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Question Answers
I-1. Sediments are carried to the sea by water, and as they settle out on the sea bottom, they distribute over a wide area, forming a flat and mostly horizontal layer.
I-2. a) Your answer could include any of the following: tidelands, deltas, large lakes, or shallow seas. b) in young active mountain ranges, such as the Alps or Himalayas. c) almost anywhere above in a desert or on a beach. e) almost anywhere above sea level.
I-3. Both a) and b) have been observed to occur in recent years, and so are uniformitarian. The rate of erosion in the Grand Canyon is sufficient today to have carved out the canyon in a million years or so, and therefore d) is also uniformitarian. While floods are frequent occurrences, no worldwide flood has been observed in recent times, and so e), is catastrophist. An asteroidal collision has not been observed to happen on Earth or on other planets, though it probably did happen in the past. It, too, would be classed as catastrophist. The distinction between catastrophist and uniformitarian models is not always clear, because it depends on the definition of "recent times."
I-4. According to the Principle of Superposition, the topmost layers are youngest. Therefore, the trilobites came first, and the dinosaurs appeared later.
I-5. For the Principle of Original Horizontality, your answer might include something like: the thin layer of mud left at the bottom of a dried up puddle, mud and gravel washed out over a road after a storm, the mud and gravel left after a flood, or any other example of sediment spread out and deposited in a flat sheet by water or wind. For the Principle of Superposition, it is the sequence of deposition that is important. The mud on top of the road was deposited after the road was built. Mud and gravel covering grass came after the grass grew. In a pile of magazines in your living room or den, the oldest magazines are on the bottom of the pile, provided that no one has come along and reshuffled them.
I-6. Each time a parent atom decays, it is replaced with one atom of the daughter. Hence the total number stays the same.
I-7. a) There were zero Lead-207 atoms present when the zircon formed, since zircon excludes lead at the time of formation. b) There were 400 billion Uranium-235 atoms present at that time, since each Lead-207 atom present today formed by changing from a Uranium-235 atom. c) The parent Uranium-235 is down to 25% of its original number, hence the zircon is two half-lives old, or 1.4 billion years.
I-8. Since Carbon-14 is the parent, you can read off the number of half-lives directly from Figure 1.5. Locate 30% on the vertical axis and draw a horizontal line from it to the curve, then straight down to the horizontal axis. You should come up with something like 1-3/4 half-lives. Since one half-life for Carbon-14 is 5,730 years, the age of the wood is 1.75 times 5,730, or about 10,000 years.
I-9. Ordovician, Carboniferous, Triassic, Jurassic, Tertiary.
I-10. From top to bottom: Tertiary, Jurassic, Triassic, Carboniferous, Ordovician.
3-1. The principal difference was in the assembly <of all the continents into one supercontinent in the Late Carboniferous.
3-2. According to Wegener's theory, Africa, South America, and Antarctica were still attached to one another when Mesosaur lived. Its original habitat split apart when the southern continents broke up.
3-3. Your answer should include mention of thin, rigid plates that are moving about the surface of the Earth.
3-4. Lines or bands of earthquakes are the most reliable evidence for a plate boundary. You should realize, though, that not all earthquakes occur on plate boundaries. Compare Figure 3-2 to Figure 3-3.
3-5. Wegener's theory relied only on motion of the continents. In his theory, the ocean floor did not move. In plate tectonics it is the plates that <move, and they may carry continent, ocean floor, or both.
3-6. Either temperature or rigidity would be correct answers, since the asthenosphere is softer (less-rigid) than the lithosphere, because it is hotter and very close to its melting point.
3-7. Either rock type or density would be satisfactory answers, though you should recognize that mantle rocks are much denser than crustal rocks.
3-8. Lithosphere and asthenosphere refer to physical properties (temperature and rigidity) which can be different in different parts of the mantle.
3-9. If every part of Mt. Everest were in perfect isostatic equilibrium with its root, the tip of that root would extend 4.5 times its height below the average crustal thickness, or 39,600 m (39.6 km). This is in addition to the normal continental crustal thickness of about 30 km (see Figure 3-4).
3-10. Since new oceanic crust is created at the ridge crest and is then carried away by sea-floor spreading, youngest ocean floor should be found near the ridge and oldest ocean floor far from the ridge.
3-11. The magma produced by the subduction zone rises from a depth of approximately 100 kilometers below the surface. This zone is located east of the trench (the subducting slab dips downward towards the west). This slab is the edge of the Nazi Plate which is diving under the edge of South America, west to east. The factor which determines which plate subducts beneath the other is density. The Nazca plate is denser than the South America plate. Where they converge the denser plate sinks beneath the less dense plate (See Figure 3-7 and 3-11).
3-12. The elevation or depth of portions of the earth’s surface is determined by the density of the tectonic plate, with two slightly complex instances. In the first instance, the oceanic trench, the plate is actually being pulled by the subducting slab, to a lower elevation. This forms the unusually great depth of oceanic trenches. The second instance is also associated with subduction zones. Here either the addition of lower density rocks and a resulting increase in the thickness of a tectonic plate (associated with granitic composition plutons), or even larger increases in the thickness of continental crust (such as where the continental Indian plate is subducting horizontally beneath the Eurasian plate), to a tectonic plate result in unusually high elevations. Both of these regions of unusual topography or bathymetry are now well understood in the framework of the plate tectonic paradigm.
3-13. Baja California is a strip of land that has split away from the coast of Mexico just to the southeast. You should be able to fit it back into the fairly obvious niche in the Mexican coastline by moving it almost vertically down in the figure to close the Gulf of California. In the future, Baja California together with everything west of the San Andreas, will move northwest along the fault. In ten million years or so, Los Angeles will be next to San Francisco.
3-14. The Hawaiian hot spot must have been located in the vicinity of Oahu and Kauai, since the rocks on these islands formed about three million years ago. All the islands to the southeast with rocks younger than three million years had not yet been created.
3-15. The Pacific Plate is moving to the northwest, along the Hawaiian chain, with respect to the hot spot. Remember the sewing machine analogy: the islands are the "stitches" moving away from the hot spot "needle", which is currently located at the big island of Hawaii.
3-16. Fractionation refers to the separation of substances from a mixture on the basis of a physical property such as melting or boiling point. There are many commercial examples, including the recovery of pure metals from scrapped automobiles by heating scrap to progressively higher temperatures -- the metals with the lowest melting temperatures will melt first. Distillation works the same way using boiling, as in the separation of volatile gasoline from crude oil and the concentration of alcohol from a fermenting mash.
3-17. Oceanic crust is thin because it is carried away from its place of origin at the ridge crest before it can accumulate to any great thickness. At subduction zones, however, lava and magma can accumulate for a very long time on the overriding plate because it is not being destroyed.
3-18. Both the Eurasian and African Plates move toward the west as seen from the North American Plate, continuing the widening of the Atlantic Ocean.
3-19. A collision between North America and Africa brought the Appalachians to their greatest height in the Late Paleozoic. The Alps are being formed by the slow northward motion of Africa against Europe, and a Late Paleozoic collision between Europe and Asia raised the Ural Mountains of Central Russia.
3-20. The following approximate inclinations can be read directly from Figure 3-18: New Orleans, 50° down into the ground; Oslo, 75° down; Porto Alegre, 50° up out of the ground.
3-21. If the magnetic field points north and horizontal, you would be somewhere on the magnetic equator, which in most places is not far from the true equator. If the magnetic field points north and up out of the ground, then you would be somewhere in the southern hemisphere. On the basis of the information given in the question, you can't be more specific than that, since ancient longitudes are not provided by paleomagnetic data.
3-22. We can determine the ancient latitude and orientation (that is, which way was north at that time) from the magnetic field direction recorded in rocks. We cannot determine the ancient longitude.
3-23. After a magnetic polarity reversal takes place, the magnetic field at any point on Earth points in the opposite direction to that it had before the polarity flip.
3-24. Using only the ocean floor age data in the exercise you cannot determine the ancient latitudes for South America and Africa, only their relative positions with respect to one another. Paleomagnetic data from each continent will allow the ancient latitudes to be determined, however.
3-25. Gondwana consisted of the continents of South America, Africa, India, Antarctica, and Australia. It existed throughout the Paleozoic and began to break up in the Jurassic.
3-26. Essentially all of the Tethys Sea has been destroyed by subduction. We do not know of any Paleozoic ocean floor that has survived to the present day.
3-27. Your answer might include any of the following: He could not explain what were the driving forces that moved the plates; he could not explain how the continents could move through a stationary ocean floor (in fact they don't); alternate explanations were available to explain his data that were more in accord with prevailing views of the permanence of oceans and continents; he could not prove that the continents were actually moving at the present time. All of these contributed to the rejection of his theory.
3-28. There is no certain answer to this question, but plate tectonic theory cuts across the lines separating all these disciplines to such an extent, that it seems likely its development entirely within one of the disciplines would at least have been delayed severely.
3-29. Most scientists from around the world favor the free exchange of scientific data and publications among all nations. International conferences, multinational research projects, and the exchange of visiting scientists have frequently led to advances in all the sciences.
3-30. California, the intermountain seismic belt (between the Rockies and California), the Seattle area, the New Madrid area of the mid-continent, and the Charleston, South Carolina area, all are assessed as having the potential for serious seismic hazard in Figure 3-33.
3-31. Two unit steps on the Richter magnitude scale corresponds roughly to a 30 x 30 = 900 times increase in energy release.
4-1. Intraplate seismicity is found more often on the continents than on the ocean floors. See especially North America, Asia, and Africa.
4-2. In the course of melting its way through the crust, the magma mixes to a greater or lesser extent with the crustal material. Since oceanic crust is basaltic, the resulting lava is usually basaltic. In the case of continental crust, the basaltic magma from the hot spot mixes with the andesitic and granitic crustal material to produce a wide range of composition.
4-3. The active volcanism marks the current location of the hot spot, which is at the southern end of the line of volcanoes. Volcanoes produced by the hot spot have been carried away to the north.
4-4. Volatile gases, such as water vapor, dissolved in the magma produce much of the violence of the eruption. Once these gases come out of solution, the effect is that of a steam explosion.
4-5. Basaltic magma tends to contain less volatile gas in solution than andesitic magma.
4-6. Aulacogens are associated with rifting, which is an extension of the crust.
4-7. The process is very similar to what happens at the oceanic ridges. The stretched crust becomes thinner, just as a stretched bar of taffy becomes thinner. Thin crust stands at a lower elevation than thick crust (see Figure 3-5), so a valley results at the rift.
4-8. If a lithospheric block is approaching North America prior to accretion, subduction must be occurring in the region separating them in order to get rid of the intervening lithosphere. Subduction is the only process that can do this.
4-9. There has been no subduction off the United States east coast during the past 250 million years, hence no terranes could have arrived within the last 100 million years. Sea-floor spreading has been the dominant process in the North Atlantic during this time period.
4-10. Ray C' penetrates the outer core, which has a much lower P-wave velocity than the mantle. Imagine a car traveling along the path of ray C'. At the core-mantle boundary, its right wheels are in the slow-speed region of the core while its left wheels are in the high-speed region of the mantle. The result would be to pull the car around to the right, more sharply into the core. As the car emerges from the core, it is once again pulled to the right by the same effect. The rays behave in the same way.
4-11. Ray G crosses each boundary almost head-on, and so it is not deflected much either way. In the car analogy, the car drives off the end of a paved road onto a dirt road. It is slowed down, but because both left and right wheels see the change at the same time, the car continues straight ahead.
4-12. Among other geophysical reasons, the outer core is believed to be liquid because S waves cannot travel through liquids and the large S-wave shadow zone indicates that S waves cannot penetrate the outer core.
4-13. The core is metal while the mantle is rocky.
4-14. Other than the liquid water of the oceans, the only major division of the Earth that is liquid is the outer core. However, there may be small local parts of the crust and asthenosphere that are at least partially melted beneath volcanic zones.
4-15. On the average, we might expect crustal rocks to have a temperature of about 300°C at a depth of 10 km if we use the average rate of increase of 30°C per km.
4-16. (a) is an example of convection, since heat is carried by a moving medium, in this case, air. A cool breeze simply means that warmer air is being displaced (moved away) by the motion of cooler air. (b) and (c) are examples of conduction, since heat must travel out through the stationary outside wall of the house through the metal bottom of the hot iron.
4-17. Hot convecting material expands, becomes less dense, and rises, while cool convecting material contracts, becomes more dense, and sinks. The hot rising mantle material supplies heat to the volcanism of the oceanic ridges, and as it spreads apart (see Figure 4-7) encourages rifting of the spreading ridge.
4-18. Both X-rays and seismic rays can penetrate their respective subjects, and so the patterns that they produce after they have emerged allow us to deduce what is inside.
4-19. In Figure 4-18b, the convection currents move in the same direction as the plates in the upper mantle, and so help to drive them. The effect is not so clear in Figure 4-18a, where the upper mantle moves with the plates in some places, but in the opposite direction in others.
5-1. Your answer should have been something close to 6,400 km.
5-2. He noted that the shadow of the Earth cast on the Moon during a lunar eclipse is always circular. Note that if this observation is made at several different eclipses, when the Moon is in different parts of the sky for an observer, then the possibility that the Earth is a circular disk rather than spherical, is also eliminated.
5-3. Only about the width of the present Atlantic Ocean.
5-4. The merchant ship captains were familiar with the Gulf Stream and avoided it when traveling to the west. The mail packet captains did not know of it and sailed against its currents.
5-5. Nineteenth century: the sounding line. Late twentieth century: depth sounder.
5-6. The recovery of sediment and rock cores from the ocean floor.
5-7. Soft sediments.
5-8. To lower instruments, samplers, and corers <a3>into the deep ocean.
5-9. Sea level is likely to be lower when seafloor spreading rates are low because the spreading ridges have less volume and displace less ocean water onto the continental shelves.
5-10. Sediments and water.
5-11. Near the continental shelf. This is older ocean floor and so has been accumulating sediments for a longer time. Also, there is a greater supply of terrigenous sediments near the continental shelf.
5-12. At 2 mm per thousand years, it would take 500 thousand years for one meter of sediment to accumulate.
5-13. The side-scanning sonar is able to map a swath of ocean floor in one pass, while the electronic depth sounder gives depths only directly beneath the track of the ship.
5-14. A depression. The mass of rock on either side of the canyon gravitationally attracts the water away from the point directly over the canyon.
5-15. Among the unusual properties of water are: its solid state (ice) is less dense than its liquid state; its high melting and boiling temperatures; its ability to dissolve so many other substances.
5-16. Chlorine (Cl-), sodium (Na+), and sulfate (SO4--) ions are the most abundant in sea water.
5-17. Carbon dioxide (CO2).
5-18. The sodium may be supplied by river water, while much of the chlorine appears most likely to come from the mantle by way of the vents at the spreading ridges.
5-19. A region of rapid change in salinity, generally dividing the surface from the deep waters of the oceans.
5-20. The Antarctic region, providing cold, saline water that is very dense.
6-1. Direct measurements track ocean currents by observing how they move; indirect methods rely on secondary effects like the generation of electrical currents or the relation between density changes and currents.
6-2. It would produce upwelling. The effect is reversed from that shown in Figure 6-15 because the Coriolis Effect is opposite in the southern hemisphere.
6-3. The ball will be deflected to the right as seen by you, since the merry-go-round is rotating in the same sense as the Earth as seen from above the northern hemisphere. The direction that you throw the ball does not matter.
6-4. The east coast of North America is washed by the northward flowing warm currents of the Gulf Stream, while the west coast is influenced by southward flowing cold currents.
6-5. Because water has such a high heat capacity, it can absorb a large amount of heat and not increase its temperature very much. Similarly, the oceans can give up a large amount of heat and cool only slightly. The effect is to produce cooler tropics and warmer poles than would otherwise prevail.
6-6. A strong El Niño influences climate because the temperature of large areas of the sea surface is changed quite substantially. Interactions with the atmosphere produce the climatic effects.
6-7. Drought in some places, heavy rain and flooding in others; unusual storm activity.
6-8. By observing the color of the sea water.
6-9. The cores of ring currents consist of water pinched off from the other side of the Gulf Stream. Cold slope water is pinched off by a loop of the Gulf Stream and transported south into the warm Sargasso Sea.
6-10. They tend to be transparent and gelatinous, like jellyfish.
6-11. Chemical energy, probably derived from the oxidation of hydrogen sulfide.
6-12. The pressure is too great to allow steam to form. Boiling temperature increases with pressure.
7-l. The burning of coal and volcanic eruptions.
7-2. The atoms and molecules of a hot object are moving or vibrating more rapidly than those of a cool object. A hot object does not necessarily contain more heat energy than a cool object, especially if the hot object is much less dense than the cool object. If this is unclear to you, go back and review the definitions of heat and temperature in this section.
7-3. In a mercury barometer, the level of mercury in the glass tube is controlled by the pressure of the atmosphere. When the atmospheric pressure drops, the level of mercury falls; hence the expression.
7-4. Ozone absorbs ultraviolet radiant energy from the Sun, and this heat energy raises the temperature of the stratosphere.
7-5. Blue-violet light has a wavelength of 4 x 10-7 m. Using this in rule 2, we get a temperature of 6,927°C. Compare this to the much lower temperature of the red glowing coal.
7-6. The light-colored sand reflects much of the Sun's radiant energy, while the dark asphalt absorbs it, raising its temperature.
7-7. The bank of smoke or mist acts as a barrier to the escape of infrared radiation, and prevents the trees from losing as much heat during the night. In some cases, this can prevent the blossoms or fruit from freezing.
7-8. In September and April, when the Sun is directly overhead at noon. In December and June, the Sun reaches north or south of the overhead point, and its rays strike the ground at an angle less than 90°, resulting in slightly less heat. Nevertheless, the temperature would hardly change from season to season.
7-9. During the night, the land surface cools down and may become cooler than the ocean water. Air rises over the warmer water and causes a breeze blowing from land to sea. In the afternoon, sunshine has heated the land surface until it is now warmer than the ocean water and a sea breeze results.
7-10. It is being carried away by the latent heat contained in the steam. When the steam (water vapor) condenses into the fog droplets that you can see, the latent heat is released into the air.
7-11. North of the Hadley Cell, horizontal mixing of the atmosphere dominates due to the fact that the Coriolis Effect becomes stronger at higher latitudes. Rotary motion about low-pressure regions brings cold air to the south and warm air to the north, aiding the poleward flow of heat.
7-12. In the southern hemisphere summer, that is, December to April. during this time the Australian continent is warmed and a low pressure zone forms over it, pulling moist air in from the ocean to the north.
7-13. No answer necessary.
7-14. Look at Figure 7-11. Note that a cold front has a very blunt nose, with the boundary between cold and warm air rising very abruptly from the ground. The result is that the warm, moist air is forced up quickly, producing more localized cloudiness and storms. The warm front, however, is characterized by a shallow wedge of cold air overlain by warm air. The warm air is forced upward more gradually and over a larger area, producing widespread cloudiness.
7-15. Winter air is generally drier than the air during the summer, and so the potent contributions of latent heat to the energy content of a storm are much less in the winter. The powerful updrafts that form thunderheads are largely due to the energy transported by latent heat.
8-1. Regions downwind of semipermanent high-pressure zones and those downwind of major mountain ranges are two types of areas that tend to be arid.
8-2. No, the ice in a glacier always moves downhill in response to gravity. But if more ice melts near the toe than comes down from above to replenish it, the glacier will get shorter and its end (toe) will move farther up the valley. Climate changes are reflected in the growth or shrinkage of the glacier.
8-3. Patterns of thick or thin growth rings reflect benign or harsh climatic conditions during the life of the tree.
8-4. The growth ring patterns in the logs can be matched to the same patterns found in trees that were alive then and are still living today. It is then just a matter of counting the rings to determine the age of the patterns.
8-5. Because O18 does not evaporate as readily as O16, rainwater should be deficient in O18 and the O18/O16 ratio should be lower in rainwater than in ocean water.
8-6. Fortunately the two effects work in the same sense, not against one another. Note that a clam will incorporate more O18 into its shell at lower temperatures, but that a greater volume of ice will increase the O18/O16 ratio in the sea water that the clam draws upon. So a higher proportion of O18 in the clam's shell indicates either lower sea water temperature or a greater volume of ice, both of which are indicators of cooler climate. The only difficulty is precisely separating the two effects.
8-7. The glacier carries along with it boulders and rocks that act in an abrasive manner. During the passage of tens or hundreds of thousands of years, the glacier has ample opportunity to rework the landscape in a substantial way. In fact, glaciers are one of nature's most effective landscaping tools.
8-8. The arrangement of continents that tends to cut off the polar regions from the circulation of major ocean currents seems likely as at least a partial explanation for the onset of Ice Ages in the Pleistocene.
8-9. Regular and periodic changes in the Earth's orbit around the Sun.
8-10. If the initial conditions given to the model are always the same, then the predictions of the model in fact will not vary. But different results will be obtained if the initial conditions are changed. In the numerical model exercise, every student should get the same results, because the results in any step depend only on the values that were given in the top row. But if any of the initial temperatures were changed, then the results would be quite different from then on.
8-11. The results that you would have obtained in rows 1 through 5 would have been exactly the same as those you previously got in rows 6 through 10, because the results in any step depend only on the values that existed in the previous step. Notice that as you filled out the worksheet, you never had to look beyond the previous step. Similarly, in climate and weather models, if the initial conditions are sufficiently well defined, then it is not necessary to know the entire previous history of the climate system. In order to model Cretaceous climate, the geographical conditions that existed during the Cretaceous are fed into the model and it should then reproduce Cretaceous climate, provided that all the mechanisms that were operating then have been incorporated into the model.
8-12. The burning of fossil fuels (coal, oil, natural gas) and wood, deforestation, fermentation processes, and breathing.
9-1. Venus moves more quickly in its orbit because it is closer to the Sun.
9-2. Neptune.
9-3. The twinkle of stars is caused by turbulence in the Earth's atmosphere. Astronomical observations are located on mountain tops in order to be above the densest part of the atmosphere. The Space Telescope was placed in orbit so as to be above the atmosphere entirely.
9-4. Mercury and Venus are both closer to the Sun than Earth. Look at Figure 9-1b and notice that from a point on Earth's orbit, all of Venus' orbit is within 45 degrees of the Sun and Mercury's orbit is within 23 degrees of the Sun. As a result, neither planet as seen from Earth wander farther from the Sun than that angle.
9-5. Your answer might include the following: Earth rocks contain water, while Moon rocks do not; sedimentary rocks are found on Earth, but not on the Moon; metallic iron is found in Moon rocks, but not in Earth rocks; Earth rocks are usually weathered to some degree, while Moon rocks are not.
9-6. The maria are some 1.5 billion years younger than the highlands, and the number of impacting bodies was much higher prior to the basaltic flooding of the mare plains than after. By the time of the formation of the mare plains, much of the celestial bombardment was over.
9-7. There are two reasons -- Earth's oldest rocks date back to only 3.8 billion years. By this time the influx of meteorites had already slowed. Most of Earth's rocks are younger than 3 billion years, in fact. The second reason is that weathering and sedimentation on Earth has removed traces of all but a few of the craters that have formed in existing rocks.
9-8. Most of the maria are found on the hemisphere that faces us. This is probably due to a thinner crust in that hemisphere.
9-9. Comparison between the numbers of craters per <unit area for the Moon and Mercury make rough dating possible, since we have radioisotopically-dated lunar rocks. No samples have been returned from Mercury, so this is the only method available so far.
9-10. The dominant tectonic process formerly active on Mercury seems to have been shrinkage of the planet as it cooled early in its history.
9-11. The dense atmosphere with its clouds of sulfuric acid droplets makes it impossible to photograph its surface features. Detailed radar mapping of the surface has only just begun.
9-12. No, the temperature is far above the boiling point of water.
9-13. Channels eroded by running water are found in abundance on Mars. Today, all water on that planet must be frozen.
9-14. Carbon dioxide is involved in nearly all life forms found on Earth, either as a source of carbon (as in photosynthesis) or as a waste product.
9-15. The pressure in the lower atmosphere of Jupiter is so high that gaseous hydrogen changes gradually, and not abruptly, from gas to liquid.
9-16. A hurricane or other persistent cyclonic eddy in the atmosphere.
9-17. Io is close to Jupiter and derives much of its internal heat from tides raised by Jupiter. Callisto is far from Jupiter, and so its tides are very weak in comparison.
9-18. Jovian planets are large, gaseous, low in density, far from the Sun, possess many satellites, and have rings.
9-19. The rings are not solid, but are made up of millions of particles in orbit around Saturn. There is empty space between the particles.
9-20. An atmosphere rich in nitrogen.
9-21. Pluto differs from Uranus and Neptune in that it is very much smaller, and its surface is icy, not gaseous.
9-22. Meteorites found on earth have originated on both the Moon and Mars. Oblique impacts between the Moon and Mars with impacting bodies appear to have set fragments of both bodies into earth-intercepting orbits.
9-23. Many of the larger meteorites that fall to Earth have their source in the asteroid belt, while some of the smaller meteors, especially those associated with meteor showers, are probably derived from passing comets.
9-24. The iron meteorites are most like the Earth's core.
9-25. The solar wind blows the dust and gas from the solid body of the comet outward and away from the Sun. As a result, the tail can actually precede the comet when the comet is moving away from the Sun.
9-26. Larger-sized craters tend to show central peaks. On the Moon, craters smaller than about 20 km (12 mi) in diameter usually do not have them.
9-27. Plate tectonics is known to be active for <certain only on the Earth. Venus is a possibility, but more detailed examination of its surface will be needed first.
9-28. The ice worlds have smoother surfaces because ice can flow under the influence of gravity more readily than rock.
9-29. Carbon dioxide.
9-30. Biologic and oceanic processes have removed Carbon dioxide from the atmosphere and locked it up in sedimentary rocks, especially limestone and coal.
9-31. The temperature on Venus is high because of a strong Greenhouse Effect caused by its dense carbon dioxide atmosphere that admits sunlight but prevents infrared (heat) radiation from escaping to space.
10-1. The oldest dated lunar rocks and meteorites are that age. In addition, studies of uranium and lead isotope abundances on Earth indicate the same age for our planet.
10-2. These heavy elements were probably produced in one or more supernova explosions that occurred in the vicinity of the primordial nebular cloud shortly before its collapse to form the Sun and solar system.
10-3. The explosions helped to compress the original nebula to begin the accretionary process. Also, short-lived radioisotopes like Aluminum-26 were still active in the early solar system.
10-4. Earth is small compared to the Jovian planets and its weaker gravity field cannot prevent the escape of these light elements. In addition, the intense early solar wind, when the Sun first ignited, probably swept away Earth's primitive atmosphere, which well might have been rich in hydrogen and helium. Finally, most hydrogen in Earth's present atmosphere would oxidize to (H20), water.
10-5. Both are drastic but temporary effects on the worldwide climate caused by massive injection of explosion products (dust, soot, water vapor) into the atmosphere. In the case of a Nuclear Winter, the model depends largely on injection of soot and smoke particles from the burnings accompanying large numbers of separate nuclear explosions. In the case of an asteroidal collision, there is only one massive explosion that excavates far more dirt to form dust. This, together with soot from local forest fires, could produce a nuclear winter effect. On the other hand, if the impact occurred in the ocean, less rock would have been excavated and vast quantities of water vapor would have been injected into the atmosphere, possibly resulting in a temporary warming, not cooling, effect.
10-6. The chondrites are a class of meteorites whose overall composition reflects that of the solar system as a whole. They are felt to be representative of the primitive matter from which the solar system was made.
10-7. The core probably formed early in Earth history, perhaps within the first twenty million years.
10-8. The Barringer Meteorite hit the ground and produced a large impact crater, while the Tunguska body disintegrated completely in the atmosphere.
10-9. The extinction events define the boundaries between those three eras. It was precisely the patterns of dramatic change in the fossil record that prompted early geologists to assign these as the boundaries between the geological eras.
10-10. If Nemesis has an elliptical orbit that brings it near the solar system once every 26 million years it would explain the apparent cyclicity of extinctions. It would spend much of its time far from the Sun and it may be a very dim star, which would account for the fact that is has not been observed, or at least noticed.
11-1. Sheeps' fleeces were used to line sluice troughs in order to separate gold from gravel.
11-2. A mineral has a definite chemical composition, while rocks are heterogeneous mixtures of minerals that may have varying compositions.
11-3. Your answer might have included: iron, aluminum, manganese, magnesium, and titanium.
11-4. Your answer might have included: copper, lead, zinc, nickel, molybdenum, mercury, chromium, tin, tungsten, and uranium.
11-5. The steel-making industry is a heavy user of manganese.
11-6. Copper is used in the production of electrical wires, brass, and bronze.
11-7. Nitrogen, phosphorus, and potassium, are important fertilizing elements.
11-8. Oxygen and silicon are the most abundant crustal elements.
11-9. Reserves are known deposits from which minerals can be extracted profitably using existing technology under present economic conditions. Resources, on the other hand, are potential resources that might become economically viable at some future time .
11-10. Volcanism to supply magma and heat.
11-11. Gypsum, salt, potash, and borax.
11-12. Bauxite is the principal ore of aluminum and it tends to form in tropical climates with abundant rainfall.
11-13. Metallic oxides are formed on slow-spreading ridges, where the hydrothermal fluid has had a chance to mix with cold sea water. Metallic sulfides are deposited directly by the hot hydrothermal waters and are more abundant on fast-spreading ridges.
11-14. An ophiolite is a piece of oceanic crust that has been scraped off the sea floor and added to continental crust.
11-15. Hydrothermal circulation in the vicinity of igneous intrusions produced by subduction.
11-16. A back-arc basin is spreading or rifting that tends to occur immediately behind a subduction zone and separates it from a main continental landmass.
11-l7. Copper was mined in ancient Cyprus.
11-18. Hydrothermal processes were probably responsible for both deposits.
11-19. The worldwide economic downturn suppressed demand for minerals.
11-20. The former U.S.S.R. has consumed few of its mineral reserves because of its relatively low population density, and because it began with substantial reserves.
11-21. Manganese nodules are found lying on the ocean floor.
11-22. Mining or other commercial activity in Antarctica is prohibited by the Antarctic Treaty .
11-23. Substitution involves replacing expensive and scarce metal uses with metals that are cheaper and more abundant. Conservation involves cutting back on demand for raw materials by reducing unnecessary consumption, designing products for durability, and recycling used materials.
12-l. Figure 12-1 shows that 1/4 of energy use goes to transport, and of that, 3/4 goes to highway use. We may then take 3/4 of 1/4 to get 3/16 of total energy use that goes to trucks and cars.
12-2. Worldwide economic downturn and increasing prices of oil have affected recent energy use.
12-3. The term "cracking" refers to the process of breaking complex organic molecules into simpler ones.
12-4. To create petroleum, the debris from organic matter must be sealed in an anaerobic environment. Sediments accumulating on the continental shelves or sea floor provide the best environment for this process.
12-5. Oil tends to migrate toward the surface because it has a lower density than either rock or water.
12-6. An anticline is a favored structure for the trapping of oil because upward-migrating oil beneath an impermeable rock layer will travel to the highest part of the anticline's arch and become trapped there.
12-7. In the Persian Gulf region of the Middle East.
12-8. Tar sands, at least in theory, could be pumped out of the ground once they have been made less viscous by heat treating with steam. The oil in oil shale is locked into the fine sediments and must be mined before the oil can be recovered by crushing and heating the rock.
12-9. Coal forms in a terrestrial environment that is swampy and characterized by a subtropical climate and abundant rainfall, with luxuriant growth of plant matter. Oil forms most often in a shallow-water marine environment that is near abundant sources of organic matter, often from microscopic plants and animals.
12-10. An oxygen-deficient (anaerobic) environment is necessary to the production of either coal or oil.
12-11. Only a small fraction of the oil produced in rocks remains, much of it having escaped to the surface and oxidized, while most of the coal that has formed remains in the ground.
12-12. During the Carboniferous period, when much of the world's coal reserves formed, these continents were at high southern latitudes and probably endured climates too cold for the encouragement of peat bogs.
12-13. Sulfur and carbon dioxide are released in the burning of most coal. Only the sulfur can be removed by pollution control equipment.
12-14. North America holds the largest reserves of uranium.
12-15. No. The breeder reactor simply converts Uranium-238, which is not fissionable, into fissionable Plutonium-239. The supply of Plutonium-239 would be limited by Uranium-238 supplies, but these are very large compared to currently-available supplies of the Uranium-235 presently used in most nuclear reactors.
12-16. Tidal energy draws on gravitational energy, not solar radiant energy.
12-17. A present or recently active source of volcanism is required for the development of geothermal energy.
12-18. Passive solar systems utilize direct heating of the air within the living space, while active solar systems use a heat-collecting system that is mounted externally to the building and usually uses a circulating fluid.
12-19. High initial cost is the principal reason.
12-20. The last reserves to be extracted are those that are most difficult and expensive to recover, resulting in higher prices and lesser production and consumption.
12-21. Deuterium can be obtained from sea water.
13-1. Many of the early observers thought sunspots were objects passing between the Sun and Earth and not actually a part of the Sun. In addition, very few observations were made prior to the invention of the telescope.
13-2. A photon of green light has a shorter wavelength, and hence higher energy than a photon of yellow light.
13-3. Fraunhofer lines appear dark against the background of the Sun; they are due to atoms that have absorbed light that otherwise would have traveled toward Earth.
13-4. Each element has its own characteristic absorption lines in the solar spectrum. The more prominent those lines appear, the more abundant that element must be on the Sun.
13-5. They were converted into neutrons that are still in the helium nucleus. Their positive charges were carried off by two positrons. See Figure 13-3. Note in the figure that six protons are absorbed and two given off in the last stage for a net consumption of four protons.
13-6. Nuclear fusion is hard to get started because all of the particles involved are positively charged, and like charges repel one another. The particles must be brought together with enough energy to overcome this repulsion.
13-7. Only about two argon atoms are actually being produced each day. Six are expected from models of thermonuclear fusion, but only about 30% of that neutrino flux has actually been observed. Thirty percent of six is approximately two.
13-8. The temperature minimum in the chromosphere, at about 4,000°C, is the coolest part of the Sun. Temperatures climb once again in the upper chromosphere and in the corona above the chromosphere.
13-9. The Sun is divided into different layers on the basis of temperature, density, and of type of energy transport.
13-10. By excluding all but the red hydrogen-alpha emission line given off by the chromosphere, for example, the spectroheliograph can form an image of that layer of the Sun.
13-11. The depth of the convection zone and the differential rotation of the Sun's interior are two useful bits of information to come from studies of solar oscillations.
13-12. The solar wind is more intense above coronal holes because the magnetic lines of force are open in these regions -- that is, they extend from the Sun's surface far out into the surrounding space. The particles of the solar wind can travel along these lines of force to escape easily from the Sun.
13-13. Because the outer atmosphere of the Sun is a good conductor of electricity, the lines of force are rooted to the region in which they originated on the Sun. The rotation of the Sun twists the lines of force, which otherwise would have been radial, into a spiral shape.
13-14. They are cooler, hence they appear darker than the surrounding photosphere.
13-15. The strong magnetic fields in sunspots locally suppress convection, with the result that heat from the Sun's interior is not able to reach the surface so readily in the region of the spot. This results in a cooler temperature in the spot.
13-16. Sunspot numbers increase and decrease with the 11-year cycle, but the magnetic fields not associated with them change polarity once in each cycle, requiring two such cycles, or 22 years, to return to the original polarity. Thus it is the magnetic cycle that lasts 22 years.
13-17. No, sometimes temperatures in solar flares can reach high enough for nuclear reactions to take place.
13-18. In the solar corona.
14-1. Ultraviolet and extreme ultraviolet rays are absorbed by atoms and molecules in the thermosphere, causing heating. Later on, you will see that particle bombardment is an additional source of heating as well.
14-2. Atomic oxygen is formed in the upper thermosphere by the action of X-rays and extreme ultraviolet rays. In addition, it is lighter than molecular oxygen and nitrogen and so tends to rise to the top of the atmosphere along with helium, which is a very light element.
14-3. The greatest changes are found in the thermosphere; the least are found in the troposphere.
14-4. The solar wind.
14-5. The magnetopause is the boundary that separates the magnetic fields of Earth from that of the solar wind, preventing most solar wind particles from entering the near-Earth environment. The barrier is not perfect, however, and there is some leakage across the magnetopause.
14-6. The plasma sheet and the Van Allen Belts. More particles are found within the ionosphere and in a band of particles that have diffused across the magnetopause.
14-7. Increased magnetic activity produces greater heating in the thermosphere. This causes it to expand, increasing atmospheric drag on satellites.
14-8. Magnetic storms cause rapid changes in Earth's magnetic field, and these changes can induce surges of electric current in long wires that may trip circuit breakers or overload transformers.
14-9. Skylab fell sooner than expected because increasing solar activity heated and expanded the upper atmosphere, increasing atmospheric drag on the space station.
14-10. At midnight. The plasma sheet is always on the side of Earth that is opposite the Sun.
14-11. The magnetopause is the boundary that separates the magnetic fields of Earth from that of the solar wind, preventing most solar wind particles from entering the near-Earth environment. The barrier is not perfect, however, and there is some leakage across the magnetopause.
14-12. Within the auroral oval, which is a band centered on the poles. Auroral displays peak within this zone, then decrease as the poles are approached.
14-13. The particles that excite emission from gases in the ionosphere are guided by Earth's magnetic field lines; their alignment along these lines of force cause the appearance of a hanging curtain or drapery.
14-14. Oxygen and nitrogen.
14-15. Recombination of atomic oxygen is the immediate source, but atomic oxygen is produced by the action of solar radiation and energetic particle bombardment.
14-16. Increased solar activity would result in more energetic particles reaching the thermosphere, hence a greater production of nitric oxide. After a while, some of the nitric oxide would migrate down to the ozone layer where it would destroy some of the ozone present there.
14-17. Less than one percent.
14-18. Patterns of tree rings, with narrow rings indicating dry years.
14-19. Probably due to changes in the strength of the Earth's magnetic field. These are thought to be unrelated to changes on the Sun.
14-20. Solar changes are very small compared to the steady output -- less than one percent. This may be negligible compared to normal energies involved in climate variations on Earth. In addition, the mechanisms by which small solar changes can influence our climate are not sufficiently well understood to trace a cause-and-effect relation at this time.
15-1. Prokaryotes are primitive single-celled organisms that reproduce asexually by cell division. Eukaryotes are far more complex entities composed of organelles that are each as complex as a prokaryote, each performing a specific task within the cell.
15-2. The iron oxide bands indicate that Earth's atmosphere had shifted from a reducing to an oxidizing state.
15-3. They might have served as self-reproducing templates to which organic molecules could bind in regular but gradually changing patterns that might eventually develop into living organisms through the processes of natural selection.
15-4. There is only so much energy available from the carbohydrate producers, and most of it is lost to heat at each step of the food chain. The population that shares the available energy must therefore decrease with each step along the food chain.
15-5. Direct energy release from mankind's activities are likely to raise global temperatures by only about 0.5°C, but increases in "greenhouse" gases such as carbon dioxide are of much greater concern.
15-6. Carbonate sediments by far hold the greatest amount of carbon in storage.
15-7. As an omnivore, you are a consumer on the left side of the diagram. Virtually everything you eat contains carbon. Carbon leaves you in the form of bodily wastes and carbon dioxide exhaled in your breath. When you die the remaining carbon in your body will be passed on to the decomposers if you are buried or directly to the atmosphere if you are cremated.
15-8. Molecular nitrogen must be "fixed" before it can be used by the higher food chain. Nitrogen fixation occurs mostly in the soil.
15-9. Phosphates do not occur in gaseous form and so must be carried by water in nature.
16-l. Sulfur emission from coal burning and nitrogen oxides from chemical fertilizers.
16-2. Chlorofluorocarbons (CFC's) and nitrogen oxides.
16-3. No significant decrease has been detected yet, but the substances that can cause depletion are slow-acting and remain in the stratosphere for long periods of time, and can cause future depletion.
16-4. Rain shadows in the lee of mountains and persistent downwelling currents in the atmosphere that are influenced by the distribution of oceans on Earth.
16-5. Overgrazing and firewood gathering are two important factors in the spread of deserts in less-developed countries.
16-6. Increasing salinity of the soil and a high water table due to irrigation.
16-7. Carbon dioxide regulation in the atmosphere and serving as the habitat for large numbers of species are two of the ways in which tropical rain forests are important to the biosphere.
16-8. The large amount of smoke and soot injected into the atmosphere due to the burning of cities and forests.
16-9. The rising columns of heated air over destroyed cities in the northern hemisphere might reverse the flow of the northern Hadley Cell, providing a direct circulation path between the two hemispheres.
16-10. True exponential growth doubles with every passage of a fixed length of time, called the doubling time. Recent human population growth is accelerating in such a way that successive doubling times are becoming ever shorter.
16-11. During the demographic transition, death rates fall due to increased public health measures, but birth rates remain high.