Earth's Interior PDF

2.1. Earth's Interior www. c k 12.org 2.1 Earth's Interior FlexBooks 2.0 > Middle School Science (8) > Earth's Interior Last Modified: Oct 02, 2024 [Figure 1] How deep can we go into Earth's interior? Not very deep, that's...

2.1. Earth's Interior www. c k 12.org 2.1 Earth's Interior FlexBooks 2.0 > Middle School Science (8) > Earth's Interior Last Modified: Oct 02, 2024 [Figure 1] How deep can we go into Earth's interior? Not very deep, that's for sure! The deepest a drill hole has gotten was the Kola Superdeep Borehole. That hole got to 12,262 meters (40,230 feet), about one-third of the way into the crust in that area. So learning about what's deeper requires less direct methods. A few of these methods will be described in this concept. Learning About Earth’s Interior If someone told you to figure out what is inside Earth, what would you do? How could you figure out what is inside our planet? How do scientists figure it out? Seismic Waves Geologists study earthquake waves to “see” Earth's interior. Waves of energy radiate out from an earthquake’s focus. These waves are called seismic waves (Figure below). Seismic waves go different speeds through different materials. They change speed when they go from one type of material to another. This causes them to bend. Some seismic waves do not travel through liquids or gases. They just stop. Scientists use information from seismic waves to understand what makes up the Earth’s interior. 35 https://flexbooks.ck12.org/flx/b/27507190/68690192 2.1. Earth's Interior www. c k 12.org [Figure 2] The properties of seismic waves allow scientists to understand the composition of Earth's interior. Meteorites Scientists study meteorites to learn about Earth’s interior. Meteorites formed in the early solar system. These objects represent early solar system materials (Figure below). Some meteorites are made of iron and nickel. They are thought to be very similar to Earth's core. An iron meteorite is the closest thing to a sample of the core that scientists can hold in their hands! [Figure 3] This meteorite contains the mafic minerals olivine and pyroxene. It also contains metal flakes, similar to the material that separated into Earth’s core (metal) and mantle (ultramafic rock). Density 36 https://flexbooks.ck12.org/flx/b/27507190/68690192 2.1. Earth's Interior www. c k 12.org Earth’s overall density is higher than the density of crustal rocks, so the core must be made of something dense, like metal. Magnetic Field Since Earth has a magnetic field, there must be metal within the planet. Iron and nickel are both magnetic. Summary Different types of seismic waves behave differently in different materials. Their behavior can tell scientists about the material they travel through. Earth must contain metal. Its density, and the fact that it has a magnetic field, require it. Meteorites formed early in the solar system. They indicate something about Earth's interior. Review 1. How do scientists know that Earth's interior contains metal? 2. What do meteorites tell us about Earth's interior? 3. How do scientists use seismic waves to learn about Earth's interior? Explore More Use the resource below to answer the questions that follow. https://flexbooks.ck12.org/flx/render/embeddedobject/1478 37 https://flexbooks.ck12.org/flx/b/27507190/68690192 2.1. Earth's Interior www. c k 12.org 1. What types of waves do earthquakes produce? 2. What are the fastest body waves? 3. What is the shadow zone? 4. What do S-waves do? 5. List and explain the two types of surface waves. Report Content Errors 38 https://flexbooks.ck12.org/flx/b/27507190/68690192 2.2. Earth's Outer Layers www. c k 12.org 2.2 Earth's Outer Layers FlexBooks 2.0 > Middle School Science (8) > Earth's Outer Layers Last Modified: Oct 02, 2024 [Figure 1] Does this look familiar? Gases, water, rock, and living organisms are all found at Earth's surface. These materials are also found above or below the surface. They interact with each other and in doing so alter each other. For example, the hydrosphere may cause some of the lithosphere to wash away. Spheres Earth is made of layers. Since Earth is round, the layers all have the ending "-sphere" (Figure below). Some of the different parts of the Earth are the: Atmosphere: The thin layer of air, mostly nitrogen and oxygen, that surrounds the Earth. Hydrosphere: All the water on Earth. Biosphere: All the living organisms on Earth. 39 https://flexbooks.ck12.org/flx/b/27507190/68690193 2.2. Earth's Outer Layers www. c k 12.org Lithosphere: The solid rock part of Earth, including mountains, valleys, continents, and all of the rock beneath the oceans. [Figure 2] Earth has four layers: atmosphere, hydrosphere, biosphere, and lithosphere. All of Earth’s layers interact. Therefore, Earth’s surface is constantly undergoing changes. https://flexbooks.ck12.org/flx/render/embeddedobject/236601 Summary 40 https://flexbooks.ck12.org/flx/b/27507190/68690193 2.2. Earth's Outer Layers www. c k 12.org Earth is made of layers. The names end in sphere because Earth is round. Some of the layers are: atmosphere, biosphere, hydrosphere, and lithosphere. The lithosphere is the brittle crust and uppermost mantle. Review 1. What is the atmosphere? 2. What is the lithosphere? 3. Where is the hydrosphere? 4. How do Earth's layers interact? Give an example. Explore More Use the resource below to answer the questions that follow. https://flexbooks.ck12.org/flx/render/embeddedobject/58888 1. What are the four major systems of Earth? 2. What are the components of the geosphere? 3. What is the hydrosphere? 4. Where does Earth's energy come from? 5. What are ecosystems? 6. What is feedback? Report Content Errors 41 https://flexbooks.ck12.org/flx/b/27507190/68690193 2.2. Earth's Outer Layers www. c k 12.org 42 https://flexbooks.ck12.org/flx/b/27507190/68690193 2.3. Earth's Inner Layers www. c k 12.org 2.3 Earth's Inner Layers FlexBooks 2.0 > Middle School Science (8) > Earth's Inner Layers Last Modified: Oct 02, 2024 [Figure 1] What's below our feet? What's way below? If we could cut Earth open, we'd see the following layers from inside to outside: inner core, outer core, mantle, and crust. Alternatively, you can think of the brittle lithosphere riding on the plastic asthenosphere. Whew! Layers by Composition The layers scientists recognize are pictured below (Figure below). 43 https://flexbooks.ck12.org/flx/b/27507190/68690194 2.3. Earth's Inner Layers www. c k 12.org [Figure 2] A cross-section of Earth showing the crust, mantle, outer core, and inner core. The lithosphere includes the crust and uppermost mantle, and the asthenosphere sits just below the lithosphere. Core, mantle, and crust are divisions based on composition: 1. The crust is less than 1% of Earth by mass. The two types are oceanic crust and continental crust. 2. The mantle is hot, dense, dark (ultramafic) rock. It represents about 68% of Earth's mass. 3. The core is mostly iron metal. The core makes up about 31% of the Earth. Earth's metallic core has two layers: a solid inner layer and a liquid outer layer. The terms core, mantle, and crust will be described in more detail in the next three concepts. 44 https://flexbooks.ck12.org/flx/b/27507190/68690194 2.3. Earth's Inner Layers www. c k 12.org https://flexbooks.ck12.org/flx/render/embeddedobject/236602 Layers by Mechanical Properties Lithosphere and asthenosphere are divisions based on mechanical properties: 1. The lithosphere is composed of both the crust and the uppermost mantle. The lithosphere is a brittle, rigid solid. It is easily cracked or broken. 2. The asthenosphere is below the lithosphere. The asthenosphere is also in the upper mantle. This layer is solid, but it can flow and bend. A solid that can flow is like silly putty. Summary By composition, Earth is divided into core, mantle, and crust. By mechanical properties, the crust and upper mantle are divided into lithosphere and asthenosphere. The core-mantle-crust divisions are based on composition. The lithosphere-asthenosphere divisions are based on mechanical properties. Review 1. What are the the layers of Earth, based on composition? Where are they located? 2. What is the composition of the different layers? 3. How do the lithosphere and asthenosphere differ from each other? Explore More 45 https://flexbooks.ck12.org/flx/b/27507190/68690194 2.3. Earth's Inner Layers www. c k 12.org Use the resource below to answer the questions that follow. https://flexbooks.ck12.org/flx/render/embeddedobject/58890 1. What is the core? 2. Explain the core's structure. 3. What is the mantle? 4. What is the crust? 5. Why does the Earth have layers? Report Content Errors 46 https://flexbooks.ck12.org/flx/b/27507190/68690194 2.4. Earth's Crust www. c k 12.org 2.4 Earth's Crust FlexBooks 2.0 > Middle School Science (8) > Earth's Crust Last Modified: Oct 02, 2024 [Figure 1] What do these two photos have in common? Both of these photos are of Earth's crust. The crust on the left is on the continent. It's what you see and walk on every day. The crust on the right is in the ocean. You may have seen pictures, but to see it in person you need special equipment. Crust Crust, mantle, and core differ from each other in chemical composition. It's understandable that scientists know the most about the crust, and less about deeper layers. Earth’s crust is a thin, brittle outer shell. The crust is made of rock. This layer is thinner under the oceans and much thicker in mountain ranges. Oceanic Crust There are two kinds of crust. Oceanic crust is made of mafic lavas that flow onto the seafloor and is mainly basalt (Figure below). It is relatively thin, between 5 to 12 kilometers thick (3 - 8 miles). The rocks of the oceanic crust are denser (3.0 g/cm3) than the rocks that make up the continents. Thick layers of mud cover much of the ocean floor, which may eventually form sedimentary rock. 47 https://flexbooks.ck12.org/flx/b/27507190/68690195 2.4. Earth's Crust www. c k 12.org [Figure 2] Gabbro is a dark dense rock that can be found in oceanic crust. Continental Crust Continental crust is much thicker than oceanic crust. It is 35 kilometers (22 miles) thick on average, but it varies a lot. Continental crust is made up of many different rocks (Figure below). All three major rock types—igneous, metamorphic, and sedimentary—are found in continental crust, but the greatest proportion is made of felsic igneous rocks such as granite. On average, continental crust is much less dense (2.7 g/cm3) than oceanic crust. Since it is less dense, it rises higher above the mantle than oceanic crust. [Figure 3] The average composition of continental crust is granite. https://www.youtube.com/embed/ggrnN99CHCY 48 https://flexbooks.ck12.org/flx/b/27507190/68690195 2.4. Earth's Crust www. c k 12.org Summary Oceanic crust is thinner and denser than continental crust. Oceanic crust is darker in color and denser (more mafic). Continental crust is lighter in color and density (more felsic). Earth's crust is very thin relative to Earth's radius. Review 1. What are the properties of crust? 2. Describe the properties of oceanic crust. 3. Describe the properties of continental crust. Explore More Use this resource to answer the questions that follow. https://www.sciencemag.org/news/2018/09/watch-hurricane-put-dent-earth-s-crust 1. Where did Hurricane Harvey make landfall? How much water did it dump? 2. Where did the water go after the storm? 3. What happened to Earth’s crust? 4. How can scientists determine the weight of the water from Harvey? 5. What is depression of crust called? 6. Where did the water go after Harvey? 7. How long did it take for the water stored on land to dissipate? 8. Why will storms strike with increased frequency and ferocity? 9. What does the narrator’s mom always say? Report Content Errors 49 https://flexbooks.ck12.org/flx/b/27507190/68690195 2.5. Earth's Mantle www. c k 12.org 2.5 Earth's Mantle FlexBooks 2.0 > Middle School Science (8) > Earth's Mantle Last Modified: Oct 02, 2024 [Figure 1] What does mantle rock look like? You can't go to the mantle but small pieces of the mantle can come to you. Kimberlite forms deep in the mantle and is erupted violently into the crust. Kimberlite can contain diamonds. Most kimberlites reached the surface much earlier in Earth history. Mantle Beneath the crust is the mantle. The mantle is made of hot, solid rock. Scientists know this because of seismic waves, meteorites, and the heat that comes from inside the planet. Mantle rock is mostly peridotite, which is rich in iron and magnesium (Figure below). Peridotite is rare at Earth's surface. 50 https://flexbooks.ck12.org/flx/b/27507190/68690196 2.5. Earth's Mantle www. c k 12.org [Figure 2] The rock of the mantle is mostly peridotite. Peridotite is formed of crystals of olivine (green) and pyroxene (black). Heat Flow Through the process of conduction, heat flows from warmer objects to cooler objects (Figure below). The lower mantle is heated directly by conduction from the core. In conduction, heat is transferred as atoms collide. Hot lower mantle material rises upward. As it rises, it cools. At the top of the mantle, it moves horizontally. Over time it becomes cool and dense enough that it sinks. Back at the bottom of the mantle, it travels horizontally. Eventually, the material gets to the location where warm mantle material is rising. The rising and sinking of warm and cooler material is called convection. 51 https://flexbooks.ck12.org/flx/b/27507190/68690196 2.5. Earth's Mantle www. c k 12.org [Figure 3] The lower mantle is heated by conduction from the core. Heat then flows through the mantle by convection 52 https://flexbooks.ck12.org/flx/b/27507190/68690196 2.5. Earth's Mantle www. c k 12.org https://flexbooks.ck12.org/flx/render/embeddedobject/188816 Summary The mantle is composed of solid peridotite. Conduction from the core heats the lower mantle. Mantle convection brings hot material up toward the surface. It brings cooler material down toward the core. Review 1. How do scientists know what the mantle is made of? 2. What is conduction? 3. How does convection work in the mantle? Explore More Use this resource to answer the questions that follow. 53 https://flexbooks.ck12.org/flx/b/27507190/68690196 2.5. Earth's Mantle www. c k 12.org https://flexbooks.ck12.org/flx/render/embeddedobject/236603 1. In which ocean did researchers try to drill into the mantle in 1961? In 2016? 2. How much of Earth is made of mantle? 3. Where in the ocean would you have the best chance of drilling to the mantle? 4. Why did the researchers stop drilling in 1961? 5. What noteworthy sample did researchers bring to the surface in 2016? 6. What happens at the Moho discontinuity? 7. What are extremophiles? Where do they live? 8. How deep did the drilling go in 2016? How deep do they hope to get? 9. What do scientists hope to find? Why would that sort of thing be found inside Earth? Report Content Errors 54 https://flexbooks.ck12.org/flx/b/27507190/68690196 2.6. Earth's Core www. c k 12.org 2.6 Earth's Core FlexBooks 2.0 > Middle School Science (8) > Earth's Core Last Modified: Oct 02, 2024 [Figure 1] Is this what the core looks like? Yes! The outer core, anyway. The outer core is liquid metal, like in this photo. Of course, the metal is under an incredible amount of pressure. Core The dense, iron core forms the center of the Earth. Scientists know that the core is metal. The inner core is solid, and the outer core is molten. Here are some of the reasons they know this: Metallic meteorites are thought to be from the same type of material that is found at the core (Figure below). 55 https://flexbooks.ck12.org/flx/b/27507190/68690197 2.6. Earth's Core www. c k 12.org [Figure 2] An iron meteorite is the closest thing to the Earth’s core that we can hold in our hands. Scientists calculate Earth's density from the planet's rotation. To match the total density, the inner layers must be denser than the outer layers. They must be as dense as metal. Seismic waves show that the outer core is liquid. The inner core is solid. For there to be a magnetic field, there must be liquid metal. The metal must be convecting. If the core did not have convecting metal, there would be no magnetic field. https://www.youtube.com/embed/YxGgkF582rI Summary Density calculations show that Earth's core is metal. Seismic waves show that the inner core is solid and the outer core is liquid. 56 https://flexbooks.ck12.org/flx/b/27507190/68690197 2.6. Earth's Core www. c k 12.org Metallic meteorites and the magnetic field are also clues about the makeup of the core. Review 1. What evidence is there that Earth's core is metal? 2. What evidence is there that the outer core is molten? 3. Why does Earth have a magnetic field? Explore More Use this resource to answer the questions that follow. https://flexbooks.ck12.org/flx/render/embeddedobject/236604 1. What layers does the core have within it according to the study described in this video? 2. How deep is the core? What is its temperature? 3. What clues to researchers use to “see” what is in Earth’s interior? 4. What was the inner core thought to be previously? 5. What do scientists now think is inside the core? How big is it? 6. What is the interior made of? How do scientists know this is different from the material outside of it? 7. How are crystals aligned in the inner inner and outer inner cores? 8. Why is this information important? Report Content Errors 57 https://flexbooks.ck12.org/flx/b/27507190/68690197 2.6. Earth's Core www. c k 12.org 58 https://flexbooks.ck12.org/flx/b/27507190/68690197 2.7. Lithosphere and Asthenosphere www. c k 12.org 2.7 Lithosphere and Asthenosphere FlexBooks 2.0 > Middle School Science (8) > Lithosphere and Asthenosphere Last Modified: Oct 02, 2024 [Figure 1] Can you think of a solid that can flow? You use one twice a day! Toothpaste is a solid that can flow. Is the asthenosphere made of toothpaste? Only if the toothpaste is ultramafic in composition, and then it would only be able to flow if it were really, really hot. Still, the toothpaste analogy gives you a good image of how the asthenosphere might behave if you squeezed it Lithosphere The lithosphere is composed of both the crust and the portion of the upper mantle that behaves as a brittle, rigid solid. The lithosphere is the outermost mechanical layer of the Earth. The lithosphere is about 100 kilometers thick. How are crust and lithosphere different from each other? The definition of the lithosphere is based on how Earth materials behave, so it includes the crust and the uppermost mantle, which are both brittle. Since it is rigid and brittle, when stresses act on the lithosphere, it breaks. This is what we experience as an earthquake. Although we sometimes refer to Earth's plates as being plates of crust, the plates are actually made of lithosphere. Much more about Earth's plates follows in the chapter "Plate Tectonics." Asthenosphere The asthenosphere is the next mechanical layer. It consists of the solid upper mantle material that is so hot that it behaves plastically and can flow. The lithosphere rides on the 59 https://flexbooks.ck12.org/flx/b/27507190/68690198 2.7. Lithosphere and Asthenosphere www. c k 12.org asthenosphere. Because the asthenosphere can flow, it bends and deforms instead of breaking under stress. Summary The lithosphere is the brittle crust and uppermost mantle. The asthenosphere is a solid but it can flow, like toothpaste. The lithosphere rests on the asthenosphere. Review 1. Where is the lithosphere? What layers does it include? 2. What is the asthenosphere? 3. How do the lithosphere and asthenosphere differ? 4. If the lithosphere is resting on the asthenosphere and you put a lot of weight on the lithosphere, say ice in a glacier, how would the lithosphere respond? Explore More Use this resource to answer the questions that follow. https://flexbooks.ck12.org/flx/render/embeddedobject/236605 1. Where is the crust? What is it made of? 2. How thin is the crust? 60 https://flexbooks.ck12.org/flx/b/27507190/68690198