This Document Contains Chapters 1 to 4 Chapter 1 Introduction to Earth Science The chapter Introduction to Earth Science opens by listing and describing what sciences comprise the encompassing heading of Earth science. These include geology, oceanography, meteorology, astronomy, and environmental science. It goes on to introduce the concept of scales of space and time. The nature of scientific inquiry is discussed. The chapter explains the origins and creation of the Earth and solar system while noting the differences in how the inner and outer planets formed. Earth’s four major spheres are addressed. These spheres are the hydrosphere, atmosphere, biosphere, and geosphere. The chapter looks at Earth’s internal structure from both a physical properties and a chemical composition point of view. This leads to the concept of plate tectonics and a brief introduction to plate boundary types. A quick overview of the difference between major continental features and major oceanic features follows. The chapter wraps up by discussing how and why Earth is a system, citing examples of feedback loops and how people interact with the Earth system. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 1.1 List and describe the sciences that collectively make up Earth science. Discuss the scales of space and time in Earth science. 1.2 Discuss the nature of scientific inquiry and distinguish between a hypothesis and a theory. 1.3 Outline the stages in the formation of our solar system. 1.4 List and describe Earth’s four major spheres. 1.5 Label a diagram that shows Earth’s internal structure. Briefly explain why the geosphere can be described as being mobile. 1.6 List and describe the major features of the continents and ocean basins. 1.7 Define system and explain why Earth is considered to be a system. STRATEGIES FOR TEACHING EARTH SCIENCE Chapter 1 is meant to be an introductory chapter. Use this chapter to highlight topics in which you have particular expertise or that you expect to cover in more detail throughout the course. Since it is meant to be an overview of Earth science, avoid the pitfall of going into great detail about each topic at the beginning of your course when students are reading this chapter. Give students the general idea of what they will encounter during the course. It may be useful to point out which chapters explore particular topics in more detail for the coming weeks. • Pose the question, “What is Earth science?” Consider having students discuss this question with others seated near them and asking for collective answers. This is also a good icebreaker for the start of a course, so that students may meet others in the class. • Have students brainstorm, either individually or in small groups, ways that Earth science affects them. Have them think of how they impact the Earth. • Use a visual aid to help students grasp the concept of geologic time. Construct a toilet paper geologic time scale prior to class (see Additional Resources). This generates student interest and shows the vastness of geologic time in a concrete way. Alternatively, have students construct their own calculator tape time scale (also in Additional Resources) for a more interactive experience. • Make a list of statements where some are hypotheses and some are theories but don’t tell the students which are which. Present these to the class and have students make their own decisions about which statements are hypotheses and which are theories. Reveal the correct answers and discuss what makes a statement a hypothesis or a theory. Students retain the information better if they’ve tried to figure it out before you’ve actually presented it. • When discussing the origins of the solar system, stress the differences between the inner and outer planets; the inner planets are terrestrial whereas the outer planets are gaseous. • Before introducing Earth’s spheres, have students come up with lists of features that are naturally a part of Earth. They may be surprised at the things they did not think of (or did think of) as part of the study of Earth science. • Save the detailed discussion of Earth’s interior structure for later when it is covered in more detail in the book. However, it may be useful to bring a hardboiled egg and slice it in half. Use the analogy that the shell of the egg approximates the thickness of Earth’s crust, so that students see how thin a layer it is. • Introduce students to the idea that continental crust and oceanic crust are two different rock types. Ask students to describe some of the more notable features of continents and ocean basins. • Be sure to use visuals when describing introductory plate tectonics. At this stage illustrations and diagrams from the text should suffice. Video clips and animations will be useful later. • When introducing the concept that Earth is a system, have students come up with their own ideas of what constitutes a system. Relate a few of those ideas back to the Earth system, stressing the interconnectedness of everything. Teaching Strategy Summary for Chapter 1 Keep it basic and introductory. Give students a glimpse at the course ahead of them. Get students involved in thinking about concepts rather than just presenting the ideas as slides or notes. Students will feel more ownership over the course material if you give them opportunities to think about a topic before you lecture on it. CONCEPT CHECK ANSWERS Concept Check 1.1 1. List and briefly describe the sciences that collectively make up Earth science. Answer: • Geology – this is the study of the solid Earth. Physical geology examines the materials that comprise the Earth and historical geology aims to understand the origins and development of the planet. • Oceanography – examines the composition and dynamics of the world’s oceans. It also involves the study of coastal processes and seafloor topography as well as marine life. • Meteorology – this is the study of Earth’s atmosphere. It includes weather and climate. • Astronomy – this examines Earth as a body in space, both as part of the solar system and as part of a larger universe. • Environmental science – includes the study of natural resources, environmental hazards, and how people influence their environments and Earth processes. 2. Name the two broad subdivisions of geology and distinguish between them. Answer: • Physical geology – this is the study of the materials and processes that define the planet Earth. It includes the study of Earth’s composition, events such as volcanism, and the dynamics of Earth processes such as plate tectonics. • Historical geology – this is the study of the origins and evolution of Earth. It pieces together a chronological history of Earth based on clues in the rock record. These clues can include evidence of physical and biological changes throughout Earth’s 4.6 billion year history. 3. List at least four different natural hazards. Answer: • Earthquakes • Volcanoes • Floods • Tsunami • Hurricanes • Landslides 4. Aside from natural hazards, describe another important connection between people and Earth science. Answer: Humans influence Earth by altering its surface. People build cities and roads, and engineer projects that alter river flooding patterns. People pollute the air, the land, and the water, changing Earth from what is its natural state. 5. List two examples of size/place scales in Earth science that are at opposite ends of the spectrum. Answer: • A lightning flash happens within a fraction of a second but can instantly alter the immediate landscape. • Uplift of mountain ranges takes tens to hundreds of millions of years to occur. 6. How old is Earth? Answer: 4.6 billion years old. 7. If you compress geologic time into a single year, how much time has elapsed since Columbus arrived in the New World? Answer: 3 seconds. Concept Check 1.2 1. How is a scientific hypothesis different from a scientific theory? Answer: A hypothesis is an untested explanation for an observed phenomenon. It requires further observation or testing to see if it is valid. A theory is generally accepted by the scientific community as the best explanation for observable facts, as it has been subjected to rigorous scrutiny and tested repeatedly. 2. Summarize the basic steps followed in many scientific investigations. Answer: • An observation is made about the natural world. • Data surrounding that observation are collected. • A working hypothesis is developed. • More observations and/or experiments are performed to test the hypothesis. • The hypothesis is accepted, rejected, or modified. • Data and results are shared with the scientific community for critical analysis and further testing. Concept Check 1.3 1. Name and briefly outline the theory that describes the formation of our solar system. Answer: The nebular theory states that the early solar system originated as a cloud of dust and gas about 5 billion years ago as a star gravitationally collapsed. This rotating nebular cloud eventually contracted into a flattened, rotating disk. The cloud cooled and heavier metallic and rocky material condensed and accreted into the inner planets. The outer planets formed from residual gases and ices in the outer nebular cloud. 2. List the inner planets and the outer planets. Describe basic differences in size and composition. Answer: Inner planets: Mercury, Venus, Earth, and Mars. These planets are relatively small and rocky; they are made up largely of metals and silicate minerals. Outer planets: Jupiter, Saturn, Uranus, and Neptune. These planets are much larger than the inner planets and are composed of ices and gases. Concept Check 1.4 1. List Earth’s four spheres. Answer: • Atmosphere • Hydrosphere • Biosphere • Geosphere 2. Compare the height of the atmosphere to the thickness of the geosphere. Answer: The atmosphere is a very thin layer compared to the planet itself. The radius of the solid Earth is about 6400 km (4000 mi) whereas the entire atmosphere is roughly 160 km (100 mi) thick. 3. How much of Earth’s surface do oceans cover? How much of the planet’s total water supply do oceans represent? Answer: Oceans cover 70% of the planet. They account for 97% of Earth’s water supply. 4. To which sphere does soil belong? Answer: Geosphere Concept Check 1.5 1. List and briefly describe Earth’s compositional layers. Answer: • Crust – this is the outermost layer of Earth. It is very thin and made up of oceanic and continental types of crust. • Mantle – this is a semi-molten, relatively thick layer of Earth. It is divided into the upper and lower mantle and its semi-fluid state allows for plate tectonics. • Core – this is at the center of Earth. The inner core is solid nickel and iron, whereas the outer core is liquid. It is the thickest of all Earth’s structural layers. 2. Contrast the lithosphere and the asthenosphere. Answer: The lithosphere is the relatively cool, hard, outer shell of Earth’s crust. The asthenosphere is relatively soft and has some melting in its upper layer. The different natures of these two layers, which are in contact with each other, is what allows for plate tectonics, where the hard lithosphere moves on the semifluid upper portion of the asthenosphere. 3. What are lithospheric plates? List the three types of boundaries that separate plates. Answer: Lithospheric plates are the broken up slabs of Earth’s rigid outer shell, the lithosphere. The three types of plate boundaries are divergent, convergent, and transform fault. Concept Check 1.6 1. Contrast continents and ocean basins. Answer: Continents are made of granitic rocks whereas oceans are made of basaltic rocks. Continents are less dense and thicker than ocean basins. 2. Describe the general distribution of Earth’s youngest mountains. Answer: They are at the margins of continents. 3. What is the difference between shields and stable platforms? Answer: A shield is a large stable area of very old crystalline rock. A stable platform is a shield covered by sedimentary rock. 4. What are the three major regions of the ocean floor and some features associated with each region? Answer: • Continental margins – contains the continental shelf, the continental slope, and the continental rise. It is the boundary between continents and oceans. • Deep-ocean basins – these include the vast, flat abyssal plains of the ocean bottom. They also contain deep ocean trenches and seamounts in varied stages of erosion. • Oceanic ridges – these are divergent plate boundaries where new igneous rock is formed. These are vast winding ridges of underwater volcanic mountains that wind around the Earth. Concept Check 1.7 1. What is a system? List three examples of systems. Answer: A system is a group of interacting, independent parts that make up a complex whole. Examples of systems include a city transportation system, a weather system, or an automotive cooling system. 2. What are the two sources of energy for the Earth system? Answer: The Sun and Earth’s interior. 3. Predict how a change in the hydrologic cycle, such as increased rainfall in an area, might influence the biosphere and geosphere in that area. Answer: An increase in rainfall might affect the biosphere by changing the amount and types of vegetation found in that area. In turn, the vegetation change could alter the types of animals that inhabit the region. Increasing the rainfall could affect the geosphere by increasing erosion. Conversely, if vegetation increases also, the plants could be a stabilizing factor that decreases erosion. GIVE IT SOME THOUGHT ANSWERS 1. After entering a dark room, you turn on a wall switch, but the light does not come on. Suggest at least three hypotheses that might explain this observation. How would you determine which one of your hypotheses (if any) is correct? Answer: • There is a local power outage. • The light source (bulbs, tubes, etc.) is “burned out” and no longer working. • The electricity to the room is not turned on or has been disconnected. You can determine which of these is correct by testing the hypothesis. For example, you can replace the light bulb with a new one to see if it works. You can look at the circuit breakers and see if any of them are not on. You can call the electric company to see if service has been discontinued or if there are general power outages in your area. 2. Each of the following statements may either be a hypothesis (H), a theory (T), or an observation (O). Use one of these letters to identify each statement. Briefly explain each choice. a. A scientist proposes that a recently discovered large ring-shaped structure on the Canadian Shield is the remains of an ancient meteorite crater. b. The Redwall Formation in the Grand Canyon is composed primarily of limestone. c. The outer part of Earth consists of several large plates that move and interact with each other. d. Since 1885, the terminus of Canada’s Athabasca Glacier has receded 1.5 kilometers. Answer: a. Hypothesis – it is a tentative explanation b. Observation c. Theory – well tested and widely accepted by the scientific community d. Observation – direct measurement of how far the glacier has moved 3. Making accurate measurements and observations is a basic part of scientific inquiry. The accompanying radar image, showing the distribution and intensity of precipitation associated with a storm, provides one example. Identify another image in this chapter that illustrates a way in which scientific data are gathered. Suggest an advantage that might be associated with the example you select. Answer: Figure 1.7 shows a paleontologist collecting fossils. An advantage of fossil data is that it is concrete and observable. Fossils can be used to tell about the past climate of an area and they can be used to help determine the age of the rocks in which it was found, and the ages of surrounding rocks. 4. The length of recorded history for humankind is about 5000 years. Clearly, most people view this span as being very long. How does it compare to the length of geologic time? Calculate the percentage or fraction of geologic time that is represented by recorded history. To make calculations easier, round the age of Earth to the nearest billion. Answer: 5000/5,000,000,000= 0.000001% 5. Refer to the graph in Figure 1.13 to answer the following questions. a. If you were to climb to the top of Mount Everest, how many breaths of air would you have to take at that altitude to equal one breath at sea level? Answer: Air pressure at the top of Mount Everest is about 1/3 that at sea level, so you would need to take 3 breaths relative to sea level. b. If you are flying in a commercial jet at an altitude of 12 kilometers (about 39,000 feet), about what percentage of the atmosphere’s mass is below you? Answer: About 75% of the atmosphere’s mass is below you. 6. Examine Figure 1.12 to answer these questions. a. Where is most of Earth’s freshwater stored? Answer: Glaciers b. Where is most of Earth’s liquid freshwater found? Answer: Groundwater 7. Jupiter, the largest planet in our solar system, is 5.2 astronomical units (AU) from the Sun. How long would it take to go from Earth to Jupiter if you traveled as fast as a jet (1000 kilometers/hour)? Do the same calculation for Neptune, which is 30 AU from the Sun. Referring to the GEO graphics feature on page 15 will be helpful. Answer: 1 AU = 150 million km. 5.2 AU × 150,000,000 km = 780,000,000 km 780,000,000 km × hour/1000 km = 780,000 hrs = 32,500 days = 89 years Neptune: 30 AU × 150 million km = 4.5 billion km 4.5 billion km × hour/1000 km = 4,500,000 hours = 187,500 days = 513.7 years 8. These rock layers consist of materials such as sand, mud, and gravel that, over a span of millions of years, were deposited by rivers, waves, wind, and glaciers. Each layer was buried by subsequent deposits and eventually compacted and cemented into solid rock. Later, the region was uplifted, and erosion exposed the layers seen here. a. Can you establish a relative time scale for these rocks? That is, can you determine which one of the layers shown here is likely oldest and which is probably youngest? Answer: Based on the principle of superposition, where lower layers are older and upper layers are younger, the bottom-most layer is likely the oldest, and the uppermost layer is probably the youngest among the exposed rock layers. b. Explain the logic you used. Answer: The oldest rock is on the bottom and the youngest is on the top. Each layer was put down successively; therefore newer rock kept building upon the rock already in place. EXAMINING THE EARTH SYSTEM ANSWERS 1. This scene is in British Columbia’s Mount Robson Provincial Park. The park is named for the highest peak in the Canadian Rockies. a. List as many examples as possible of features associated with each of Earth’s four spheres. Answer: Geosphere – mountains, rock Biosphere – trees, vegetation on slopes Hydrosphere – lake, ice on mountain slope Atmosphere – sky, clouds b. Which, if any, of these features was created by internal processes? Describe the role of external processes in this scene. Answer: The mountains were created by internal processes. Earth’s internal heat engine is responsible for plate tectonics. Plate tectonics drives mountain building. External processes in this scene would include precipitation to create the lake and the water for the ice. Erosion would generate the soil for the trees to grow in. Erosion would also shape the rock features and mountains. Atmospheric temperature determines the state of matter of the water. 2. Humans are a part of the Earth system. List at least three examples of how you, in particular, influence one or more of Earth’s major spheres. Answer: Answers will vary. Examples could include driving a car and putting pollution in the atmosphere, living in a home heated by natural gas taken from the Earth, eating food that requires clearing of forests to create cropland. Three ways I influence Earth's major spheres include: 1. Atmosphere: Through activities like driving vehicles and using energy, I contribute to greenhouse gas emissions, affecting climate and air quality. 2. Hydrosphere: My consumption habits and waste disposal impact water quality and availability, particularly through plastic pollution and chemical runoff. 3. Lithosphere: Construction and land use changes alter the landscape and soil composition, influencing local ecosystems and geological processes. 3. The accompanying photo provides an example of interactions among different parts of the Earth system. It is a view of a debris flow (popularly called a mudslide) that was triggered by extraordinary rains. Which of Earth’s four spheres were involved in this natural disaster, which buried a small town on the Philippine island of Leyte? Describe how each contributed to or was influenced by the event. Answer: Geosphere – contains the soil that became mud flowing down the mountain. The geosphere is also part of the topography that created the mountain. Atmosphere – heavy rains fell during an atmospheric event. Biosphere – any vegetation growing on the slope or in the path of the mudslide will have been uprooted or destroyed. Hydrosphere – water that fell to the earth saturated the soil and became part of the hydrosphere. The hydrosphere also contained the water that was evaporated and eventually became the rainfall that triggered this event. 4. Examine the accompanying concept map that links the four spheres of the Earth system. All of the spheres are linked by arrows that represent processes by which the spheres interact and influence each other. For each arrow list at least one process. Answer: Atmosphere – Hydrosphere – Water evaporates from the hydrosphere into the atmosphere and water precipitates from the atmosphere to become part of the hydrosphere. Hydrosphere – Geosphere – The geosphere creates the topography in which lakes, rivers, and ocean basins can form. Geosphere – Biosphere – The geosphere contains the soil in which vegetation may grow. Biosphere – Atmosphere – Plants transpire moisture into the atmosphere and they respire oxygen into the atmosphere. Atmosphere – Geosphere – The atmosphere generates precipitation that can trigger erosion. Hydrosphere – Biosphere – The hydrosphere contains ground water that allows growth of vegetation. DISCUSSION TOPICS • Why study Earth science? Answer: Studying Earth science helps us understand the planet's processes, resources, and natural hazards, which are crucial for sustainable living and effective environmental stewardship. It provides insights into Earth's history, climate changes, and the interconnectedness of its systems, guiding informed decision-making for the future. • Do you think the scientific method is an exact recipe that scientists follow or more of a set of guidelines for investigation? Explain your reasoning. Answer: The scientific method is more of a set of guidelines for investigation rather than an exact recipe. It provides a structured approach to inquiry, but scientists often adapt and refine methods based on specific research questions, contexts, and available technology, allowing for flexibility and creativity in scientific exploration. • Why do we make a distinction between the different “spheres” of Earth? Answer: We distinguish between Earth's spheres (atmosphere, hydrosphere, lithosphere, biosphere) to better study and understand the complex interactions and processes that occur within each sphere and across boundaries. This helps in comprehending environmental dynamics, resource management, and the impacts of human activities on the planet more effectively. • What do Earth scientists mean when they speak of change as a constant? Answer: When Earth scientists refer to change as a constant, they mean that Earth's systems and processes are continuously evolving and undergoing natural fluctuations over various timescales. This perspective acknowledges that environmental conditions, geological formations, and biological communities are always in flux, driven by both natural and human-induced factors. • Why is it important to recognize Earth as a system? When can it be more relevant to study individual parts of the system? Answer: Recognizing Earth as a system helps understand interconnected processes and feedback loops crucial for addressing global issues like climate change and resource management. Studying individual parts becomes relevant for detailed analysis or localized impacts, such as studying a specific ecosystem or geological formation's unique characteristics or responses to change. ADDITIONAL RESOURCES DVDs or Movies • How the Earth Was Made (2008) Narrated by Alec Baldwin. History Channel, 1 hour 34 minutes • Inside Planet Earth (2008) Narrated by Patrick Stewart. Discovery Channel, 2 hours. • Earth Revealed, Episode 1: Down to Earth (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/series78.html Websites • Evolution of Our Solar System – Framework for an interactive classroom activity where students learn the order of events that created the solar system. http://www.lpi.usra.edu/education/timeline/activity/ • Earth Science Picture of the Day – Various pictures that can open up discussion in the classroom. http://epod.usra.edu • Toilet Paper Geologic Time Scale – Directions for creating a visual time scale analogy for a class demonstration. http://serc.carleton.edu/quantskills/activities/TPGeoTime.html • Calculator Tape Time Scale – Similar to the toilet paper time scale except students do the calculations and create the time scale themselves. http://serc.carleton.edu/quantskills/activities/calculatortape.html Chapter 2 Matter and Minerals Matter and Minerals begins with an explanation of what defines a mineral by listing the characteristics one looks for when determining if something is a mineral. It continues to describe what defines a rock and briefly compares and contrasts rocks versus minerals. The chapter continues with a discussion of atoms and how elements are the building blocks of minerals. Parts of an atom are discussed and the periodic table of the elements is introduced in the context of mineralogy. Atomic bonding is examined as a lead in to discussing mineral properties. The various properties that define a mineral are presented in detail. These properties include luster, color, light transmittance, streak, crystal shape or habit, hardness, cleavage, fracture, tenacity, and specific gravity. After discussing these introductory concepts, the chapter identifies the various mineral groups, differentiating between silicate and nonsilicate minerals. The most abundant elements from the periodic table are presented as the major constituents of Earth’s crust. The structure and other properties of major silicate minerals are shown, and the names of these minerals are presented. A distinction is made between light and dark silicates and the reasons for these color variations. Important nonsilicate minerals are then presented. There is a brief discussion of natural resources, and mineral resources are examined in this context. Economics of minerals and mineral extraction methods end this chapter. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 2.1 List the main characteristics that an Earth material must possess to be considered a mineral and describe each. 2.2 Compare and contrast the three primary particles contained in atoms. 2.3 Distinguish among ionic bonds, covalent bonds, and metallic bonds. 2.4 List and describe the properties that are used in mineral identification. 2.5 List the common silicate and nonsilicate minerals and describe the characteristics of each group. 2.6 Discuss Earth’s natural resources in terms of renewability. Differentiate between mineral resources and ore deposits. TEACHING TIPS Chapter 2 contains what, for many students, is a great deal of new information coupled with a lot of new vocabulary. Pace yourself and be sure any new information, such as mineral names and characteristics, are presented clearly. Having lots of hand samples as visual aids retains student interest as well as helps you to illustrate your points. Much of what there is to learn about minerals is visual so visuals are very important for this chapter in particular. • If you discuss the periodic table, atoms, and bonding, be sure to make references to how these topics relate to minerals. Students tend to think of these topics as being “chemistry” so giving them a relationship to Earth science will keep these concepts fresh and give students a different perspective. • When explaining the difference between a mineral and a rock, have a large hand sample of something that is clearly a mineral, e.g. feldspar, and a hand sample of a rock that clearly is an aggregate of minerals, e.g. granite. This helps illustrate how minerals can be constituents of rocks or rocks in and of themselves. • You can simultaneously introduce the concepts of mineral cleavage and internal bonding by bringing to class a large hand sample of a readily and obviously cleaved mineral such as halite, calcite, or feldspar. Also bring a rock hammer and safety goggles. Show how when hit with a hammer, the mineral cleaves along consistent planes. Use this to explain how it reflects patterns of weak atomic bonding within the mineral. • Students often confuse the crystal form of quartz for cleavage, when quartz only exhibits fracture. If you have a quartz sample to spare, you might hit it with a rock hammer to demonstrate fracture and reinforce the fact that crystal form and cleavage are two very different things, but both are a reflection of internal atomic structure. • If you do not have the capacity to demonstrate fracture or cleavage in your classroom, consider using short YouTube video clips where these properties are demonstrated by others. • If your course has a laboratory component, leave the heavy duty teaching and memorization of mineral names to the lab. In the laboratory, students will have several hours with hands-on access to the samples and be able to observe the minerals’ properties for themselves while associating them with names. • Whether or not your course has a laboratory component, consider bringing examples of minerals to class. When illustrating different properties, select classic examples of minerals that show these properties. For example: • Metallic luster – galena • Streak – chalk or hematite • Hardness – scratch glass with quartz and scratch talc with a fingernail. Challenge a student to try to scratch glass with talc or some other soft mineral. • Crystal form – halite or quartz • When discussing the 8 most abundant elements in Earth’s crust, it can be useful to show this list in conjunction with a Periodic Table so that students can see how very few elements are responsible for what we know of as Earth. • Some students are already familiar with some gemstones. Framing minerals in the context of gems that they may know can be useful for some. • Before you talk about natural resources, have students in groups or individually look around them and try to determine what things in the room or building might have been extracted from the Earth. Quartz clocks and watches, silicon in computers, and metals used to construct various items are a few of the things they may come up with. Teaching Strategy Summary for Chapter 2 Use lots of visual aids. Either engage students in hands-on interaction with minerals or prepare demonstrations of the various qualities associated with minerals. CONCEPT CHECK ANSWERS Concept Check 2.1 1. List two characteristics an Earth material must have in order to be considered a mineral. Answer: • Naturally occurring • Generally inorganic • Solid • Orderly crystalline structure • Definite chemical composition. 2. Define the term rock. How do rocks differ from minerals? Answer: Rocks are more loosely defined as aggregates of different minerals. Rocks differ from minerals because they may be of varied mineral content and they may contain nonmineral matter. Concept Check 2.2 1. List the three main particles of an atom and explain how they differ from one another. Answer: • Proton – positively charged particle in the nucleus of the atom. The number of protons is the same as the element number. • Neutron – particle in the nucleus of the atom. It has no charge associated with it. • Electron – negatively charged particle that orbits the nucleus. There are the same number of electrons as protons in a given element. 2. Make a simple sketch of an atom and label its three main particles. Answer: See Figure 2.4. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in energy levels or shells. 3. What is the significance of valence electrons? Answer: The valence shell of an atom is its outermost shell and responsible for bonding with other atoms. The electrons of the valence shell are those that are shared with other atoms in the bonding process. Concept Check 2.3 1. What is the difference between an atom and an ion? Answer: An atom does not have a charge because it has an equal number of protons or electrons. Ions have either given up or taken on more electrons, giving the ion a positive or negative charge. 2. What occurs in an atom to produce a positive ion? A negative ion? Answer: An atom that has given up one or more valence electrons becomes a positive ion. An atom that has taken on extra valence electrons becomes a negative ion. 3. Briefly distinguish among ionic, covalent, and metallic bonding and describe the role that electrons play in each. Answer: • Ionic bonding – one atom “donates” its electrons to another, creating two ions bonded to each other. • Covalent bonding – two atoms equally share valence electrons. • Metallic bonding – several atoms contribute their valence electrons to a pool of electrons that are free to move through the entire structure. Concept Check 2.4 1. Define luster. Answer: Luster describes the quality of light reflected from a mineral’s surface. It may be metallic or nonmetallic, with several subdistinctions among nonmetallic lusters. 2. Why is color not always a useful property in mineral identification? Give an example of a mineral that supports your answer. Answer: There may be small impurities in the mineral that will alter its color. Quartz is a notable example, with rose quartz (pink) and amethyst (purple) being only two examples of color variants. 3. What differentiates cleavage from fracture? Answer: Cleavage occurs when a mineral breaks cleanly along a plane. This is due to a plane of weak atomic bonding within the mineral. Fracture occurs when there is no distinct plane along which the mineral can break; when hit with a rock hammer, the mineral will fracture into irregular pieces. 4. What do we mean when we refer to a mineral’s tenacity? List three terms that describe tenacity. Answer: Tenacity is a mineral’s resistance to cutting, breaking, and other forms of deformation. Three terms that describe tenacity are brittle, malleable, and sectile. Elastic is another term. 5. What simple chemical test is useful in the identification of the mineral calcite? Answer: Putting a drop of weak acid, such as HCl, on the mineral will create a visible reaction with bubbling on the surface. Concept Check 2.5 1. List the eight most common elements in Earth’s crust, in order of abundance (most to least). Answer: Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium. 2. Explain the difference between silicon and silicate. Answer: Silicon is an element. Silicates contain silicon and oxygen and are the major constituents of continental crust. 3. Draw a sketch of the silicon-oxygen tetrahedron. Answer: See Figure 2.23. A silicon-oxygen tetrahedron consists of a silicon atom at the center with four oxygen atoms bonded to it, forming a tetrahedral structure. Each oxygen atom shares two electrons with the silicon atom, creating a stable tetrahedral shape commonly found in silicate minerals like quartz and feldspar. 4. What is the most abundant mineral in Earth’s crust? Answer: Feldspar. The most abundant mineral in Earth's crust is feldspar. Feldspar comprises approximately 60% of the Earth's crust by weight and is a group of rock-forming minerals that includes potassium feldspar, sodium feldspar, and calcium feldspar. 5. List six common nonsilicate mineral groups. What key ion(s) or element(s) define each group? Answer: • Carbonates – CO3 ion • Halides – F, Cl, Br • Oxides – O • Sulfides – S • Sulfates – SO4 ion • Native elements – various single elements such as gold and copper. 6. What is the most common carbonate mineral? Answer: Calcite 7. List eight common nonsilicate minerals and their economic uses. Answer: • Calcite – Portland cement, lime • Halite – salt • Fluorite – steelmaking • Hematite – Ore of iron • Galena – Ore of lead • Sphalerite – Ore of zinc • Chalcopyrite – Ore of copper • Silver – Jewelry Concept Check 2.6 1. List three examples of renewable resources and three examples of nonrenewable resources. Answer: • Renewable – solar, forests and trees, water • Nonrenewable – Metals, oil, coal 2. Compare and contrast a mineral resource and an ore deposit. Answer: Mineral resources are occurrences of useful minerals in such large amounts that extraction is reasonably certain. An ore deposit is a naturally occurring concentration of one or more minerals with economic value. Mineral resources include deposits that are not economically viable to recover where ore deposits are. 3. Explain how a mineral deposit that previously could not be mined profitably might be upgraded to an ore deposit. Answer: Demand for a metal may increase its value or technological advances may make it more profitable to extract the metal than previously. GIVE IT SOME THOUGHT ANSWERS 1. Using the geologic definition of mineral as your guide, determine which of the items in this list are minerals and which are not. If something in this list is not a mineral, explain. Answer: a. mineral – gold is an example of a mineral classified as a native element; b. seawater is not a mineral – minerals by definition are solids; c. quartz is a mineral; d. cubic zirconia is not a mineral – it is not naturally occurring; e. obsidian is not a mineral because it lacks an internal arrangement of atoms, however, it is an igneous rock; f. ruby is a mineral – it is a gemstone variety of the mineral corundum; g. glacial ice is a mineral as it meets all of the criteria; h. amber is not a mineral since it has an organic origin. 2. Assume that the number of protons in a neutral atom is 92 and its mass number is 238. a. What is the element? b. How many electrons does it have? c. How many neutrons does it have? Answer: a. The element is uranium. b. 92 electrons c. 146 neutrons 3. Which of the following elements is more likely to form chemical bonds: xenon (Xe) or sodium (Na)? Explain why. Answer: Sodium is more likely to form chemical bonds because of its tendency to lose one electron, resulting in an overall +1 charge. 4. Referring to the accompanying photos of five minerals, determine which of these specimens exhibit a metallic luster and which have a nonmetallic luster. Answer: Specimens A, B, and D have a nonmetallic luster. Specimens C and E have a metallic luster. 5. Gold has a specific gravity of almost 20. A 5-gallon bucket of water weighs 40 pounds. How much would a 5-gallon bucket of gold weigh? Answer: 5 gallons of water = 40 lbs. × 20 (specific gravity of gold) = 800 lbs. 6. Examine the accompanying photo of a mineral that has several smooth, flat surfaces that resulted when the specimen was broken. a. How many flat surfaces are present on this specimen? b. How many different directions of cleavage does this specimen have? c. Do the cleavage directions meet at 90-degree angles? Answer: a. 6 b. 3 c. no 7. Each of the following statements describes a silicate mineral or mineral group. In each case, provide the appropriate name. a. The most common member of the amphibole group b. The most common light-colored member of the mica family c. The only common silicate mineral made entirely of silicon and oxygen d. A silicate mineral with a name that is based on its color e. A silicate mineral that is characterized by striations f. A silicate mineral that originates as a product of chemical weathering Answer: a. Hornblende b. Muscovite c. Quartz d. Rose quartz e. Feldspar f. Calcite 8. What mineral property is illustrated in the accompanying photo? Answer: Cleavage. 9. Do an Internet search to determine what minerals are extracted from the ground during the manufacture of the following products. a. Stainless steel utensils b. Cat litter c. Tums brand antacid tablets d. Lithium batteries e. Aluminum beverage cans Answer: a. Stainless steel utensils: Chromium, nickel, iron, and possibly other alloying elements like manganese and carbon. b. Cat litter: Bentonite (clay minerals) or silica gel (silica minerals). c. Tums brand antacid tablets: Calcium carbonate. d. Lithium batteries: Lithium (extracted from lithium-containing minerals like spodumene or lithium salts). e. Aluminum beverage cans: Bauxite (aluminum ore). 10. Most states have designated a state mineral, rock, or gemstone to promote interest in the state’s natural resources. Describe your state mineral, rock, or gemstone and explain why it was selected. If your state does not have a state mineral, rock, or gemstone, complete the exercise by selecting one from a state adjacent to yours. Answer: My state, California, has designated gold as its state mineral due to its historical significance during the Gold Rush era, which played a pivotal role in the state's development and economy. DISCUSSION TOPICS • What are some renewable and non-renewable resources you use regularly? Answer: I regularly use renewable resources like solar energy (for electricity) and wind energy (indirectly through grid power). Nonrenewable resources include fossil fuels such as gasoline (for transportation) and natural gas (for heating). • How many of the elements of the Periodic Table have you used or encountered? How many of those elements are one of the 8 major constituents of Earth’s crust? Answer: I have encountered or used approximately 30 elements from the Periodic Table. Of those, around 6 elements (oxygen, silicon, aluminum, iron, calcium, sodium) are among the 8 major constituents of Earth's crust. • Why do you think a mineral has to be non-organic? Answer: Minerals are defined as naturally occurring inorganic substances with a specific chemical composition and crystal structure. The term "non-organic" emphasizes that minerals form through geological processes involving inorganic chemical reactions, distinct from the biological processes that create organic compounds. • Why do you think a mineral has to be naturally occurring to be classified as a mineral? Answer: A mineral must be naturally occurring to distinguish it from synthetic or man-made substances. This criterion ensures minerals originate from geological processes rather than being artificially created in a laboratory, maintaining the distinction between natural geological formations and human-made materials. • What are some minerals you use regularly? Answer: Some minerals I use regularly include: 1. Quartz: Found in electronics (silicon dioxide) and kitchen countertops (quartzite). 2. Calcite: Used in construction materials like cement and in calcium supplements (calcium carbonate). ADDITIONAL RESOURCES DVDs or Movies • Rocking Around the Silicates, Performed by Richard Alley, Penn State University, 4 minutes, 23 seconds. http://www.youtube.com/watch?v=utypgC7h6f4 • Earth Revealed, Episode 12: Minerals: The Materials of Earth (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/ series78.html Websites • Name that Atom Interactive Game. http://www.learner.org/interactives/periodic/basics_interactive.html • Online Mineral Identification – Contains pictures of minerals. Students decide which properties to “test” to identify the mineral. http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/ minerals/ • Mineral Identification Key – From the Mineralogical Society of America. Takes the student step by step through the identification process for a sample that the student has in his/her possession. http://www.minsocam.org/msa/collectors_corner/id/mineral_id_keyq1.htm • Online Mineral Museum – Comprehensive listing of minerals with pictures, chemical formulas, and where they are commonly found. http://www.johnbetts-fineminerals.com/museum.htm • The Dynamic Earth from the Smithsonian Institution’s National Museum of Natural History – Choose “Gems and Minerals” Interactive exhibit where students can learn about mineral growth and formation, and about gemstones. Highlights specimens found at the museum in Washington, D.C. but also a good stand-alone website for learning. http://www.mnh.si.edu/earth/main_frames.html Chapter 3 Rocks: Materials of the Solid Earth Rocks: Materials of the Solid Earth opens with a discussion of the rock cycle that presents a general overview of the origins and processes involved in forming the three major rock groups—igneous rock, sedimentary rock, and metamorphic rock. A discussion of the crystallization of magma is followed by an examination of the classification, textures, and compositions of igneous rocks. After presenting the processes of mechanical and chemical weathering, the chapter discusses the classification of sedimentary rocks, as well as some of their common features. The chapter also examines the agents of metamorphism, the textural and mineralogical changes that take place during metamorphism, and some common metamorphic rocks. In conclusion, resources from rocks and minerals are investigated. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 3.1 Sketch, label, and explain the rock cycle. 3.2 Describe the two criteria used to classify igneous rocks and explain how cooling influences the crystal size of minerals. 3.3 List and describe the different categories of sedimentary rocks and discuss the processes that change sediment into sedimentary rock. 3.4 Define metamorphism, explain how metamorphic rocks form, and describe the agents of metamorphism. 3.5 Distinguish between metallic and nonmetallic mineral resources and list at least two examples of each. Compare and contrast the three traditional fossil fuels. TEACHING TIPS Students should have a good grasp on minerals before attempting this chapter. Much of the discussion of rock composition relies on understanding the basics of the minerals that make up the rocks. As with mineralogy, it is useful to have handy in class hand samples of the various rocks so students have a tangible way of relating your notes to the actual rocks. After introducing students to the three basic rock types, it is useful to have them construct their own rock cycles in their notes without consulting any other information. In this way they need to understand why and how the rock cycle works the way it does, and they will retain the information better. If your course has a laboratory component, consider leaving the memorization of different rock types for the lab. In the lab, students will have more and longer access to actual rock specimens and can explore their properties firsthand. Regardless of whether or not your course has a lab, bring hand samples that exemplify different rock types to class so students can see what the actual rocks look like. Sometimes students have difficulty seeing granite as a felsic rock because it has dark minerals in it. It can be useful to show several varieties of granite along with a chart depicting the rough percentages of light and dark colored minerals present in this rock. Ask students why they think most fossils are found in sedimentary rocks before explaining it to them. It doesn’t occur to many students that the magma that forms igneous rocks and the heat and pressure that shape metamorphic rocks are not conducive to fossilization. Have students list as many resources from rocks and minerals as they can think of before you teach this topic. Many students think of coal or oil but are surprised to learn drywall comes from gypsum, for example. When teaching about the types of oil traps, diagrams are critical. Descriptions of these environments alone are tricky for students to understand. Have students in groups or individually think of analogies from their lives for the three different rock types. For example, making a sandwich could be analogous to the deposition of sedimentary strata. Relating these concepts to students’ everyday lives can help improve retention. CONCEPT CHECK ANSWERS Concept Check 3.1 Sketch and label the rock cycle. Make sure your sketch includes alternative paths. Answer: Refer to Figure 3.1. The rock cycle involves processes like weathering, erosion, sedimentation, metamorphism, melting, and solidification, illustrating how rocks can transform between igneous, sedimentary, and metamorphic types through various pathways. Use the rock cycle to explain the statement “One rock is the raw material for another.” Answer: The rock cycle illustrates that any rock type can be transformed into any other rock type. As an example, igneous rocks may be weathered and compacted into sedimentary rocks. Those sedimentary rocks may be subjected to heat and pressure to become metamorphic rocks. Depending upon the conditions, rocks can be continually transformed into different types of rock. Concept Check 3.2 What is magma? How does magma differ from lava? Answer: Magma is liquid, molten rock. It is found underground, whereas lava is found extrusively, or outside Earth’s interior. In what basic settings do intrusive and extrusive igneous rocks originate? Answer: Intrusive igneous rocks cool below the surface of the Earth. Extrusive igneous rocks cool outside the Earth’s interior. How does the rate of cooling influence crystal size? What other factors influence the texture of igneous rocks? Answer: Faster cooling correlates with smaller crystal size. Other influential factors include the composition of the magma and the presence of gases, such as in a volcano, that can cause a vesicular texture. What does a porphyritic texture indicate about the history of an igneous rock? Answer: A porphyritic texture, where the rock has some large and some small crystals, indicates that the rock started to cool slowly and then experienced a change of environment or cooling temperature where the rest of the rock cooled more quickly. List and distinguish among the four basic compositional groups of igneous rocks. Answer: Granitic – felsic or light colored rocks where the dominant minerals are quartz and potassium feldspar. Andesitic – intermediate rocks where the dominant minerals are amphibole and plagioclase. These are neither light nor dark. Basaltic – mafic or dark colored rocks with high amounts of magnesium and/or iron. The dominant minerals are pyroxene and plagioclase feldspar. Ultramafic – these are uncommon rocks with very high amounts of magnesium and/or iron. The dominant minerals are olivine and pyroxene. How are granite and rhyolite different? In what way are they similar? Answer: Granite has a phaneritic, or coarse-grained texture whereas rhyolite is aphanitic, or fine-grained. They are compositionally similar, being granitic or felsic rocks. They could be from the same magma type but rate of cooling has affected their crystal sizes. What is magmatic differentiation? How might this process lead to the formation of several different igneous rocks from a single magma? Answer: Magmatic differentiation occurs as magma cools and crystals of minerals with higher melting temperatures crystallize out of the magma, changing the magmatic composition. By depleting the magma, or melt, of these minerals, the next rocks to form from the cooling magma will have a different composition than those that formed at higher temperatures. Concept Check 3.3 Why are sedimentary rocks important? Answer: Sedimentary rocks contain almost all of the fossil record. Sedimentary rocks make up about 75% of continental rock outcrops and contain clues to the history of the Earth’s surface. They also have economic importance; for example coal is a sedimentary rock and other natural resources are extracted from sedimentary rocks. What minerals are most abundant in detrital sedimentary rocks? In which rocks do these sediments predominate? Answer: Quartz and clay minerals, especially from feldspars, are most abundant. These rocks predominate in conglomerate, breccia, sandstone, arkose, siltstone, and shale. Distinguish between conglomerate and breccia. Answer: Both are made of large sized sedimentary grains. However, conglomerate consists of grains that have been rounded before compaction and breccia contains angular grains of rock and minerals. What are the two categories of chemical sedimentary rock? Give an example of a rock that belongs to each category. Answer: Chemical and biochemical. A chemical sedimentary rock is travertine limestone. Another is chert. A biochemical rock is coquina or coal. How do evaporites form? Give an example. Answer: Evaporites form when minerals are dissolved in solution, and the water of that solution evaporates away. One example is rock salt. Describe the two processes by which sediments are transformed into sedimentary rocks. Which is the most effective process in the lithification of sand and gravel-sized sediments? Answer: • Compaction occurs where pressure is placed on loosely packed sediment. Volume of the sediment is reduced and water is squeezed out. Cementation occurs when mineral-bearing water circulates among the grains, hardens, and cements the sediment grains together. This process is most effective for lithifying sand and gravel-sized sediments. List three common cements. How might each be identified? Answer: • Calcite – effervesces when a drop of weak HCl is placed on it. Silica – hardest cement, will scratch glass. Iron oxide – oxidizes to a rusty red color. What is the most characteristic feature of sedimentary rocks? Answer: Layers, or strata as these rocks are laid down. Concept Check 3.4 Metamorphism means “change form.” Describe how a rock may change during metamorphism. Answer: Mineralogy, texture, and sometimes chemical composition may change. Intense heat and/or pressure will alter the grains of the original rock, whether it is igneous, sedimentary, or metamorphic. Briefly describe what is meant by the statement “every metamorphic rock has a parent rock.” Answer: Metamorphic rocks are existing rocks that have been altered by heat and/or pressure. Therefore, every metamorphic rock was another type of rock, the parent rock, initially. List the four agents of metamorphism and describe the role of each. Answer: • Heat – triggers chemical reactions that result in recrystallization of existing minerals and formation of new minerals. Confining pressure – buried rocks experience even pressure from all directions, which creates a more compact, denser rock. Differential stress – often occurs during mountain building where rocks experience unequal forces from different directions. This creates rocks that have been deformed, often with flattened mineral grains. Chemically active fluids – ion-rich fluids invade the rock and enhance ion migration. Often hot, these fluids can generate mineral recrystallization. Distinguish between regional and contact metamorphism. Answer: Regional metamorphism is associated with mountain building and involves large amounts of pressure and high temperatures. It results in large-scale rock deformation. Contact metamorphism occurs when rock is in contact with hot magma. In these cases, metamorphism is heat-related. What feature easily distinguishes schist and gneiss from quartzite and marble? Answer: Schist and gneiss are foliated. In what ways do metamorphic rocks differ from the igneous and sedimentary rocks from which they formed? Answer: Metamorphic rocks are typically more compact than the parent igneous and sedimentary rocks. Metamorphic rocks may also exhibit minerals aligned in one particular direction rather than randomly dispersed in the rock. Minerals also may segregate during metamorphism. Concept Check 3.5 List two general types of hydrothermal deposits. Answer: Vein deposits and disseminated deposits. Nonmetallic resources are commonly divided into two broad groups. List the two groups and give some examples of materials that belong to each. Answer: Building materials – aggregate, crushed rock, gypsum, clay, and limestone. Industrial minerals – fluorite, limestone, corundum, garnet, sylvite. Why are coal, oil, and natural gas called fossil fuels? Answer: These are all created from organisms that lived long ago. In the case of coal, it is lithified plant matter, for example. What is an oil trap? Sketch two examples. Answer: An oil trap is a geologic environment that allows for significant amounts of oil and gas to accumulate. See Figure 3.35 for pictures of examples. An oil trap is a geological formation that prevents the upward migration of oil and gas, typically due to structural or stratigraphic features. Examples include anticlines (folded rock structures) and fault traps (where fault movement creates impermeable barriers). What do oil traps have in common? Answer: Porous, permeable reservoir rock and a cap rock that is impermeable to oil and gas. GIVE IT SOME THOUGHT ANSWERS Refer to Figure 3.1. How does the rock cycle diagram—in particular, the labeled arrows—support the fact that sedimentary rocks are the most abundant rock type on Earth’s surface? Answer: The rock cycle supports the fact that sedimentary rocks are most abundant on Earth’s surface because each rock type, once exposed at the surface, is subjected to uplift, weathering, and erosion. The resulting sediment will eventually be transformed into sedimentary rock. Would you expect all the crystals in an intrusive igneous rock to be the same size? Explain why or why not. Answer: No. Crystal size in igneous rocks is a direct function of the rate of cooling and since a given body of magma could experience differential rates as it cools and solidifies, different sizes of crystals in the same rock would be common. Apply your understanding of igneous rock textures to describe the cooling history of each of the igneous rocks pictured on the right. Answer: A) Rapid rate of cooling resulting in mainly microscopic crystals; B) a very slow rate of cooling followed by a more rapid period of cooling as evidenced by the porphyritic texture; C) relatively slow, steady rate of cooling resulting in larger crystals of about the same size; D) extremely rapid rate of cooling as indicated by the glassy texture. Is it possible for two igneous rocks to have the same mineral composition but be different rocks? Support your answer with an example. Answer: Yes, rhyolite and granite are a good example of two rocks with similar compositions. Rapid cooling of lava results in the aphanitic texture typical of rhyolite while granite exhibits large, visible crystals due to slow cooling of magma. Use your understanding of magmatic differentiation to explain how magmas of different composition can be generated in a cooling magma chamber. Answer: Remember that Bowen’s Reaction Series not only predicts the sequence of crystallization for minerals from magmas, but it also provides the order in which those minerals will melt as temperature increases for a given rock. If only partial melting (as opposed to complete melting) occurs, the resulting magma will only contain those chemical elements from the minerals whose melting temperatures have been achieved. Therefore, the magma could have a significantly different chemical composition than the original rock. In addition, varying degrees of partial melting could produce several different magmatic compositions from the original rock. Dust collecting on furniture is an everyday example of a sedimentary process. Provide another example of a sedimentary process that might be observed in or around where you live. Answer: The accumulation of organic debris (leaves, stems, branches, etc.) and physical debris (mud, soil, etc.) around your home and in your yard are other examples of sedimentary processes. Describe two reasons sedimentary rocks are more likely to contain fossils than igneous rocks. Answer: One reason why sedimentary rocks are more likely to contain fossils is because sediment accumulates in various environments (oceans, lakes, rivers, beaches, swamps, deserts, etc.) where both plants and animals already exist. As the organisms die, they accumulate with detrital sediments and often become incorporated into the final rock that is formed. Another reason is that the various processes involved in the formation of sedimentary rocks (erosion, deposition, and lithification) are often not so destructive as to obliterate the original form or at least some part of the original organism. If you hiked to a mountain peak and found limestone at the top, what would that indicate about the likely geologic history of the rock there? Answer: The geologic history of the limestone layer would perhaps be the following: 1) formation of marine limestone in a warm, shallow ocean; 2) burial and lithification of limestone over a long period of time; 3) uplift of unit, most likely related to plate tectonic forces at or near a plate boundary; 4) erosion of younger units and exposure of limestone layer at the top of a present-day mountain. The accompanying photos each illustrate either a typical igneous, sedimentary, or metamorphic rock body. Which do you think is a metamorphic rock? Explain why you ruled out the other rock bodies. Answer: Outcrop “B” is composed of metamorphic rock. Photograph “A” shows layers of sediment and coarse layers of gravel typical of sedimentary rocks. Photograph “C” displays an igneous rock with some sort of intrusion cutting through it. Also, photograph “B” shows highly banded rock layers with intense folding and kink banding, typical of metamorphic rocks. Examine the accompanying photos, which show the geology of the Grand Canyon. Notice that most of the canyon consists of layers of sedimentary rocks, but if you were to hike down into the Inner Gorge, you would encounter the Vishnu Schist, which is metamorphic rock. What process might have been responsible for the formation of the Vishnu Schist? How does this process differ from the processes that formed the sedimentary rocks that are atop the Vishnu Schist? What does the Vishnu Schist tell you about the history of the Grand Canyon prior to the formation of the canyon itself? Why is the Vishnu Schist visible at Earth’s surface? Is it likely that rocks similar to the Vishnu Schist exist elsewhere but are not exposed at Earth’s surface? Explain. Answer: a) The Vishnu Schist could have formed from regional metamorphism involving increased temperatures and pressures associated with plate tectonics. This is a very different process from the various steps involved in the formation of the sedimentary rocks above it (weathering, erosion, deposition, and lithification). b) The Grand Canyon obviously had a much different geologic history involving regional metamorphism and perhaps various episodes of mountain building compared the modern erosion of the Colorado River. c) The Vishnu Schist has been exposed at Earth’s surface due to uplift and the erosion of this region by the Colorado River. d) Yes, it is very likely that the Vishnu Schist exists in other areas since such rocks are typically formed by regional metamorphism (which takes place over large regions). It simply has not been exposed in most other areas. EXAMINING THE EARTH SYSTEM ANSWERS The sedimentary rock coquina, shown at right, formed in response to interactions among two or more of Earth’s spheres. List the spheres associated with the formation of this rock and write a short explanation for each of your choices. Answer: The sedimentary rock coquina is a biochemical limestone that consists of loosely cemented shells and shell fragments that have accumulated on the ocean floor. The primary Earth spheres involved in its formation are the biosphere, hydrosphere, and atmosphere (the source of the carbon dioxide for the mineral calcite found in the shells). Shale, a detrital sedimentary rock, is composed primarily of clay, a product of weathering of several different minerals, and possibly some organic matter. The spheres involved in its formation are the biosphere, hydrosphere (where the sediment accumulates), atmosphere (which is involved in the weathering process), and solid earth (which supplied the material to weather into clay). Of the two main sources of energy that drive the rock cycle—Earth’s internal heat and solar energy—which is primarily responsible for each of the three groups of rocks found on and within Earth? Explain your reasoning. Answer: Igneous and metamorphic rocks are associated with Earth’s internal heat. Sedimentary rocks, because they often contain organic matter and form in the sea, where the Sun is the energy source that drives waves and currents, are allied with both solar energy and Earth’s internal heat. Every year about 20,000 pounds of stone, sand, and gravel are mined for each person in the United States. Calculate how many pounds of stone, sand, and gravel will be needed for an individual during an 80-year lifespan. If 1 cubic yard of rocks weighs roughly 1700 pounds, calculate (in cubic yards) how large a hole must be dug to supply an individual with 80 years’ worth of stone, sand, and gravel? A typical pickup truck can carry about a half cubic yard of rock. How many pickup truck loads would be necessary during the 80-year span? Answer: 20,000 pounds/year × 80 years = 1,600,000 pounds. If a cubic yard of rock weighs roughly 1700 pounds, the volume of rock that would be mined over 80 years is 1,600,000 pounds ÷ 1700 pounds = 941.2 cubic yards. 1 cubic yard = 27 cubic feet, so 941.2 cubic yards × 27 cubic feet/cubic yard = 25,412 cubic feet. This is the equivalent of a hole approximately 28.5 feet wide, 28.5 feet long, and 28.5 feet deep. 941.2 cubic yards/½ cubic yard per pickup load = 1882 pickup loads. DISCUSSION TOPICS What types of rocks exist near you? Answer: Near me, common rock types include granite (igneous), limestone (sedimentary), and schist (metamorphic). Why do different sedimentary rocks exist in different places? Answer: Different sedimentary rocks exist in different places due to variations in depositional environments, such as oceans, rivers, lakes, and deserts, which result in diverse sediment compositions and structures over time. Why are there different types of granite? Answer: Different types of granite exist due to variations in mineral composition and formation conditions during their crystallization from molten magma deep within the Earth's crust. What would be a “real life” analogy to metamorphism? Answer: A "real life" analogy to metamorphism is the process of clay turning into ceramic pottery under high heat and pressure, altering its physical and chemical properties without melting. Why do we find very old rocks at Earth’s surface in some places but younger rocks at the surface in other places? Answer: Old rocks are exposed at the surface in some places due to tectonic activity like uplift and erosion, while younger rocks are at the surface in other areas where recent geological processes or deposition have occurred, covering older formations. What are some of the advantages and disadvantages of using fossil fuels? Answer: Advantages: Fossil fuels provide abundant and reliable energy sources that are currently integral to global infrastructure. Disadvantages: They contribute significantly to air pollution, greenhouse gas emissions, and environmental degradation, while their extraction can have detrimental impacts on local ecosystems. ADDITIONAL RESOURCES DVDs and Movies Sedimentary Rock Formation – short video that demonstrates how clastic sedimentary rocks form. Annenberg Media, 3 minutes, 18 seconds. Free streaming video at http://www.learner.org/series/modules/express/pages/scimod_07.html Earth Revealed, Episode 14: Intrusive Igneous Rocks (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/ series78.html Earth Revealed, Episode 17: Sedimentary Rocks: The Key to Past Environments (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/series78.html Earth Revealed, Episode 18: Metamorphic Rocks (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/series78.html Websites Rocks at Earth’s Surface – from the Smithsonian National Museum of Natural History. Interactive program describing rock formation and changes over time. http://www.mnh.si.edu/earth/ main_frames.html Igneous Rock Gallery – clear pictures showing textures and features of common igneous rocks. http://geology.com/rocks/igneous-rocks.shtml Sedimentary Rock Gallery – good pictures showing common sedimentary rocks. http://geology.com/ rocks/sedimentary-rocks.shtml Metamorphic Rock Gallery – clear pictures of common metamorphic rocks and their features. http://geology.com/rocks/metamorphic-rocks.shtml Ultimate Rock Quiz – from Discovery Channel online. Test your knowledge of rocks. http://www.discovery.com/tv-shows/curiosity/topics/rock-quiz.htm Personal Energy Use Calculator – How much fossil fuel do you use? http://environment.nationalgeographic.com/environment/energy/great-energy-challenge/ personal-energy-meter/ Chapter 4 Weathering, Soil, and Mass Wasting Weathering, Soil, and Mass Wasting begins with a brief examination of the external processes of weathering, mass wasting, and erosion. The two forms of weathering, mechanical and chemical, are investigated in detail —including the types, conditions, rates, and net effect of each. The soils section of the chapter begins with a description of the general composition, texture, and structure of soil. After the factors that influence soil formation, development, and classification are examined, soil erosion, as well as some ore deposits produced by weathering, are presented. Mass wasting begins with a look at the role the process plays in landform development. Following a discussion of the controls and triggers of mass wasting, a general presentation of the various types of mass wasting concludes the chapter. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 4.1 List three types of external processes and discuss the role each plays in the rock cycle. 4.2 Define weathering and distinguish between the two main categories of weathering. 4.3 Summarize the factors that influence the type and rate of rock weathering. 4.4 Define soil and explain why soil is referred to as an interface. 4.5 List and briefly discuss five controls of soil formation. 4.6 Sketch, label, and describe an idealized soil profile. 4.7 Explain the need for classifying soils. 4.8 Discuss the detrimental impact of human activities on soil and some ways that soil erosion is controlled. 4.9 Discuss the role that mass wasting plays in the development of landforms. 4.10 Summarize the factors that control and trigger mass-wasting processes. 4.11 List and explain the criteria that are commonly used to classify mass-wasting processes. 4.12 Distinguish among slump, rockslide, debris flow, and earthflow. 4.13 Contrast creep and solifluction. STRATEGIES FOR TEACHING WEATHERING, SOIL, AND MASS WASTING To help students understand the concept of increased surface area contributing to increased weathering, bring in two 5-pound bags of potatoes. One bag should contain a few large potatoes and the other should contain many small potatoes. Ask students which they would prefer to peel if they had to. Most will pick the bag of larger potatoes because there is less to peel. Explain that this is analogous to increased surface area in rocks; smaller potatoes have more surface area and therefore more peel. Smaller chunks of rock have more exposed surface area and more available weathering surfaces. Fill a jar partway with various sizes and shapes of small rocks of different varieties. Fill the rest of the jar with clean water. Put a lid with a tight seal on the jar and pass it around the class as you discuss weathering. Have each student shake the jar in turn. When the jar is returned to you, show how the once-clear water is now murky from bits of rock being “weathered” and “eroded” by the water and impact of being shaken. Fill a glass bottle with water and show it to the class and let them know you are going to put it in a freezer. Freeze the bottle overnight until the glass shatters. Bring the shattered bottle (carefully) to your next class to show how frost wedging can work in rocks. Put a small piece of limestone in a jar of vinegar or even a clear soda. Bring it to successive classes to show how even weak acids will erode a rock. Differential weathering results in many spectacular rock formations. Students often enjoy looking at pictures of many of these features from different places in the world. If you have an auger and permission to locally make a hole, bring students outside to witness the local soil profile. Alternatively, you can take a picture of a local soil profile and have students try to identify layers in it. Using the map in Figure 4.18, have students individually or in groups determine what type of soil they live on. Have them apply what they know about the local climate, bedrock, and other factors to why this might be true. Have students determine if their local region is at risk for landslides and have them determine why or why not. When describing the different types of mass wasting, it is helpful for students to be able to visually recognize what you are discussing. Use diagrams such as Figure 4.30 to illustrate the points you make about these events, but elaborate on what is in the picture. CONCEPT CHECK ANSWERS Concept Check 4.1 List examples of Earth’s external and internal processes. Answer: External processes – weathering, mass wasting, and erosion. Internal processes – mountain building, volcanic activity. From where do these processes derive their energy? Answer: External processes derive their energy from the Sun, while internal processes derive their energy from Earth’s interior. Concept Check 4.2 When a rock is mechanically weathered, how does its surface area change? How does this influence chemical weathering? Answer: Mechanical weathering increases the surface area of a rock by physically breaking it down. This leaves more of the surface available for chemical weathering processes. Explain how water can cause mechanical weathering. Answer: Water in its liquid form can cause mechanical weathering if it is running water by wearing down the surface of the rock. Water can also freeze and cause frost wedging; as water freezes in rock cracks, it expands, breaking up the rock. How does an exfoliation dome form? Answer: When large amounts of igneous rock that formed deep underground are exposed by erosion, a process called sheeting occurs, where concentric slabs break loose. This is partially due to the reduction in pressure the rock is under at the surface. As the overlying rock is eroding in a process called unloading, it generates an exfoliation dome. How does biological activity contribute to weathering? Answer: Plant roots can grow into rock fractures and further break it apart. Burrowing animals may also break down the rock. Other organisms such as fungi and lichen can produce acids that decompose the rock, and some bacteria also rely on rocks for nutrients, resulting in rock breakdown. How is carbonic acid formed in nature? What products result when carbonic acid reacts with potassium feldspar? Answer: Carbonic acid is formed when carbon dioxide dissolves in water. This can occur in the atmosphere and when water percolates through soil. Clay minerals are the most common result when carbonic acid reacts with potassium feldspar. Explain how angular masses of rock often become spherical boulders. Answer: Spheroidal weathering occurs as angular rock masses have their joints extensively invaded by water. Chemical weathering decomposes minerals in the rock and expands the joints, and rocks are eroded more on corners. The result is a smooth, rounded rock. Concept Check 4.3 Why did the headstones in Figure 4.9 weather so differently? Answer: They are made of different rock types with different mineral composition. Different minerals and rocks weather at different rates. How does climate influence weathering? Answer: Temperature and moisture affect chemical weathering rates, with more humidity and higher temperatures causing higher rates of weathering. Areas with low freeze–thaw cycle occurrences also do not tend to see as much, or any, frost wedging. Concept Check 4.4 Why is soil considered an interface in the Earth system? Answer: It is a common boundary where different parts of a system interact; in this case soil occurs where the geosphere, the atmosphere, the hydrosphere, and the biosphere all interact with each other. How is regolith different from soil? Answer: Regolith is only broken down rock and mineral matter whereas soil also contains organic matter, water, and air. Why is texture an important soil property? Answer: Texture is important because it influences the soil’s ability to retain water and air, both of which are critical to plant growth. Using the soil texture diagram in Figure 4.13, name the soil that consists of 60 percent sand, 30 percent silt, and 10 percent clay. Answer: Sandy loam. Concept Check 4.5 List the five basic controls of soil formation. Answer: Parent material, time, climate, plants and animals, and topography. Which factor is most influential in soil formation? Answer: Climate. How might the direction a slope is facing influence soil formation? Answer: If a slope receives more sunlight, such as on a south-facing slope in the Northern Hemisphere, the soil on it will be warmer and less moist, which will influence the types of vegetation that can grow in the soil as well as the nature of the soil itself. Concept Check 4.6 Sketch and label the main soil horizons in a well-developed soil profile. Answer: Refer to Figure 4.16.A well-developed soil profile typically includes horizons labeled as O (organic matter), A (topsoil), E (eluviated horizon), B (subsoil), and C (parent material). Describe the following features or processes: eluviation, leaching, zone of accumulation, and hardpan. Answer: Eluviation – washing out of finer soil particles by water trickling through. Leaching – depletion of soluble minerals from upper soil layers. Zone of accumulation – the B horizon, where much of what is washed out of the E horizon is deposited. Hardpan – very compact layer of clay that can form in the B horizon. Concept Check 4.7 Why are soils classified? Answer: Soils are classified because there is a large variety of soil types between different places and different times. Soil classification helps soil scientists identify common characteristics in soils. Refer to Figure 4.18 and identify three particularly extensive soil orders that occur in the contiguous 48 United States. Describe two soil orders that occur in Alaska. Answer: Contiguous United States: Aridisols, Mollisols, and Utilisols Alaska: Gelisols – young soils with little vertical development. Develop in areas with permafrost. Inceptisols – well-developed young soils with initial stages of soil development. Develop in humid regions. Concept Check 4.8 Link these phenomena in a description of soil erosion: sheet erosion, gullies, raindrop impact, rills, stream. Answer: Raindrop impact exerts force on the top layer of soil, mobilizing it. Flowing water forms thin sheets that move the soil; this is called sheet erosion. Tiny channels called rills form after this sheet layer has been flowing a short distance, and eventually deeper channels called gullies are created. As the soil particles are washed out, they move downslope into a stream. How have human activities affected the rate of soil erosion? Answer: Farming, logging, and construction all disturb the vegetation that stabilizes the soil. The soil is then more susceptible to erosion. Briefly describe three methods of controlling soil erosion. Answer: Creating terraces, or flat areas to grow crops on steep slopes, reduces the slope and soil erosion. Planting crops parallel to slope contours can reduce erosion on less steep slopes. Grassed waterways prevent the formation of gullies and trap soil washed from croplands. Concept Check 4.9 Discuss the meaning of the term landslide. Answer: A landslide is a geologic hazard where large amounts of rock and soil slide down steep slopes. What is the controlling force of mass wasting? Answer: Gravity. In what environment are rapid mass-wasting processes most likely to occur? Answer: Geologically young mountains with steep slopes that are rapidly eroded by rivers and glaciers. Sketch or describe how mass wasting contributes to the development of a valley. Answer: Running water produces stream valleys, but running water cuts very narrow channels. Mass wasting contributes weathered soil and rock downslope, enabling a wider valley. Concept Check 4.10 How does water affect mass-wasting processes? Answer: Water fills soil pores, making it more mobile. This allows gravity to more easily pull soil down a slope. Describe the significance of the angle of repose. Answer: The angle of repose is the steepest angle at which soil materials will remain stable. This angle varies by particle size and shape. Larger particles that are more angular will be stable at higher angles than smaller, more rounded particles. How might a forest fire influence mass wasting? Answer: Forest fires can destroy the vegetation on a slope. Vegetation acts to stabilize soil; removal of this stabilizing factor can cause mass wasting on the slope. Link earthquakes to landslides. Answer: Earthquakes can trigger landslides by dislodging large volumes of rock and unconsolidated soils on a slope. Concept Check 4.11 What terms describe the way material moves during mass wasting? Answer: Slumps, rockslides, debris flow, earthflow. Why can rock avalanches move at such great speeds? Answer: As rocks tumble down a slope, air can become trapped and compressed under the falling debris; this allows the rock avalanche to move as a buoyant, flexible sheet. Concept Check 4.12 Without looking at Figure 4.31A, sketch and label a simple cross section (side view) of a slump. Answer: See Figure. A slump is characterized by a concave-shaped landform where a mass of rock and soil has moved downslope, leaving a steep scarp or cliff at the head and a bulging toe at the base. Both slumps and rockslides move by sliding. How do these processes differ from one another? Answer: Slumps occur along a curved surface and generally do not carry material fast or far. Rockslides are mostly rock and occur when blocks of bedrock break loose and slide down a slope. Usually rock slides occur where rock strata are inclines or where joints and fractures parallel the slope. What factors contributed to the massive rockslide at Gros Ventre, Wyoming? Answer: Heavy rains, melting glacier, and a tilted sandstone bed no longer able to maintain its position on a saturated clay bed. How is a lahar different from a debris flow that might occur in southern California? Answer: Lahars are mostly volcanic materials that happen when layers of ash and debris are saturated with water, often from melted ice on a volcanic mountaintop. Flows in semiarid regions such as southern California occur when sudden rain or melting mountain snows mobilize soil. Lack of vegetation in semiarid climates contributes to the debris flow because the soil is not stabilized. Contrast earthflows and debris flows. Answer: Debris flows generally occur in channels in semiarid regions. Earthflows usually form on hillsides in humid areas following times of heavy rainfall or snowmelt. Concept Check 4.13 Describe the basic mechanisms that contribute to creep. Answer: Alternate expansion and contraction of surface material caused by a freeze/thaw cycle or wetting/drying. During what season does solifluction occur? Explain why it occurs only during that time of year. Answer: Solifluction only occurs during summer because the top layer of permafrost thaws and becomes what is known as the active layer. The active layer becomes saturated and cannot penetrate the underlying still frozen layer; thus the active layer slowly flows. GIVE IT SOME THOUGHT ANSWERS Describe how plants promote mechanical and chemical weathering but inhibit erosion. Answer: Plant roots in search of minerals and water grow into fractures and help to wedge rocks apart. Also, certain plants, fungi, and lichens produce acids or other compounds that aid in the chemical weathering of earth materials. However, the root systems of plants serve to inhibit erosion by binding and helping to hold soils and rocks in place. Granite and basalt are exposed at Earth’s surface in a hot, wet region. Will mechanical weathering or chemical weathering predominate? Which rock will weather more rapidly? Why? Answer: Chemical weathering would be much more important than mechanical weathering in a hot, wet climate. The moisture and higher temperatures would promote the various reactions involved in chemical weathering. When comparing granite vs. basalt in such an environment, basalt would probably weather more rapidly. Ferromagnesian minerals would be rapidly oxidized and decomposed under these conditions, and basalts have much larger percentages of these minerals than granite. The accompanying photo shows Shiprock, a well-known landmark in the northwestern corner of New Mexico. It is a mass of igneous rock that represents the “plumbing” of a now-vanished volcano. Extending toward the upper left is a related wall-like igneous structure known as a dike. The igneous features are surrounded by sedimentary rocks. Explain why these once deeply buried igneous features now stand high above the surrounding terrain. What term from Section 4.3, “Rates of Weathering,” applies to this situation? Answer: This is an example of differential weathering. The sedimentary rocks are less resistant to weathering and erosion and therefore were worn away more readily than the igneous rocks. Although once buried deeply, erosion over time has worn down the surrounding landscape, causing the less-weathered igneous structure to stand tall above the region. The accompanying photo shows a footprint on the Moon left by an Apollo astronaut in material popularly called lunar soil. Does this material satisfy the definition we use for soil on Earth? Explain why or why not. You may want to refer to Figure 4.12. Answer: Lunar soil does not meet the definition of soil that we use here on Earth. Soil is defined as being comprised of approximately 25% water, 25% air, 5% organic material, and 45% mineral matter. Of those components, only the mineral matter would be found on the Moon, thus not meeting the geologic definition of soil. What might cause different soils to develop from the same kind of parent material or similar soils to form from different parent materials? Answer: Different soils could develop from the same parent material if the rates and types of chemical weathering were dramatically different from one area to another. Such differences would be caused by different climates – for example a hot, wet climate would produce much more intense chemical weathering than a dry, cold climate. For the same reasons, different parent materials could also produce similar soils given the necessary climatic characteristics. Using the map of global soil regions in Figure 4.18, identify the main soil order in the region adjacent to South America’s Amazon River (point A on the map) and the predominant soil order in the American Southwest (point B). Briefly contrast these soils. Do they have anything in common? Referring to Table 4.2 might be helpful. Answer: The soils adjacent to the Amazon River basin are oxisols while the American Southwest is characterized by aridisols. Oxisols develop in tropical climates where leaching predominates, and they are enriched in iron and aluminum oxides. Aridisols are found in arid regions where water is not available to remove soluble materials, and they are enriched in calcium carbonate and salts. The only thing the two soil orders have in common is that they are both poor soils for agricultural activity. This soil sample is from a farm in the Midwest. From which horizon was the sample most likely taken— A, E, B, or C? Explain. Answer: This was most likely from the A horizon. It is dark and appears to be rich in organic matter. It is loosely consolidated, indicating a good volume of air. In addition, the A horizon is the layer plants would be likely to grow in on a farm. The concept of external and internal processes was introduced at the beginning of the chapter. In the accompanying photo, external processes are clearly active. Describe the role that mass wasting is playing. Identify one feature that is a result of mass wasting. Answer: Mass wasting is actively moving rock debris down the steep slopes of the canyon walls. The talus slopes along the base of the canyon wall on the right side of the photograph are evidence that active mass wasting is occurring. Describe at least one situation in which an internal process might cause or contribute to a mass wasting process. Answer: Active uplift of a region due to the internal processes of plate tectonics and mountain building could lead to mass wasting events. The uplifted areas could experience earthquakes or over steepened slopes, both of which could cause mass wasting to occur. Mass wasting is influenced by many processes associated with all four spheres of the Earth system. Select three items from the list below. For each, outline a series of events that relate the item to various spheres and to a mass-wasting process. Here is an example which assumes that “frost wedging” is an item on the list: Frost wedging involves rock (geosphere) being broken when water (hydrosphere) freezes. Freeze–thaw cycles (atmosphere) promote frost wedging. When frost wedging loosens a rock on a cliff, the fragment tumbles to the base of the cliff. This event, called a rockfall, is an example of mass wasting. Now you give it a try. Use your imagination. a. Wildfire Spring thaw/melting snow Highway road cut Crashing waves Cavern formation (see Figure 5.40) Answer: Answers will vary significantly. An example of wildfires would be: Wildfires destroy vegetation (biosphere) which removes the anchoring system of a slope and leads to increased mass wasting. The removal of vegetation by wildfires also allows water (hydrosphere) to better infiltrate the rocks and soil (geosphere) of a slope, thus increasing the likelihood of downslope movements. A slump is a type of mass wasting where a mass of rock and soil moves downslope along a curved surface, forming a distinctive concave-shaped landform with a steep headscarp and a toe that bulges outward at the base. EXAMINING THE EARTH SYSTEM ANSWERS Because of the burning of fossil fuels such as coal and petroleum, the level of carbon dioxide (CO2) in the atmosphere has been increasing for more than 150 years. Should this increase tend to accelerate or slow down the rate of chemical weathering of Earth’s surface rocks? Explain how you arrived at your conclusion. Answer: Increasing levels of carbon dioxide should ultimately result in higher levels of carbonic acid. Therefore, chemical weathering, which is primarily accomplished by carbonic acid, should also increase. Discuss the interaction of the atmosphere, geosphere, biosphere, and hydrosphere in the formation of soil. Answer: Soil is an interface where different parts of the Earth system interact. It forms where the solid Earth, the atmosphere, the hydrosphere, and the biosphere meet. Over time, the material of soil develops in response to complex environmental interactions among the different parts of the Earth system. The solid Earth and biosphere supply the mineral and organic materials of soil; the atmosphere along with the biosphere and hydrosphere furnish the acids and water to weather the material; and the atmosphere, biosphere, and hydrosphere help mix, transport, and sort the materials. The aerial view at right shows landslide debris atop Buckskin Glacier in Denali National Park in the rugged Alaska Range. Where Buckskin Glacier ends, its meltwater feeds a river that flows into Cook Inlet, just west of Anchorage. Cook Inlet is an arm of the North Pacific. Many processes have been responsible for creating this scene. Prepare a brief outline or summary to explain the formation and evolution of this landscape. Include internal and external processes and be sure to mention which spheres of the Earth system were involved. Answer: Precipitation, an external process and part of the atmosphere, created the glacier and the snow on the mountains. Mountain building, an internal process and part of the geosphere, generated the steep slopes along the glacier. Meltwater from the glacier that feeds into a river is part of the hydrosphere. Precipitation and melting of snow on the mountains generated a landslide that slid down the slopes onto the glacier. These are external processes. The glacier itself is also part of the hydrosphere, and its freezing and melting are external processes. During summer, wildfires are common occurrences in many parts of the western United States. Millions of acres are burned each year. The wildfire shown here occurred near Santa Clarita, California, in July 2004. Earth is a system in which various parts of its four major spheres interact in uncountable ways. Relate this idea to the situation pictured here. What atmospheric conditions might have preceded and thus set the stage for and/or contributed to this wildfire? What might have ignited the blaze? Suggest a natural possibility and a human possibility. Discuss how wildfires like the one shown here might influence future mass-wasting events in the area. Answer: a Atmospheric conditions would include low humidity and lack of rainfall or other precipitation. b A natural ignition source could be a lightning strike. A human possibility could be an improperly extinguished campfire. c Wildfires create a layer of loose ash debris while simultaneously destroying the vegetation. Vegetation is a stabilizing factor for soils and the soils will be loose when lacking vegetative cover. Water from firefighting efforts or from natural precipitation can mobilize this loose sediment and debris and cause mass-wasting events. Heavy rains in late July 2010 triggered the mass wasting that occurred in this mountain valley near Durango, Colorado. Heavy equipment is clearing away material that blocked railroad tracks and significantly narrowed the adjacent stream channel. What type of mass wasting likely occurred here? Explain your choice. Most of us are familiar with the phrase “One thing leads to another.” It certainly applies to the Earth system. Suppose the material from the Durango mass-wasting event had completely filled the stream. What other natural hazard might have developed? Answer: a This was likely a debris flow, specifically a mudflow. Debris flows occur when soil becomes saturated with water and it moves downhill as a large mass, frequently picking up other objects in its path. This picture clearly shows mud with some other large objects embedded. b Had the material filled the stream, local flooding could have occurred as the stream was blocked. DISCUSSION TOPICS What are some examples of weathering you might have seen locally? Answer: Examples of weathering I might have seen locally include the breakdown of rocks along coastal cliffs due to wave action (physical weathering) and the rusting of metal surfaces exposed to rain (chemical weathering). Which type of mass-wasting would scare you the most and why? Answer: The type of mass-wasting that would scare me the most is a landslide, due to its sudden and unpredictable nature, potentially causing significant damage and loss of life. Why does vegetation make such a good soil stabilizer? Answer: Vegetation makes a good soil stabilizer because its roots bind soil particles together, preventing erosion by water and wind, and enhancing soil structure and fertility. Why do you think people are so drawn to the shapes created by differential weathering? Answer: People are drawn to shapes created by differential weathering because they often form unique and striking geological formations, showcasing the intricate processes of erosion over time. What type of soil exists where you live? Why do you think this is true? Answer: The type of soil where I live is primarily loam, likely due to a mix of sand, silt, and clay particles, providing good drainage, fertility, and structure for gardening and agriculture. ADDITIONAL RESOURCES DVDs and Movies Earth Revealed, Episode 15: Weathering and Soils (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/series78.html Earth Revealed, Episode 16: Mass Wasting (1992) Annenberg Media, 30 minutes. Available on DVD or for free streaming video on demand from http://www.learner.org/resources/series78.html Japanese Landslide (2011) Oxford University Press Canada, 1 minute. Shows the downing of trees and powerlines in the area. Available at http://www.youtube.com/watch?v=r8QluRYLe9g Mudslide in Maierato, Calabria, Italy (2010) 1 minute. Shows a mudslide after heavy rains in Italy. Available at http://www.youtube.com/watch?v=-nx-gYYRu5I& Landslides 101, 4 minutes. National Geographic. Video of actual landslides with voiceover explanations of landslides. http://video.nationalgeographic.com/video/environment/environmentnatural-disasters/landslides-and-more/landslides/ Websites USGS gif animation of a San Francisco landslide, the processes responsible, and bedrock failure. http://elnino.usgs.gov/landslides-sfbay/images/SF_Fly.gif Case Study: Zhouqu, China landslide. An in-depth activity where students use their understanding of landslides coupled with the data provided to generate a brief written summary of the catastrophe. http://serc.carleton.edu/NAGTWorkshops/environmental/activities/64246.html Landslide from National Geographic. Short slide presentation showing the aftermath of various types of mass wasting events, coupled with text describing what a landslide is. http://education.nationalgeographic.com/education/encyclopedia/landslide/?ar_a=1 Image gallery of differential weathering features. http://www.pbase.com/dougsherman/weathering_ soils_and_erosion Solution Manual for Earth Science Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa 9780321928092, 9780321934437
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