide 44
• How Plate Tectonics Works: 9. As you know, denser materials sink, and thats exactly what happens to the oceanic plateit starts to sink into the asthenosphere! Where one plate sinks beneath another a subduction zone forms.
• Slide 45
• SUBDUCTION: the driving force behind plate tectonics.
• Slide 46
• How Plate Tectonics Works: 10. The sinking lead edge of the oceanic plate actually pulls the rest of the plate behind itevidence suggests this is the main driving force of subduction. Geologists are not sure how deep the oceanic plate sinks before it begins to melt and lose its identity as a rigid slab, but we do know that it remains solid far beyond depths of 100 km beneath the Earths surface.
• Slide 47
• How Plate Tectonics Works: 11. Subduction zones are one type of CONVERGENT PLATE BOUNDARY, the type of plate boundary that forms where two plates are moving toward one another. Notice that although the cool oceanic plate is sinking, the cool but less dense continental plate floats like a cork on top of the denser asthenosphere.
• Slide 48
• How Plate Tectonics Works: 12. When the subducting oceanic plate sinks deep below the Earths surface, the great temperature and pressure at depth cause the fluids to sweat from the sinking plate. The fluids sweated out percolate upward, helping to locally melt the overlying solid mantle above the subducting plate to form pockets of liquid rock (magma).
• Slide 49
• How Plate Tectonics Works: 13. When the subducting oceanic plate sinks deep below the Earths surface, the great temperature and pressure at depth cause the fluids to sweat from the sinking plate. The fluids sweated out percolate upward, helping to locally melt the overlying solid mantle above the subducting plate to form pockets of liquid rock (magma).
• Slide 50
• How Plate Tectonics Works: 14. Some of the molten rock may reach the Earths surface to erupt as the pent- up gas pressure in the magma is suddenly released, forming volcanic (extrusive) rocks. Over time, lava and ash erupted each time magma reaches the surface will accumulatelayer upon layerto construct volcanic mountain ranges and plateaus, such as the Cascade Range and the Columbia River Plateau (Pacific Northwest, U.S.A.).
• Slide 51
• Continental crust Continental crust is much older than oceanic crust. The basement rocks of the continents are granitic rocks. Granitic rocks are lighter than oceanic crust rocks. The minerals that make up the crust are primarily quartz and feldspar. When two crustal plates meet the continental crust is never destroyed. Instead, it overrides oceanic crust or smashes together with another continental crust to form great mountain chains. The Himalaya Mountains are growing as the Eurasian Plate collides with the Indian Plate and the Earths crust is not destroyed.
• Slide 52
• Continental Drift? So over eons, Earths surface has changed a lot. For instance, roughly 250 million years ago, Earth had one giant landmass: Pangaea.
• Slide 53
• Continental Drift? So over eons, Earths surface has changed a lot. For instance, roughly 250 million years ago, Earth had one giant landmass: Pangaea. Within some 50 million years, the plates under that land and the ocean moved. Plate movement split Pangaea into two huge continents, called Laurasia and Gondwanaland.
• Slide 54
• Continental Drift? So over eons, Earths surface has changed a lot. For instance, roughly 250 million years ago, Earth had one giant landmass: Pangaea. Within some 50 million years, the plates under that land and the ocean moved. Plate movement split Pangaea into two huge continents, called Laurasia and Gondwanaland. As Earths plates kept moving, those landmasses each broke apart more. As they spread and traveled, they evolved into our modern continents.
• Slide 55
• Continental Drift? Although some people mistakenly talk about continental drift, its the plates that move. Continents are just the tops of plates that rise above the ocean. We see only the continents atop the plates, just as sailors see only the tips of icebergs at sea. Plates continue to glide slowly across Earths mantle. As the plates move, expect the future placement of continents and oceans to become completely reshuffled. The Atlantic Ocean will open and close over cycles of 300 million to 500 million years.
• Slide 56
• WHAT ABOUT EARTHQUAKES AND VOLCANOES??? 1906 EARTHQUAKE IN SAN FRANCISCO The Indonesian volcano Anak Krakatau erupts at night (credit: Getty Images/Tom Pfeiffer/VolcanoDiscovery)
• Slide 57
• WHAT ABOUT EARTHQUAKES AND VOLCANOES??? 1906 EARTHQUAKE IN SAN FRANCISCO The Indonesian volcano Anak Krakatau erupts at night (credit: Getty Images/Tom Pfeiffer/VolcanoDiscovery) How do Earths GEODYNAMICS account for what happens on the surface???
• Slide 58
• WHAT ABOUT EARTHQUAKES AND VOLCANOES??? There are 20 moving plates under the earths surface, when one of these plates slips past the other; there is a sudden increase in pressure which sometimes breaks the crust. This break in the crust helps releasing the build up pressure in the energy form, which creates huge waves and results in an earthquake. These waves are in the infrasonic range of the human audio spectrum. That is, they are below the audio (hearing) capability of humans.
• Slide 59
• WHAT ABOUT EARTHQUAKES AND VOLCANOES??? While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earths surface, they shake the ground and anything on it, like our houses and us! Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.
• Slide 60
• WHAT ABOUT EARTHQUAKES AND VOLCANOES??? There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water. Earthquakes radiate seismic energy as both body and surface waves.
• Slide 61
• WHAT ABOUT EARTHQUAKES AND VOLCANOES??? The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air. Have you ever heard a big clap of thunder and heard the windows rattle at the same time? The windows rattle because the sound waves were pushing and pulling on the window glass much like P waves push and pull on rock. Sometimes animals can hear the P waves of an earthquake. Dogs, for instance, commonly begin barking hysterically just before an earthquake 'hits' (or more specifically, before the surface waves arrive). Usually people can only feel the bump and rattle of these waves.
• Slide 62
• P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the 'direction of wave propagation'. Lets look at how the P wave moves:
• Slide 63
• Slide 64
• S Waves The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. It is this property of S waves that led seismologists to conclude that the Earth's outer core is a liquid. S waves move rock particles up and down, or side-to-side--perpendicular to the direction that the wave is traveling in (the direction of wave propagation). Lets see how an S wave moves:
• Slide 65
• Slide 66
• Travelling only through the crust, surface waves are of a lower frequency than body waves, and are easily distinguished on a seismogram as a result. Though they arrive after body waves, it is surface waves that are almost entirely responsible for the damage and destruction associated with earthquakes. This damage and the strength of the surface waves are reduced in deeper earthquakes. The first kind of surface wave is called a Love wave, named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves the ground from side-to-side. Confined to the surface of the crust, Love waves produce entirely horizontal motion. Heres how a Love Wave moves:
• Slide 67
• Slide 68
• Rayleigh Waves The other kind of surface wave is the Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves. Heres how a Rayleigh Wave moves:
• Slide 69
• Slide 70
• Slide 71
• Of course, earthquakes CAN be VERY DESTRUCTIVE, depending on where they strike! They are most likely to occur at locations on or near FAULT LINES, where plates meet.
• Slide 72
• But earthquakes can also have other catastrophic effects!!!
• Slide 73
• SUCH AS TSUNAMIS!!
• Slide 74
• Slide 75
• And even VOLCANOES!!
• Slide 76
• How???
• Slide 77
• See how in modular #2 The Dynamics of Physics as demonstrated inside Earth!
• Slide 78
• POST-MODULAR QUESTIONS:
• Slide 79
• 1.The surface, or crust, of the Earth extends this far down: a. 70 km. b. 200 km. c. 500 km. d. 1000 km.
• Slide 80
• POST-MODULAR QUESTIONS: 2.The major interior layer between the Earths crust and core is called the a. semi-rigid Layer. b. O Zone. c. mantle. d. temperate zone.
• Slide 81
• POST-MODULAR QUESTIONS: 3.The primary composition of the Continental Crust is ________ as compared to the Oceanic Crust. a. made up of relatively light weight minerals b. made up of extremely dense minerals c. the same d. molten
• Slide 82
• POST-MODULAR QUESTIONS: 4.Plates is a term used to describe a. the continents of the Earth as we know them today. b. the bottom layer of the Earths crust. c. massive, irregularly-shaped slabs of solid rock. d. the basins that hold sea water.
• Slide 83
• POST-MODULAR QUESTIONS: 5.The word tectonics comes from a. the English word technical. b. the Latin word for deep. c. the physics term for sliding friction. d. The Greek word meaning to build.
• Slide 84
• POST-MODULAR QUESTIONS: 6.The number of plates that cover the Earths surface is approximately a. 12 b. 53 c. 128 d. 2012
• Slide 85
• POST-MODULAR QUESTIONS: 7.Most plates are a. mostly Oceanic. b. mostly Continental. c. partly Oceanic and partly Continental. d. neither Oceanic nor Continental.
• Slide 86
• POST-MODULAR QUESTIONS: 8.Heat from deep within the Earth rises toward the crust, causing the plates to move (very slowly) is due primarily to a. convection. b. conduction. c. radiation. d. subduction.
• Slide 87
• POST-MODULAR QUESTIONS: 9.The term for the geological process by which the edge of one plate slides under the edge of an adjacent plate is called a. crusting. b. abduction. c. transition. d. subduction.
• Slide 88
• POST-MODULAR QUESTIONS: 10.The phrase Continental Drift a. describes the actual movements of the continents over eons of time. b. is misleading, since the continents do not drift, the plates move. c. is a measure of the water flow patterns on the surface of the Earth. d. Is used to describe the motion of molten crust after an external impact.
• Slide 89
• POST-MODULAR QUESTIONS: 11.The Atlantic Ocean will a. open and close over cycles of 300 to 500 million years. b. eventually evaporate due to increased heat from the core of the Earth. c. In time drain into the major Atlantic Fault Line. d. remain much the same indefinitely.
• Slide 90
• POST-MODULAR QUESTIONS: 12.The frequencies of seismic waves passing between layers of the mantle and crust a. are mainly ultrasonic. b. are mainly infrasonic. c. are mainly with the human audio frequency range. d. are inaudible, since they do not generate sound waves.