This Document Contains Chapters 13 to 16 Chapter 13 The Solar System Contents Planets, Moons, and Other Bodies Mercury Venus Earth’s Moon Mars Jupiter Saturn Uranus and Neptune A Closer Look: Planets and Astrology Small Bodies of the Solar System Comets Asteroids Meteors and Meteorites Origin of the Solar System Stage A Stage B Stage C Overview You might use the technique of “zooming down” to the solar system as if aboard a galactic visitor's spaceship. By asking students what a galactic visitor would see upon approaching our solar system, you can discuss the relative dimension of the system, the counterclockwise movement of the planets around the Sun as viewed from the direction of the North Star, and the relative sizes of the planets. Depending on the time of year and the night viewing conditions at your location, students may be able to observe meteor showers at night. Usually the local paper carries information on potentially spectacular showers, and observation of these can be made as a homework assignment. Also, a trip to a planetarium (if within a reasonable distance) would be helpful. Most planetariums have one or more meteorites on display, and some have displays and exhibits of light phenomena, telescopes, and other related topics. Theories about the origin of the solar system are discussed in some detail, which leads naturally to the consideration of the planets as divided into two groups. The inner, or earthlike, planets are discussed as a group because of their similarities in terms of density, size, temperature, and chemical make-up. The outer planets are discussed as a group for the same reason. In turn, each planet is discussed individually. You will be able to supplement materials in this section as flyby missions and planetary probes provide more information. Suggestions 1. For students who persist in the ancient belief of astrology and the influence of the Sun, Moon, and planets, ask what is so special about the influence at time of birth, that is, the time when they moved through the birth canal. Even if a rational person believed that the position of the Sun, Moon, and planets could influence a person, it would seem more reasonable to assume that this influence would take place at the time of conception, about nine months earlier. 2. Have the students assist in collecting items that represent the Sun, the Moon, and various planets measured to scale. Use these objects to point out how measurements such as relative size and distance were first performed by the ancients. 3. If available, compare models of the geocentric theory of the solar system with that of the heliocentric theory. Show how epicycles helped answer questions about discrepancies noted in the early geocentric theory with its perfectly circular orbits. 4. Establish the relationship between a planet's distance from the Sun and its temperature, period of revolution, and orbital velocity. Consider other variables that may be related to planetary distance, such as rate of rotation, atmospheric composition, mass, and number of moons. 5. Models of the solar system are available from various scientific companies. Plastic balls of various sizes can be glued onto bases to make useful models. The balls representing the smaller planets can be mounted on pins; the other end of each pin can be secured into a wooden base. 6. To illustrate the effect of rotational rate on the shape of planets and stars, attach a centrifugal hoop to a hand rotator and vary the rate of rotation. For Class Discussions 1. The first and necessary event in the formation of the solar system was a. formation of an accretion disk. b. formation of protoplanets. c. initial flare-up of Sun, igniting fusion processes. d. supernovas of massive stars. 2. The motion of a planet as it moves around the Sun is a a. rotation. b. revolution. c. orbit. d. ellipse. 3. Which of the following planets does not belong with the other three? a. Mars b. Venus c. Earth d. Neptune 4. The planet with a very hot surface from a greenhouse effect is a. Mercury b. Venus c. Mars d. Uranus 5. The smallest planet is a. Mercury b. Venus c. Mars d. Jupiter 6. The largest planet is a. Jupiter b. Saturn c. Neptune d. Uranus 7. Leftovers from the formation of the early protoplanets might become a. asteroids. b. comets. c. meteors. d. meteorites. 8. The rings of Saturn are made up of a. dust and particles. b. clouds of frozen gases. c. thin layers of rocks. d. sheets of refractive liquids. 9. The planet with the longest day is a. Jupiter. b. Saturn. c. Venus. d. Earth. 10. Craters on the planets and moons of the solar system is the result of meteoroid bombardment that took place a. throughout the history of the solar system. b. about 4 billion years ago. c. 70 million years ago. d. some 6,000 years ago. Answers: 1d, 2b, 3d, 4b, 5a, 6a, 7b, 8a, 9c, 10b. Answers to Questions for Thought 1. The protoplanet nebular model is easiest to describe in stages: Stage A involves the creation of a large, slowly rotating cloud of dust and gases from the supernovas of earlier stars. These supernovas created the material of which the planets are made. In stage B the cloud begins to undergo gravity-induced collapse. The nebulous cloud begins to rotate faster as it contracts. Most of the mass is pulled into the center, forming the protostar that will become the Sun. The remaining gas and dust forms into an enormous accretion disk. The matter in the disk begins to clump together from numerous collisions. Stage C begins with the protosun becoming established as a star, perhaps undergoing an initial flare-up that may have blasted away most of the hydrogen and helium surrounding the inner planets. The planets underwent heating sometime early in their formation, allowing the heavier elements to be pulled to the center. Gases from the interiors of the planets gave them their early atmospheres. Comets were left over in the outer regions of the condensed cloud. Some people see different problems with this model. There are various parts of the model that may not seem credible, such as why did the planets form, why the accretion disk did not remain a disk, and why are the inner planets rocky when the outer planets are gaseous. 2. The terrestrial planets are mainly rock and iron, while the giant planets are primarily hydrogen and helium with some methane. In addition, some of the giant planets radiate away more energy than they receive from the Sun, which is not characteristic of the terrestrial planets. The protoplanet nebular model attempts to explain these differences by claiming that the inner planets lost most of their hydrogen and helium atmospheres in the flare-up during the ignition of the Sun. According to some astronomers, Jupiter is a “failed star.” It could have become a star, but it did not have enough mass to create the pressure and temperature necessary for the ignition of fusion in its core. 3. Mars has inactive volcanic regions, huge systems of canyons, terraced plateaus near the poles, and flat regions pitted with craters. The atmosphere is tenuous, and is about 95 percent carbon dioxide. The temperature is cold, about –53 degrees Celsius, and the water present is frozen in layered sheets. 4. The canyons and channels that appear to be riverbeds indicate that liquid water may have existed on Mars at one time. The atmosphere may have been denser, with the abundant carbon dioxide creating a greenhouse effect, causing the temperature to rise to the level where liquid water could exist. As carbonate rocks formed and volcanic activity abated, the planet lost its source of water vapor and carbon dioxide in the atmosphere, so the greenhouse effect declined. As the planet cooled, the water froze. 5. Jupiter and Saturn are less dense than Earth. Saturn is less dense than water, and if an ocean large enough could be found, the planet could float! These low densities indicate that the planets are made up mainly of light elements, such as hydrogen and helium. Measurements indicate that the planets both contain some heavier rocky substances. In both planets a thick layer of metallic hydrogen surrounds rocky cores. Above this layer is ordinary liquid hydrogen, and above this is the outer atmospheric layer of hydrogen, helium, water ice, ammonia gas, and ammonia clouds. The banded appearance of both planets, more noticeably Jupiter, is from a mixture of sulfur and organic compounds in the uppermost ammonia clouds. 6. Saturn’s rings are made up of particles of various sizes, ranging from minute dust particles to rocks and ices meters across. 7. Jupiter’s moon Io has the only volcanic activity known outside Earth and resembles a pizza in certain photographs. Europa is covered with smooth water ice networked with long, straight, dark ridges. Ganymede has the appearance of an active geologic history, and Callisto is the most heavily cratered object in the solar system. 8. The Sun and Jupiter are the two most massive bodies in the solar system, and both radiate more heat than they absorb. Jupiter, however, does not have the mass necessary to create the conditions required for the fusion reactions occurring in the Sun. 9. One of the theories attempting to explain why the Great Red Spot exists states that the spot is an upwelling of gas deflected from an island or some other surface feature below the atmosphere. The existence of a similar spot on Saturn would not really support or disprove this theory, because a similar structure could exist on Saturn as well. Since both planets are similar in make-up, the same types of storms could arise in both of their atmospheres. 10. Venus and Uranus exhibit retrograde rotation, opposite to the rotations experienced by the other planets. 11. Craters exist on most of the moons in the solar system as well as on the planets Mercury, Earth, and Mars. This indicates that earlier in the history of the solar system there were more rocks moving around. 12. Mercury is very unlikely to support life. The wide variations of temperature and the lack of an atmosphere make conditions too harsh for life to evolve. Venus, on the other hand, has too much atmosphere. The high pressures and temperatures on the surface, as well as the lack of water or free oxygen, make life as we know it improbable. Mars may have at one time supported life and is the most viable candidate for extraterrestrial life. This life will probably be microbial survivors from the earlier ages when Mars was warmer and had flowing water on its surface. The controversial findings of the Viking lander missions to Mars have not given much promise of finding life. The giant planets are very unlikely to have life evolve on them. Even if the planets do have surfaces, the pressures at the surfaces would be so great that anything present not made out of rock would be crushed. Speculation about life in the atmospheres of these planets has no evidence to support it. 13. A shooting star is a meteor burning in Earth’s atmosphere from atmospheric friction. Most meteors are small particles left by a comet in its orbit. The vast majority of meteors burn away before they can reach the surface of Earth; however, some do fall to the surface, and many museums have meteorites on display. 14. Asteroids are small rocky or iron bodies thought to be left over from a planet that never made it to the final stage before being pulled apart. The orbits of the asteroids mainly lie in a belt between Mars and Jupiter, leading to speculation that they are the remains of a planet that was somehow broken apart. Spectral composition studies, analyses of orbits, and studies of meteorites all indicate that the asteroids are not the remains of a planet. They are believed to have formed in the original solar nebula, but their close proximity to massive Jupiter prevented the clumping process that forms a planet. 15. Comets are estimated to originate some 30 AU to a light-year or more from the Sun. They are believed to be dirty ice balls left over from the formation of the solar system. For this reason they are studied for information about the early conditions of the solar system. 16. A meteor is an object falling into Earth’s atmosphere leaving behind a streak of smoke and light. Most meteors are probably rocks and boulders left over from the collision of asteroids, or they are small particles left by a comet in its orbit. 17. Meteorites are meteors that have made it to the surface of Earth. Most meteorites are the remnants of asteroid collisions. 18. A meteorite is defined as an object that has struck the surface of Earth, not the Moon. An object that strikes the Moon or any other planet is probably an asteroid, but more than 30 rocks from Mars and about 30 rocks from the Moon have been found on Earth. 19. The ice and frozen gases that are a part of the comet begin to vaporize as the comet approaches the Sun. These gases carry away small solid particles with them to form the tail of the comet. The dust and solid particles are visible because of reflected light from the Sun. Ultraviolet light from the Sun causes the gases to emit visible light, allowing the gases to be seen as well. For Further Analysis 1. Similarities – both the terrestrial and giant planets are believed to have rocky materials and iron as a core. Differences – the rocky materials of the giant planets are surrounded by tremendous amounts of hydrogen, helium, and methane. Speculations vary, but could include the idea that all planets at one time had hydrogen, helium, and methane atmospheres, but it was blown away from the terrestrial planets with the Sun startup. 2. 3. The mass, size, and density of Venus is very similar to Earth. Other than that, Venus is very hot, very high atmospheric pressure, and hostile to life. 4. Answers vary, but the probability of life as we know it on each of the other planets is near zero. 5. Answers will vary. 6. Comets are believed to be made of the original stuff of which the solar system formed, so studying a comet may provide insights about the formation of the solar system. Chapter 14 Earth in Space Contents Shape and Size of Earth A Closer Look: The Celestial Sphere Motions of Earth Revolution Rotation Precession Place and Time Identifying Place Measuring Time The Earth-Moon System Phases of the Moon Eclipses of the Sun and Moon Tides Overview This chapter considers the motions of Earth and Moon as an astronaut returning from some other planet might view them. It then considers how people on Earth and its Moon. This approach is intended to impress upon students the observation that Earth is just one of the nine planets of our solar system, which is located in one of billions of galaxies. The Foucault pendulum provides evidence of a rotating Earth and you can demonstrate the principle rather easily as a classroom demonstration. Tie a heavy object on the end of a string, and then start the object swinging back and forth in the directions of the students. Now slowly turn the direction you are facing and the students will be able to see that the swing of the pendulum remains in the same plane as the person holding the string moves. If you now swing the pendulum while standing over a spinning globe, students should be able to see that a person on the globe looking up would see what appears to be a pendulum that appears to turn once on its axis during a day. In the section covering seasons the definition and location of the tropic of Cancer, the tropic of Capricorn, the Arctic Circle, and the Antarctic Circle are discussed. Most students are aware that the Arctic Circle experiences long periods of darkness and long periods of daylight during a year’s time. You can use this knowledge to help explain why the Arctic Circle and the Antarctic Circle are located at certain latitudes. During the discussion of the precession of Earth you can point out that during the time of Jesus and for a considerable time before and after, sailors of the world had no North Star by which to navigate. Sailors during this period used either the Big Dipper or the Little Dipper as navigational guides. Most students will enjoy viewing some of the many beautiful color slides of the Moon that are commercially available. Since some will have telescopes or binoculars at their disposal point out that surface features of the Moon are also visible when it is not in its full phases. Suggestions 1. The principle by which the Foucault pendulum illustrates the rotation of Earth can be illustrated with a yo-yo or with a heavy mass attached to a string. Start the object swinging; then turn on your heels without touching the swinging object. Point out how the direction of the swinging object remains unchanged. A Foucault pendulum for use with a hand rotator is available from many commercial scientific suppliers. 2. A rotating stool and two masses of 2 kg each are ideal to illustrate concentration of mass and its effect on rotation. Ask a student of small stature to sit on the stool with arms extended. Place a 2-kg mass in each of the student’s hands, and then rotate the stool slowly. While rotating, have the student move the weight toward his or her chest. Observe the change in rate of rotation. 3. Earth photographed from the Moon appears to the eye to be a sphere. Have students make measurements of the polar diameter and the equatorial diameter of Jupiter to illustrate that the spin of a planet produces an oblate spheroid rather than a perfect sphere. 4. To illustrate procession of a rotating object in a gravitational field, use a toy top and spin it at various rates. 5. To illustrate a lunar and a solar eclipse, use two plastic balls of significantly different sizes. Darken the room and hold the two balls in the light from an overhead projector, slide projector, or filmstrip projector. Move one ball relative to the other to demonstrate both eclipses. 6. The seasons of Earth and the effect of its rotation can be well illustrated in a darkened room with a low-intensity light bulb (25-40 watt incandescent bulb mounted vertically) and a world globe. Maintain Earth’s 23.5˚ tilted axis away from the perpendicular as you rotate the globe, then move it in a slightly elliptical path about the light bulb. Point out the winter and summer seasons at both the North and South Poles as well as the Northern Hemisphere seasons at Earth’s perihelion and aphelion. 7. As a creative activity that requires understanding of the concepts presented in this chapter, students could write a creative essay about how life on Earth would be different if the axis were somehow shifted from its present inclined position to an upright position. For Class Discussions 1. Earth’s axis of rotation a. is parallel to the ecliptic. b. is perpendicular to the ecliptic. c. is inclined to the ecliptic. d. varies over the course of a year from perpendicular to parallel. 2. Earth’s seasons are a result of a. changes in orbital velocity during a yearly revolution around the Sun. b. variations in the Sun’s output and direction of output. c. the elliptical nature of Earth’s orbit around the Sun. d. the constant orientation of Earth’s axis of rotation. 3. In the Northern Hemisphere the Sun at noon reaches its lowest altitude above the horizon at the a. winter solstice. b. summer solstice. c. spring equinox. d. fall equinox. 4. The length of daylight and night are the same everywhere on Earth during a. a solstice. b. New Year day on a leap year. c. an equinox. d. no time since this does not happen. 5. Earth’s axis always has and always will point to the North Star, Polaris. a. Yes. b. No. 6. The most convincing evidence that Earth rotates comes from a. the fact that Earth has seasons. b. the observation that nighttime is always followed by daylight. c. watching a pendulum swing back and forth at different locations. d. measuring sunlight falling into a deep well. 7. You can identify where you are on Earth relative to the equator by using an identifying position based on a. the angle between the North Star and the ecliptic. b. the number of km from the Greenwich Observatory. c. Earth’s rotational axis. d. Earth’s position in its elliptical orbit around the Sun. 8. A sundial and a clock show the same time how many times a year? a. Once b. Twice c. Four times. d. All the time. 9. Leap years are needed to correct the calendar because a. Earth does not complete an exact number of turns during one complete revolution. b. Earth completes a slightly greater number of turns during one complete revolution. c. Earth turns faster around the equator than it does at the poles. d. Earth is slowly spinning down. 10. A solar eclipse can only occur with a a. full moon. b. new moon. c. quarter moon. d. any moon phase. Answers: 1c, 2d, 3a, 4c, 5b, 6c, 7c, 8c, 9a, 10b. Answers to Questions for Thought 1. (a) The variation in the number of daylight hours is caused by the tilt of Earth’s axis relative to the plane of the ecliptic. When the North Pole is pointed toward the Sun, the Sun is hitting more of the Northern Hemisphere than the Southern Hemisphere. Conversely when the South Pole is pointed in the direction of the Sun, the Southern Hemisphere receives more sunlight. (b) The variation in the seasons is related to this variation in daylight hours because it is also caused by the axial tilt. When the North Pole is pointed toward the Sun, the Sun strikes the surface of the Northern Hemisphere more directly. This light has traveled through less atmosphere to reach the surface, so less has been absorbed. In winter, when the north polar axis is pointing away from the Sun, the light strikes Earth at a glancing angle because it has to travel though more air to reach the surface. 2. On the equator, an almost nonexistent shadow would be observed at noon on the day of the autumnal equinox. (a) In the Northern Hemisphere shadows point northward at noon on the day of the autumnal equinox. (b) A southward-pointing shadow would be seen in the Southern Hemisphere at noon on the day of the autumnal equinox. 3. “Solstice” means, “Sun stands still” in Latin. The solstices occur when the Sun has the highest altitude in the sky of either the Northern or Southern Hemisphere. This occurs when the axis of Earth is pointing as close to the Sun as possible, or when the Sun is as far north or south as it will travel on the celestial sphere. The solstices occur on about June 22 and December 22. 4. “Equinox” is from the Latin meaning “equal nights.” On the equinoxes, both day and night are of the same length. On the equinox, the Sun crosses the celestial equator when viewed on the celestial sphere. The approximate dates for the equinoxes are March 21 and September 23. 5. Earth’s axis is used to define the north-south position or latitude of a point on the surface. The North Pole is defined as +90° latitude, while the equator is 0° latitude and the South Pole is –90°. North south lines run through the poles to identify how far east or west an object is to a reference line. These lines are referred to as meridians of longitude. 6. Answers will vary. 7. The tropic of Cancer and the tropic of Capricorn identify the limits toward the poles where the Sun appears directly overhead during the year. They are located at 23.5° N and 23.5° S latitude respectively. The Arctic and Antarctic circles identify the limits toward the equator where the Sun appears on the horizon all day for at least once during the summer. They are located at 66.5° N and 66.5° S latitude respectively. 8. (a) The movement of the Sun across the celestial meridian is noon. (b) A.M. stands for ante meridiem, or the time before the Sun crosses the celestial meridian. (c) P.M. stands for post meridiem, or the time after the Sun has crossed the celestial meridian. 9. Standard time zones were established to avoid the confusion of having clocks set to local mean solar time. Each time zone is 15° wide in terms of longitude. This was chosen so that there are twenty-four time zones, one for each hour in the day. In this way, the variation in clock time between the time zones is in units of whole hours. 10. Texas is in the Central Time zone. (a) The Eastern Time zone, where Jacksonville, Florida, is located, is one hour later than in the Central Time zone, so 12:00 noon in Texas is 1:00 P.M. in Jacksonville. (b) Bakersfield, California is located in the Pacific Time zone, where it is two hours earlier than in the Central Time zone. At 12:00 noon in Texas, it is 10:00 A.M. in Bakersfield. (c) At the North Pole, the time is defined to be Greenwich Mean Time, or 7:00 P.M. when it is 12:00 noon in Texas. 11. Since the orbit of the Moon is inclined to Earth’s orbit, the Moon is usually above or below the shadow of Earth when it passes behind. 12. During a new moon, the Moon is located between Earth and the Sun (but not usually directly between). First quarter is when the Moon has passed new moon and is still on the Sun side of Earth. A half-moon occurs when the Moon has moved beside Earth, while three-quarters is when the Moon begins to move behind Earth. A full moon is when the Moon is farthest from the Sun, and behind Earth. The phases go in reverse order after the full moon to reach another new moon. 13. A “new earth” or dark disc would be observed from a full moon. 14. The Moon would be full because if it were in an earlier phase it would rise earlier, while a later phase would rise later. Only when the Moon is on the opposite side of Earth from the Sun will it rise as the Sun sets. 15. The tilt of the orbit of the Moon relative to Earth’s orbit causes the shadow of the Moon usually to fall above or below. 16. An eclipse of the Sun can only occur during a new moon. During other phases, the Moon is not positioned between Earth and the Sun. 17. (a) Spring tides occur during full and new moons. The alignment of the Sun, Moon, and Earth allows the gravitational effects of the Sun and Moon to combine to make larger tides. (b) Neap tides occur during the half phases when the Sun and Moon are at right angles when measured from Earth. 18. The Moon’s gravity pulls Earth away from the ocean on the opposite side. This forms a tidal bulge on the outside of Earth’s path of revolution on the opposite side from the Moon. The bulge on the same side as the Moon is caused by the Moon’s gravity pulling the water toward the Moon. For Further Analysis 1. Similarities – both are the beginnings of seasons recognized from the altitude of the Sun in the sky at noon. Differences – an equinox marks the beginning of summer or winter and occurs when the Sun reaches its highest or lowest altitude in the sky at noon; a solstice marks the beginning of spring or fall and occurs when the sun is situations so daylight and night are of equal length. 2. Earth is closest to the Sun in January. The orientation of Earth’s axis to incoming sunlight is more important than distance in determining seasons. 3. The plane of the Moon’s orbit is inclined to Earth’s orbit about 5° so the shadow from the Moon or the shadow from Earth usually falls above or below the other body, too high or too low to make an eclipse. 4. The difference is a result of the shape of Earth’s orbit, and the fact that the angles between the plane of the ecliptic and the plane of the equator are different. 5. Answers will vary, but the reason is as follows: The period of twelve hours and twenty-five minutes is half the average time interval required for the Moon the pass directly overhead, and the tidal bulge follows the Moon. The daily rotation of Earth on its axis is 24 hours, which is different from the time required for the Moon to pass directly overhead.\ Chapter 15 The Earth Contents Earth Materials Minerals A Closer Look: Asbestos Rocks Igneous Rocks Sedimentary Rocks Metamorphic Rocks The Rock Cycle The Earth’s Interior The Crust The Mantle Earth’s Core A More Detailed Structure Plate Tectonics Evidence from Earth’s Magnetic Field Evidence from the Ocean A Closer Look: Seismic Tomography Lithosphere Plates and Boundaries A Closer Look: Measuring Plate Movement Present-day Understandings Overview This chapter is an introduction to the dynamic, ever-changing Earth and how geology seeks to understand the natural processes behind these changes. It begins with an account of the materials that make up Earth, including the chemical composition of various Earth materials and the overall structure of Earth. The solid Earth materials include minerals and rocks. A mineral occurs naturally, it is inorganic in composition, and it has a definite internal structure. The composition of a mineral can vary only between well-defined limits, a feature that accounts for the thousands that geologists have identified. Most minerals are composed of oxygen, silicon, aluminum, and either sodium or potassium. Most of the other elements appear in such small quantities as to be considered impurities. If iron-bearing minerals did not concentrate while in the molten state, iron, along with metals in other ore minerals, could not be mined profitably. Minerals are classified and identified according to various properties, the most useful of which are streak, hardness, and cleavage. These properties can be determined readily by geologists at a deposition site. Sedimentary rocks may include organic matter along with naturally occurring minerals. This category of rock is the product of erosional processes. The study of sedimentary rocks has made scientists aware of changes in living organisms and conditions on Earth when the sediment was laid down. Further correlation of fossil life and layers of sediment, as well as the geologic processes that occur at mid-ocean ridges, have left little doubt that our continents have drifted apart from the gigantic landmass they formed at least twice in the past. Metamorphic rocks are formed from sedimentary, igneous, or other metamorphic rocks. Most metamorphic rocks were typically formed as a result of exposure to great pressure and high temperatures. They did not re-melt under these conditions, however. Other metamorphic rocks were formed as hot fluids circulated through them. The structure of Earth is considered from two viewpoints (1) considering Earth to have the three main parts of a crust, mantle, and a core, and (2) considering Earth to have a lithosphere (rocky layer), asthenosphere (weak, plastic layer), mantle, outer core, and inner core. Both structural considerations are adequate models, with the second proving more detail that the three-part model. The concept of plate tectonics is introduced after a discussion of the asthenosphere and sea-floor spreading. As a model, plate tectonics explains volcanic activity, earthquakes, and the diversity of features of relief found on the surface of Earth. Suggestions 1. Specimens can be placed in a display cabinet for students to view. See that each specimen is labeled in terms that the nonscience students can readily understand. 2. A set of color slides can be used to show rock types, formations, and illustrations of the geologic processes that shape the surface of Earth. Choose selections from the many available from supply houses that are most beneficial for the presentation of this and other geology-oriented chapters. Supply houses can also supplement the types of rocks and features that are not present in your location. 3. The petrology collection of rocks and minerals available from supply houses is an excellent way to teach geology concepts for smaller classes. Many specimens from these collections have features that can be distinguished by students in larger classes. A video camcorder is useful to display close-ups of specimens on the screen for all students to view. 4. Cut out the various landmasses from a world map and try to assemble them so the masses fit together as pieces of a jigsaw puzzle. Explain how erosion and other geologic processes might account for areas from which landmasses are missing. Also point out to the students that the best fit between continents is not between shorelines but between continental shelves. 5. The model of Earth's interior has changed since the early 1960s. Students could investigate how the model has changed by reviewing journal articles before and after that time. 6. If Los Angeles, California, is on a plate moving at a rate of 10 cm per year, calculate how long it would take for Los Angeles to move the distance to where San Francisco, California, is presently located. For Class Discussions 1. One of these minerals does not belong with the other three. a. quartz b. gypsum c. mica d. orthoclase 2. One of these rocks does not belong with the other three. a. gypsum b. limestone c. schist d. sandstone 3. One of these rocks does not belong with the other three. a. granite b. marble c. basalt d. rhyolite 4. The rock cycle concept states that all rocks a. are endlessly changing from one type to another. b. will eventually be sedimentary rocks. c. will eventually be metamorphic rocks. d. will eventually be igneous rocks. 5. Volcanoes are least likely to be as frequent on which type of plate convergence? a. ocean-continent b. ocean-ocean c. continent-continent d. all are the same 6. A deep oceanic trench is most likely to be associated with which type of plate boundary? a. divergent b. convergent c. transform d. any of the above 7. Evidence that Earth has a liquid outer core and a solid inner core comes from a. drilling samples. b. volcanoes. c. earthquakes. d. laboratory simulations. 8. About how far would a plate, such as the North American plate, be expected to move in a century? About a. 1 m b. 3 m c. 10 m d. 25 m 9. Convincing evidence for the support of the plate tectonics theory came from studies of a. paleomagnetics. b. meteorites. c. earthquakes. d. shapes of continents. Answers: 1b, 2c, 3b, 4a, 5c, 6b, 7c, 8b, 9a. Answers to Questions for Thought 1. A rock is an aggregation of one or more minerals and perhaps mineral materials that have been brought together into a cohesive solid. 2. The rock cycle is a concept that an igneous, sedimentary, or metamorphic rock is a temporary stage in the ongoing transformation of rocks to new types. 3. Igneous rocks formed as hot, molten magma cooled and crystallized to firm, hard rocks. Slowly cooling magma forms coarse-grained intrusive igneous rocks, and quickly cooled magma produces fine-grained extrusive igneous rocks. Sedimentary rocks are formed from sediments. Conglomerate rocks are made up of large sediments, sandstone contains intermediate-sized sediments, and shale is made up of fine sediments. These rocks are formed through compaction and cementation of the sediments. Metamorphic rocks are previously existing rocks that have been changed by heat, pressure, or hot solution into a different kind of rock without melting. Sedimentary rock can be changed from shale to slate and then to schist, and finally gneiss. Each stage has a characteristic crystal size and alignment known as foliation. 4. On the surface sedimentary rock would be the most expected, because the forces of erosion are continually working to provide new source material for this type of rock. Deeper into the crust, metamorphic rock would prevail in the higher pressures and temperatures. Even deeper and on the ocean floors, igneous rock would be found in quantity, close to the hot magma from which it forms. 5. Basalt is dark and fine-grained, whereas granite is light-colored and coarse-grained. Basalt makes up much of the ocean basins. Seafloor spreading allows the hot magma to contact the seawater and cool rapidly to form basalts. Granite is common on the continents because the air is not able to cool magma as quickly. 6. If a rock has basalt’s chemical composition but it is not fine-grained, it is gabbro and not basalt. 7. As sediments are deposited, the overlying sediments cause an increasing pressure on the sediments below. This process squeezes the grains together, reducing the pore spaces. This compaction of the grains reduces the thickness of the sediment deposit and squeezes out the water. Cementation by chemical deposits between the sediment particles binds the particles together into a rigid, cohesive mass of sedimentary rock. 8. Metamorphic rocks are previously existing rocks that have been changed by heat, pressure, or hot solutions into a distinctly different kind of rock. The temperatures involved must be less than the melting point of the rock, because if the rock melts and re-solidifies, it is an igneous rock and not a metamorphic rock. 9. Information about the core is obtained from seismological data, or earthquake waves that pass through the core; the nature of meteorites, which give information as to the relative abundance of materials in the nebula that condensed to form the planet; and geological data at the surface of the Earth. 10. The asthenosphere is the layer of plastic, mobile, yielding rock located from 130 km to 160 km in depth. The asthenosphere is believed to be one of the important sources of magma that reaches Earth's surface. 11. The magnetic bands are a result of the “flipping” of the magnetic field of Earth several times in the last 150 million years. When the iron minerals in the forming basalt are exposed to this field, they become magnetized and freeze in a record of the field direction as they solidify. 12. The seafloor is new crust that is created in the ridges. Older seafloor is plowed under at the edges of continents in subduction zones to re-melt and possibly migrate back to the spreading ridge. Therefore, all the old rock has already been pushed into a subduction zone in this recycling process. 13. Divergent boundaries occur between two plates moving away from each other. New crust is formed at these boundaries. Convergent boundaries occur between two plates moving toward one another. This is where crust is destroyed to make room for the newly created crust at the divergent boundaries. Transform boundaries occur between plates sliding by each other. Crust is not created or destroyed in these regions; however, many earthquakes are caused by sudden jerks at these boundaries. 14. According to plate tectonics the lithosphere is broken up into a number of fairly rigid plates that move on the asthenosphere. Some plates contain continents and part of an ocean basin and others contain only ocean basins. The motion of the plates and the interaction at the boundaries explain a number of geographic features. Volcanoes are explained by the subduction of one plate below another, mountain ranges are formed by plates colliding or sliding past each other, and new crust is created in suboceanic divergence boundaries. 15. An oceanic trench is a region of great depth that marks a subduction zone of an ocean-continent plate convergence. The trench is formed as the ocean plate is forced beneath the continental plate. 16. The most probable source of earthquakes in southern California is the San Andreas Fault, which is a transform boundary between the Pacific Plate and the North American Plate. If the plates stick together for a time, then violently break apart, an earthquake occurs. 17. This part of the North American Plate is near the plate boundary. This boundary is probably an ocean-continent plate convergence. A deep trench would probably be caused off the coast on the seafloor by the subduction of the oceanic plate. 18. The crust is being created at the mid-oceanic ridges as plates spread apart and new crust forms from the upwelling mantle. This crust replaces that which is forced down into the interior of Earth at subduction zones. The material forced into the subduction zones may cause volcanoes, creating new continental crust, or it may be recycled back to the spreading center to form new crust. For Further Analysis 1. Answers will vary, but ice seems to fit the definition of a mineral. 2. Similarities – all rocks are made up of one or more minerals and perhaps other materials. Differences – igneous rocks formed as a hot, molten mass of rock materials cooled and solidified; sedimentary rocks formed from particles or dissolved materials from previously existing rocks; metamorphic rocks formed from igneous or sedimentary rocks that were deformed or recrystallized by high temperatures and pressures. 3. Volcanoes form where plate boundary convergence is taking place. The eastern United States and Canada are near the center of the North American Place, not a boundary, so you would not expect volcanoes to occur there. 4. Atmospheric gases and vapors, water of the surface, and flowing interior rock materials all cycle. Other planets lack the atmospheric gasses, liquid water, or internal molten rock materials necessary for cycling. 5. Weathering and erosion produce sedimentary rocks, and this is what is occurring on Earth’s surface. 6. Answers will vary. 7. Answers will vary, but should include evidence of an interior with molten or plastic-like materials. Chapter 16 The Earth’s Surface Contents Interpreting Earth’s Surface Processes That Build Up the Surface Stress and Strain Folding Faulting Earthquakes Origin of Mountains A Closer Look: Volcanoes Change the World Processes that Tear Down the Surface Weathering Erosion Mass Movement Running Water Glaciers Wind Overview This chapter is about the dynamic, ever-changing Earth and how geology seeks to understand the natural processes behind these changes. First, processes that build up land are considered such as folding, faulting, and other responses to the stresses created by the movement of Earth's plates. Plate tectonics has changed the accepted way of thinking about the solid, stationary nature of Earth's surface and ideas about the permanence of the surface as well. The surface of Earth is no longer viewed as having a permanent nature, but is understood to be involved in an ongoing cycle of destruction and renewal. Old crust is destroyed as it is plowed back into the mantle through subduction, melts, and becomes mixed with the mantle. New crust is created as molten materials move from the mantle through sea-floor spreading and volcanoes. Over time, much of the crust must cycle into and out of the mantle. Elevated landscape features are exposed to the elements and undergo weathering and erosion processes that have sculptured them into today's landscapes. The sculpturing, cutting, and transportation actions of running water, wind erosion, and glacial effects are covered after first considering the preparation of the surface through physical and chemical weathering. There are many examples of the results of chemical and mechanical weathering that can be observed by students during their travels. Many road cuts from the building of highways afford opportunities for students to observe how the relatively smooth faces of these road cuts are slowly disintegrating, with the resulting buildup of talus deposits at the bottom. Sculpturing of Earth’s surface takes place so gradually that humans are usually not aware that it is happening. Some events such as a landslide or the movement of a big part of the beach by a storm are noticed. Both the continual, slow downhill drift of all the soil on a slope and the constant shift of grains of sand along a beach are outside the awareness of most people. People do notice the muddy water moving rapidly downstream in the swollen river after a storm. Few, however, are conscious of the slow, steady solution of limestone by acid rain percolating through it. Yet, it is the processes of slow movement, shifting grains and bits of rocks, and slow dissolving that will wear down the mountains, removing all the features of the landscape that you can see. This rate of removal is continual and slow, and would require about 20 million years or so to level the continents to sea level. However, the destructive forces have never won in the past. The constructive forces of diastrophism and vulcanism seem to balance the continual and slow degradation. The look of the landscape has changed and the shapes and sizes of continents have changed. You would expect such changes as the forces of upheaval build up the land and the forces of degradation tear it down. So far, the records indicate that the forces must be balanced since the continents have persisted about the same average elevation above sea level for billions of years. Suggestions 1. Physiographic relief globes that provide a view of Earth's interior (crust, mantle, and core) and plastic relief globes with a raised relief are available from scientific supply companies. 2. A set of color slides can be used to show rock types, formations, and illustrations of the geologic processes that shape Earth's surface. Choose selections from the many available from supply houses that are most beneficial for the presentation of this and other geology-oriented chapters and that supplement the types of rocks and features that are not present in your location. 3. Models of rock layers are available from supply houses. These models are helpful in illustrating several of the concepts discussed. A deck of cards spread out on a desk can be used to illustrate the relative age of rock layers. Cards toward the bottom of the deck must have been laid down before the upper ones if the deck has not been disturbed. 4. If a road cut is nearby, ask students to figure out the local Earth history by studying the road cut. 5. Ask the students to list the types of weathering and agents of erosion according to their order of importance in the immediate geographic region. Does the order vary from their respective home areas? 6. A stream table is extremely useful to illustrate the erosive features produced by running water. The device uses a mixture of sand of various colors or of sand and several different soils. The stream table should be set in operation and placed on display to permit students to observe changing conditions over time. 7. To illustrate physical weathering, a handful of sharp-edged pieces of limestone can be placed in a jar with a lid and shaken several hundred times. Changes in the sharpness of the rock edges and changes in the composition of the water will show the effects. To illustrate chemical weathering, compare what happens to a sample of limestone in a beaker of water to one in a beaker of water with dilute hydrochloric acid. The chemical action releases bubbles of carbon dioxide. 8. Assign students the task of finding and reporting on six different examples of weathering and any examples of erosion they can find on or near the campus. For Class Discussions 1. The volcanoes along the Washington and Oregon coastline originated from a. ocean-continent convergence. b. ocean-ocean convergence. c. a divergent boundary. d. a transform boundary. 2. The Appalachian Mountains were a result of erosion after an origin of a. folding. b. faulting. c. volcanic. 3. The Sierra Nevadas of California were formed by a. folding. b. faulting. c. volcanic activity. 4. One of the following formed as fault block mountains: a. Black Hills of South Dakota. b. Adirondack Mountains of New York. c. Teton Mountains of Wyoming. d. Mauna Loa in Hawaii. 5. One of the following was formed by volcanic activity: a. Black Hills of South Dakota. b. Adirodack Mountains of New York. c. Teton Mountains of Wyoming. d. Mauna Loa in Hawaii. 6. Each higher number on the Richter scale means how much more ground movement than the preceding number? a. 2 times more. b. 5 times more. c. 7 times more. d. 10 times more. 7. Which of the following is the most important agent of erosion? a. glaciers b. wind c. ocean waves d. streams 8. Which one of the following does not belong with the other three? a. floodplain b. U-shaped valley c. delta d. meanders 9. Glaciation might leave a deposit called a a. moraine. b. delta. c. dune. d. oxbow. 10. A slowly flowing stream with wide meanders in a wide floodplain is in what stage? a. youth b. maturity c. old age d. rejuvenation 11. Is it possible to have erosion without weathering? a. Yes. b. No. Answers: 1a, 2a, 3b, 4c, 5d, 6d, 7d, 8b, 9a, 10c, 11b Answers to Questions for Thought 1. The principle of uniformity is the frame of reference that the same geologic processes that change rocks seen today are the same processes that changed them in the past. It is based on the assumption that Earth’s history can be interpreted by tracing it backward from the present to the past. This tracing requires a frame of reference of slow, uniform change. 2. (a) A slow increase of pressure on deeply buried warm layers of rock would create an elastic deformation and then an elastic flow. (b) A slow increase of pressure in cold rock layers would result in a plastic deformation. (c) A quick increase in pressure on cold rock or warm rock would result in a break. 3. An anticline is an arch-shaped fold in rock layers, while a syncline is a trough-shaped fold. 4. The presence of folded sedimentary rock indicates that the region has undergone geologic stress in the time since the sedimentary rock was formed. 5. Faulting is generally caused by sudden stress on the cooler, more brittle rock near the surface. A fault is directly caused by movement between the rocks on either side of a fracture. Folding occurs in deeper rock, which has stress applied more slowly. 6. Normal faulting results from pulling apart stresses such as those associated with diverging plates. Reverse faulting results from compressional stresses that may be from converging plates. 7. The sudden movement of blocks of rock produces vibrations that move out as waves throughout Earth. These vibrations are known as earthquakes. Generally, the motion at plate boundaries creates the stress conditions necessary for the sudden movements of the blocks of rock. 8. The theory of plate tectonics would predict that earthquakes would occur at any plate boundary, since stresses on rock always occur in these regions. 9. The time lag between the S-waves and P-waves gives the distance to the earthquake source. The direction to the source is calculated by drawing a circle on a map using the calculated distance as the radius. The point where the circles of three recording stations cross identifies the earthquake source. 10. Quartz sand, clay minerals, metal oxides, and soluble salts are the end products of granite weathering. The clay minerals, and soluble salts are washed away in the weathering process. The quartz sand and metal oxides are generally removed through erosion. 11. Rainfall carries the products of weathering to a stream through sheet erosion as well as carrying the soluble products of weathering. The small stream moves to larger channels and transports the materials as dissolved rock minerals carried in solutions, as clay minerals and small grains carried in suspension, and as sand and larger rock fragments that are rolled, bounced, and slid along the streambed. 12. A floodplain is the wide, level floor of a valley built by a stream. It gets its name because this is where the stream floods when it spills out of its channel. 13. Youth is characterized by a steep gradient, a V-shaped valley without a floodplain, and the presence of features that interrupt its smooth flow such as boulders in the streambed, rapids, and waterfalls. Erosion eventually brings the onset of the mature stage. The boulders, rapids, and waterfalls are eroded away, the valley smoothed, and the gradient reduced. Meanders begin to form over the wide floodplain, and the higher elevations are now sloping hills rather than steep channel sides. Old age is marked by a very low gradient in extremely broad, gently sloping valleys. The meanders have become broad sweeps across the wide floodplain. The flow is sluggish, and floods are more common. 14. Abrasion from the erosion process of glaciers pulverizes rock into ever-finer fragments, eventually producing a powdery, silt-sized sediment called rock flour. 15. If the stream had an outlet lower than sea level, such as the Dead Sea, the erosion could continue as far down as the stream could flow. Otherwise, at sea level, if the stream lets out into the sea, the flow rate would be very slow and very little erosion would occur. 16. Glacial erosion occurs both by pulling rocks up and along with the glacier as well as by abrasion. There is very little erosion above the glacier, however, causing the valley to be U-shaped. A stream fed by rainfall allows the land above it to be eroded rapidly because it provides an outlet for the rainwater to carry away its sediments. In addition, the stream erosion occurs much faster than that of a glacier, cutting deeply into the land, creating a V-shaped valley. 17. Stream erosion: A stream develops a valley on a widening floodplain. The development of a steam channel into a widening floodplain seems to follow a general, idealized aging pattern. When the stream is on a recently uplifted land mass, it has a steep gradient, a V-shaped valley without a floodplain, and the presence of features that interrupt its smooth flow such as boulders in the streambed, rapids, and waterfalls. During maturity meanders form over a wide floodplain that now occupies the valley floor. During old age the stream has a very low gradient in extremely broad, gently sloping valleys. The stream now flows slowly in broad meanders over the wide floodplain. Floods are more common in old age since the stream is carrying a full load of sediments and flows sluggishly. Wind erosion: Two major processes of wind erosion are called abrasion, and deflation. Wind abrasion is a natural sand-blasting process that occurs when the particles carried along by the wind break off small particles and polish what they strike. Deflation, named after the Latin meaning, “to blow away,” is the widespread picking up of loose materials from the surface. Deflation is naturally most active where winds are unobstructed and the materials are exposed and not protected by vegetation. Glacial erosion: Deposits of bulldozed rocks and other materials that remain after the ice melts are called moraines. Plucking occurs as water seeps into cracked rocks and freezes, becoming a part of the solid glacial mass. As the glacier moves on, it pulls the fractured rock apart and plucks away chunks of it. The process is accelerated by the frost wedging action of the freezing water. Plucking at the upper-most level of an alpine glacier, combined with weathering of the surrounding rocks, produces a rounded or bowl-like depression known as a cirque. 18. Stream deposits: When a stream flows into the ocean or a lake it loses all of its sediment-carrying ability. It drops the sediments, forming a deposit at the mouth called a delta. Wind deposits: The most common wind-blown deposits are dunes and loess. A dune is a low mound or ridge of sand or other sediments. Glacier deposits: Glaciers produce a wide variety of materials from rocks, soil, and sediments by the leading edge of an advancing glacier. Deposits of bulldozed rocks and other materials that remain after the ice melts are called moraines. The pulverizing of rock into ever-finer fragments eventually produces powdery, silt-sized sediment called rock flour. 19. Chemical weathering occurs more in a humid climate where sufficient moisture is available. Not as much chemical weathering occurs in a dry climate because water is necessary in the scheme of things. 20. Answers will vary but could include local effects—as the rain forest is cleared away and burned for new fields of tropical agriculture, the thin humus layer is soon exhausted and subjected to leaching without replenishment. The remaining laterite is incapable of sustaining agricultural efforts, sometimes baking into a hard, brick-like layer that is impossible to plow. Other reasons include the destruction of oxygen-producing vegetation, the worldwide increase in carbon dioxide levels, and the destruction of the plant gene pool. For Further Analysis 1. Answers will vary, but should include evidence of observable geologic events and an understanding of geologic time. 2. Answers will vary, but should describe geologic events associated with plate tectonics, and evidence from geologic history about the past. 3. Similarities – both elastic and plastic deformation are changes brought about by the application of forces. Differences – elastic deformation is temporary and the material returns to its original shape; plastic deformation permanently alters the shape of a material. 4. Variables: A ductile condition from confining pressure and deep burial; relatively slow application of compressive stress. 5. More earthquakes occur along a fault plane near the earth’s surface because rocks near the surface are more brittle than ductile, and relative movement takes place along the fault. 6. Similarities – both are changes in the destruction of solid rock. Differences – weathering is the slow breaking up, crumbling and destruction of solid rock; erosion is the physical removal of weathered rock materials. 7. Answers will vary. 8. No, sea level is the limit of erosion. Observation of a delta will show that materials are deposited, not eroded at sea level. Instructor Manual for Integrated Science Bill W. Tillery, Eldon D. Enger , Frederick C. Ross 9780073512259
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