This Document Contains Chapters 15 to 18 Chapter 15 The Work of Wind and Deserts Chapter Outline 15.1 Introduction 15.2 Sediment Transport by Wind 15.3 Wind Erosion 15.4 Wind Deposits 15.5 Air-Pressure Belts and Global Wind Patterns 15.6 The Distribution of Deserts 15.7 Characteristics of Deserts GEO-FOCUS 15.1: Windmills and Wind Power 15.8 Desert Landforms Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • Wind transports sediment and modifies the landscape through the processes of abrasion and deflation. • Dunes and loess are the result of wind depositing material. • Dunes form when wind flows over and around an obstruction. • The four major dune types are barchan, longitudinal, transverse, and parabolic. • Loess is formed from wind-blown silt and clay and is derived from three main sources—deserts, Pleistocene glacial outwash deposits, and river floodplains in semiarid regions. • The global pattern of air-pressure belts and winds is responsible for Earth's atmospheric circulation patterns. • Deserts are dry, receive less than 25 cm of rain per year, have high evaporation rates, typically have poorly developed soils, and are mostly or completely devoid of vegetation. • The majority of deserts are found in the dry climates of the low and middle latitudes. • Deserts have many distinctive landforms produced by both wind and running water. Chapter Summary • Desertification is the expansion of deserts into formerly productive lands. It destroys croplands and rangelands, causing massive starvation and forcing hundreds of thousands of people from their homelands. • Wind transports sediment in suspension or as bed load. Suspended load is the material that is carried in suspension by water or wind. Silt- and day-sized particles constitute most of a wind's suspended load. Bed load is the material that is too large or heavy to be carried in suspension, and is thus moved along the surface by saltation, rolling, or sliding. • Wind erodes material by either abrasion or deflation. Abrasion is the impact of saltating sand grains on an object. Ventifacts are common products of wind abrasion. • Deflation is the removal of loose surface material by wind. Deflation hollows resulting from differential erosion of surface material are common features of many deserts, as is desert pavement, which effectively protects the underlying surface from additional deflation. • Dunes are mounds or ridges of wind-deposited sand that form when wind flows over and around an obstruction, resulting in the deposition of sand grains, which accumulate and build up a deposit of sand. • Barchan, longitudinal, transverse, and parabolic are the four major dune types. The amount of sand available, prevailing wind direction, wind velocity, and amount of vegetation determine which type of dune will form. • Loess consists of wind-blown deposits of silt and clay that is derived from deserts, Pleistocene glacial outwash deposits, or river floodplains in semiarid regions. It covers approximately 10% of Earth’s land surface and weathers to a rich, productive soil. • The winds of the major air-pressure belts, oriented east-west, result from the rising and cooling of air. The winds are deflected clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere by the Coriolis effect to produce Earth's global wind patterns. • Dry climates, located in the low and middle latitudes where the potential loss of water by evaporation exceeds the yearly precipitation, cover 30% of Earth's land surface and are subdivided into semiarid and arid regions. Semiarid regions receive more precipitation than arid regions, yet are moderately dry. Arid regions, generally described as deserts, are dry and receive less than 25 cm of rain per year. • The majority of the world's deserts are in the low-latitude, dry-climate zone between 20 and 30 degrees north and south latitudes. Their dry climate results from a high-pressure belt of descending dry air. The remaining deserts are in the middle latitudes, where their distribution is related to the rain-shadow effect, and in the dry polar regions. • Deserts are characterized by high temperatures, little precipitation, and sparse plant cover. Rainfall is unpredictable and when it does occur, tends to be intense and of short duration. • Mechanical weathering is the dominant form of weathering in deserts, and coupled with slow rates of chemical weathering, results in poorly developed soils. • Running water is the major agent of erosion in deserts and was even more important during the Pleistocene, when wetter climates resulted in humid conditions. • Wind is also an erosional agent in deserts and is very effective in transporting and depositing unconsolidated fine-grained sediments. • Desert landforms include playas, which are dry lake beds, but when temporarily filled with water, form playa lakes. Alluvial fans are fan-shaped sedimentary deposits that may coalesce to form bajadas. Pediments are erosional bedrock surfaces of low relief that slope gently away from mountain bases and are covered by alluvial fans or bajadas. • Inselbergs are isolated, steep-sided erosional remnants that rise above the surrounding desert plains. Buttes and mesas are, respectively, pinnacle-like and flat-topped erosional remnants with steep sides. Enrichment Topics Topic 1. Desertification in the Sahel. Although desertification is sometimes caused by a decrease in rainfall, human activities are often to blame. Human activities, such as deforestation, intensive agriculture, and overgrazing, degrade the soil. In developing countries, the soil nutrients that were taken up by trees or animals are burned for heat and to cook food, and so the nutrients are lost and the region is unable will recover its fertility. A significant example of desertification has been in the semiarid region south of the Sahara Desert of Africa. Traditionally, the Sahel was populated by nomadic tribes, who maintained low numbers and migrated frequently, following the rains and being careful not to overgraze an area. In recent times, the nomadic tribes have been constrained to remain in one spot due to the enforcement of national boundaries and the initiation of intensive agriculture. The use of groundwater and the relative abundance of rain in the 1960s allowed the region’s population to grow. This proved disastrous when the worst drought of the century hit from 1968 to 1973. During that time, nearly 250,000 people and 3.5 million cattle died of starvation, and the Sahara expanded southward by about 100 miles (150 km). Among the western United States, sub-Saharan Africa, the Middle East, western Asia, parts of Central and South America, and Australia, more than 100,000 square miles (350,000 sq. km.) of land are lost to desertification each year. A 2004 United Nations report warns that one-third of the world’s land surface is at risk for desertification and that one-fifth of the world’s population is threatened by the impacts of this land change. Topic 2. Climatic Change in the Sahara. A desert is not always a desert, and the Sahara has not always been arid. In keeping with glacial cycles, the Sahara is sometimes humid and lush. The last humid cycle lasted from about 5,000 to 10,000 years ago, when the region was inhabited by hunter-gatherers. Some locations were relatively densely populated. As the climate became more arid, people congregated around the remaining lakes and rivers or moved south into wetter regions. Egyptian civilization came about because people congregated in the Nile River valley. http://www.thenakedscientists.com/HTML/content/interviews/interview/584/ Topic 3. Cape Wind. The Cape Wind Project is an offshore wind farm that is approved for construction in Nantucket Sound off Cape Cod in Massachusetts. The project will result in the construction of 400 foot tall wind turbines. Some locals are opposed to the wind farm because they say that it is will mar the view and be unsafe for birds. This view represents the phenomenon known as NIMBY or not-in-my-backyard. The opponents are for green power, just not in that location. Other residents and most of the people of Massachusetts are in favor of the wind farm. Even the Audubon society has endorsed it with the suggestion of further study. This is an interesting topic for a class discussion. Common Misconceptions Misconception 1: Deserts are lifeless. Fact: Although life is less abundant than in more humid areas, it is usually present. Even in Death Valley, for example, more than 600 species of plants have been identified. Misconception 2: Any desert can be farmed and made to “bloom” if only given enough water. Fact: Besides lacking water, the region may also lack appropriate soil. The soils typical of deserts, frequently containing caliche deposits, are not good for farming. Lecture Suggestions 1. An interesting topic is the different conditions that lead to the different types of deserts and the different types of vegetation that are found in each. Also, the adaptation that animals and plants have to desert conditions is a fascinating topic. 2. Global warming and the effects warmer temperatures will have on all aspects of the natural and human environment are timely and interesting topics. There are many excellent articles in New York Times and other sources. 3. Students who do not live in or near a desert have very unrealistic views of what they are. Deserts can be extremely cold at night or in winter. They may be teeming with flowers in the spring and living creatures even survive the hot summer. Most deserts are not unending oceans of sand; in fact, only about 25% of deserts are sand covered. 4. Discuss the phenomenon of NIMBY using wind power as an example. What about environmental justice? Are the people who are opposed to wind power in their back yards similarly opposed if the sites are in poor neighborhoods? 5. Show some slides of petroglyphs to the class. What can they tell us about ancient peoples? Why are they so much more prominent in deserts? Consider This 1. What is the relationship between Milankovitch orbital cycles and glacial advances? Is there a way to use Milankovitch cycles to predict the future of ice ages? Answer: Milankovitch orbital cycles, which include changes in Earth’s eccentricity, axial tilt, and precession, influence Earth's climate by altering the distribution and intensity of solar energy received. These cycles are linked to glacial advances and retreats. While they provide a framework for understanding past ice ages, predicting future ice ages requires integrating these cycles with other factors, including greenhouse gas levels. 2. How could Milankovitch cycles begin a change in climate and then how could that change in climate be accentuated by other factors such as rising greenhouse gases? Answer: Milankovitch cycles can initiate climatic shifts by changing solar radiation patterns, potentially triggering cooler temperatures that promote glacial growth. This initial cooling can be intensified by rising greenhouse gases, which trap heat and further disrupt climate patterns, leading to more pronounced climatic changes. 3. Explain the sequence of events and interrelationships of human modification, soil development, erosion, rainfall, and temperature which could transform the Brazilian rainforest into a desert. Answer: Human activities like deforestation reduce vegetation cover, leading to increased soil erosion and diminished soil quality. Reduced vegetation also lowers rainfall and increases temperatures, creating a feedback loop that can transform the Brazilian rainforest into a desert by further degrading soil and reducing moisture retention. Internet Sites, Videos, and Demonstration Aids Internet Sites 8. Desertification, http://pubs.usgs.gov/gip/deserts/desertification/ The U.S. Geolgoical Survey explores the problem of desertification, especially in the Sahara. 9. Desert U.S.A. http://www.desertusa.com/ Exploring the geology and life of the American Southwest. Videos 1. Booming Sands, NOVA science NOW, PBS online (7 mins.) How and why do some sand dunes produce strange noises? 2. The Work of the Wind. Instructional Video, DVD (20 mins.) How dunes form, various kinds of dunes and the origin of the Great Sand Dunes, Colorado. 3. Landforms of the United States. Instructional Video, DVD (30 mins.) The major physiographic provinces of the U.S. and the forces that shape each area. 4. The Geology of the Great Sand Dunes, Colorado. Instructional Video, DVD (18 mins.) The fundamentals of wind erosion and deposition set among the most impressive dunes anywhere. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 15.2 Why is only the lower part of these outcrops eroded by wind abrasion? Answer: Wind moves sand-sized particles by saltation: a series of “jumps” that pick up sand grains and move them a short distance in the wind but only about 3 feet or 1 meter above the desert floor. The yardang-like structures in Fig. 15.2 have a lower part within the sand blast zone and the upper portion extending above the “blast” zone. ❯❯ Critical Thinking Question Figure 15.6 Why is desert pavement important in desert environments? Answer: Deflation: wind erosion removes sand and fines but leaves the gravel-size particles until finally the gravel creates an armoring that prevents further deflation, stabilizing bajada and other desert surfaces so some plants can take hold and infiltration can capture ground water. ❯❯ Critical Thinking Question Figure 15.9 Did the prevailing direction of wind change during the time the sand forming these sandstone beds was deposited? Answer: Dune slip faces “face” in the direction of the wind is moving the sand: not all of these beds indicate the same wind direction based on slip face inclination angle. It does appear that there is a prevailing direction from left to right through much of these dune deposits. ❯❯ Critical Thinking Question Figure 15.13 Why do the tips of a parabolic dune point upwind and those of a barchan dune point downwind? Answer: The short answer is sand supply: barchans form where sand supply is sparse and what sand is available is carried in the dune with horns flowing in front of the main dune. Parabolic dunes form where sand is abundant and the horns trail the main body, often on beaches with lots of sand, around a blowout, and often stabilized by vegetation. ❯❯ Critical Thinking Question Figure 15.15 Although it is easy to carve hillside caves in loess, because it is unconsolidated material, what are the hazards of living in such a structure? Answer: In northern China, approximately 40 million people still live in ancient structures, called “earth houses” or “yaodongs.” The earth that surrounds the indoor space serves as an effective insulator keeping the inside of the structure warm in cold seasons and cool in hot seasons. However, loess structures are subject to collapse, due to their loose consistency, especially when moisture had intruded. ❯❯ Critical Thinking Question Figure 15.22 Why are alluvial fans that form on land the same general shape as deltas that form in water? Answer: In both, stream flow in channels is blocked by “dumped” sediment buildup within those channels by loss of competence (break in slope or standing water) and flow is deflected creating a deposit to one side or the other of the original channel deposit. Suggested Answer to Selected Short Answer Question (Answers to question 8 and question 9 provided in the appendix to the text) 6. Desertification is caused by climate change and exacerbated by human activities. Although we cannot effectively affect short-term climate change on a human time scale, what steps could be taken to reduce the desertification resulting primarily from human activities? Suggested Answer: This degradation of formerly productive land – desertification – is a complex process. It involves multiple causes, and proceeds at varying rates in different climates. Desertification became well known in the 1930s, when parts of the Great Plains in the United States turned into the "Dust Bowl" as a result of drought and poor practices in farming. Increased population and livestock pressure on marginal lands has accelerated desertification. Desertification can be addressed in a number of ways. Oases and farmlands in windy regions can be protected by planting tree fences or grass belts. More efficient use of existing water resources and control of salinization, reduction of animal grazing on marginal lands; and protection of plants from over-harvesting are also effect methods of addressing this issue. To reduce desertification driven by human activities, strategies include implementing sustainable land management practices, such as reforestation, afforestation, and soil conservation techniques. Additionally, adopting sustainable agricultural practices, like crop rotation and reduced tillage, and improving water management can help restore soil health and prevent further degradation. Education and policies supporting these measures are also crucial. Chapter 16 Oceans, Shorelines and Shoreline Processes Chapter Outline 16.1 Introduction 16.2 Exploring the Oceans 16.3 Seawater and Oceanic Circulation 16.4 Shorelines and Shoreline Processes GEO-FOCUS 16.1: Energy from the Oceans 16.5 Shoreline Erosion and Deposition 16.6 Types of Coasts 16.7 The Perils of Living Along the Shoreline 16.8 The Oceans and Economic Geology Key Concepts Review ed Learning Objectives Upon completion of this material, the student should understand the following. • Wind-generated waves and their associated nearshore currents effectively modify shorelines by erosion and deposition. • The gravitational attraction by the Moon and Sun and Earth's rotation are responsible for the rhythmic daily rise and fall of sea level known as tides. • Seacoasts and lakeshores are both modified by waves and nearshore currents, but seacoasts also experience tides, which are insignificant in even the largest lakes. • Distinctive erosional and depositional landforms such as wave-cut platforms, spits, and barrier islands are found along shorelines. • The concept of a nearshore sediment budget considers equilibrium, losses, and gains in the amount of sediment in a coastal area. • Several types of coasts are recognized based on criteria such as deposition and erosion and fluctuations in sea level. Chapter Summary • Present-day research vessels investigate the seafloor by sampling, drilling, echo sounding, and seismic profiling. Scientists also use submersibles in their studies. • The upper 100 m or so of the oceans is the photic zone where sunlight is sufficient for photosynthesizing organisms. The aphotic zone lies below. • Oceanic circulation is mostly horizontal in surface currents and deep-sea currents, but vertical circulation takes place too. • The sediments on the seafloor are mostly pelagic clay and ooze consisting of the skeletons of tiny organisms. • Moundlike, wave-resistant structures consisting of animal skeletons are reefs. Most reefs are fringing reefs, barrier reefs, or atolls. • Tides are caused by the combined effects of the Moon and the Sun on the oceans. • As wind-generated waves enter shallow water, they become oversteepened and plunge forward as breakers or spill onto the shoreline, thus expending their kinetic energy. • Longshore currents resulting from waves approaching a shoreline at an angle erode, transport, and deposit sediment. • Rip currents carry water from the nearshore zone seaward through the breaker zone. • Erosional coasts have sea cliffs, wave-cut platforms, and sea stacks, whereas depositional coasts have long sandy beaches, deltas, and barrier islands. • Beachesare continuously modified by waves and nearshore processes, and their profiles usually show seasonal changes. • Spits, baymouth bars, and tombolos all form and grow as a result of longshore transport and deposition. • The sediment budget of a nearshore system remains rather constant unless the system is disrupted, as when dams are built across streams supplying sand to the system. • Submergent and emergent coasts are defined on the basis of their relationship to changes in sea level. • Coastal flooding during storms by waves and storm surges is an ongoing problem in many areas. • The United States claims rights to all resources within 200 nautical miles of its shorelines, or what is called its Exclusive Economic Zone (EEZ). Enrichment Topics Topic 1. Submarine Canyons. Submarine canyons are like canyons on land, some as long as the Grand Canyon. They form from gravity driven water and sediments that occur almost as landslides, known as turbidity currents. In 2004, scientists “witnessed” a turbidity current when they left some scientific instruments in Monterey Canyon off of California. The canyon is 20 km offshore with a depth of 525 meters. One instrument was later found 110 m down canyon and another 400 meters down canyon. A remotely-operated vehicle ended up buried beneath a 70 cm layer of sediment 550 meters down the canyon. One instrument that was initially placed 10 km up the canyon was also swept downslope. The scientists calculated that if the turbidity current deposited 70 cm of sediment along the length of the canyon, the total material would have been 2.2 million cubic centimeters. Five other turbidity currents were measured in the canyon in the following three years. On the other coast, the Hudson Canyon off of New York, which is on a passive margin, receives only a small amount of sedimentation. The canyon was carved and received most of its sediment during the last ice age. Science News. January 1, 2005. Topic 2. Rip Currents. Rip currents form when nearshore currents move along the shore in opposite directions; where they meet, there is excess water that rushes out to sea. They are found on any beach with breaking waves and can extend out from the shoreline through the surf zone and past the breakers. More than 100 people are killed due to rip currents in the U.S. each year, and over 80 percent of rescues performed by surf beach lifeguards are on people stuck in rip currents. If you are caught in a rip current, do not try to swim in to shore; you will just become exhausted and will get pulled out to sea. Do swim parallel to the shore until you no longer feel that you are being dragged offshore. Then you should be able to safely swim inland. This may be the most practical bit of information you will learn in this course! Topic 3. How Do Scientists Learn About the Seafloor? Learning about the seafloor is difficult due to the great distances (horizontal and vertical) and tremendous amounts of water that get in the way. Research ships travel out to sea for days to months, carrying equipment that can sample sediment, rocks, and make maps. A bathymetric map shows the 3-dimensional geographic features of the seafloor on a 2-dimensional map. A device towed behind a ship sends out sound waves that strike the bottom then return. Since the speed of sound waves is known, the amount of time it takes for a wave to make a round trip allows scientists to calculate the distance to the object. When this information is compiled, a map of the seafloor emerges. A gravity corer is a hollow tube deployed on a cable that accelerates through the water. When it reaches the bottom the tube slices into the sediment so that a nicely layered sample is collected inside. Seafloor rocks are collected with a dredge, a giant rectangular bucket that is dragged behind the ship. Submersibles are small diving crafts that are not attached to the mother ship. The battery-operated submersible Alvin can descend to more than 13,000 feet (4,000 m) carrying a pilot and two passengers who collect samples, take photos and video, and make accurate descriptions of what they see. Submersibles offer scientists their best view of the deep ocean, but they are potentially dangerous and expensive. Because remotely operated vehicles (ROVs) carry no human passengers, they can visit dangerous locations. The ROV Jason, which photographed rooms inside the Titanic and Argo, has been dangerously close to hydrothermal vents. ROVs are attached to the mother ship by a fiber-optic cable that returns data and video in real time. Scientists can interpret data and make decisions on what to explore while the vehicle is at its target. Drilling is the best way to collect rocks and sediment from the seafloor because the integrity of the sediment and rock layers is maintained. The Integrated Ocean Drilling Program (IODP), an international consortium of marine research institutions, operates the drilling ship Joides Resolution. The drill cuts through the layers of sediments and rocks and returns them to the ship via the drill pipe. Common Misconceptions Misconception 1: Beaches are stable land and are suitable for development. Fact: Students believe this because there is every reason to. Barrier islands, which are really just shifting lines of sand, are heavily developed. Yet these locations are the first to suffer in a hurricane or tsunami. Even storm waves can cause great destruction. People build all manner of structures to keep the sand from moving. Students should be made aware that just because people have disregarded nature in past decades does not mean that beaches are stable or should be the site of future development. Misconception 2: Tsunami begin with a large wave of incoming water. Fact: Tsunami are large waves and as such any part of the wave can hit shore first. If the trough of the wave is the first to reach land the water will be sucked outward, leaving the beach high and dry. People sometimes make the mistake of walking onto the beach at this time because it is so strange. That is usually a fatal move as the crest of the wave will eventually come in, inundating the area. Lecture Suggestions 1. The dynamic nature of beaches can be illustrated by comparing old postcards of beach resorts with more recent photos. Likewise, old maps, navigational charts, or aerial photographs can be used to demonstrate the extent to which a shoreline may change in a relatively short period of time. 2. An interesting discussion can be held by asking students to consider the predicament of sailors in the days of wooden ships. What could they tell about the sea bottom by looking at the shoreline in unfamiliar waters? What sorts of obstacles might they encounter after a major storm? 3. Suggest that students consider how the early voyagers across the Pacific Ocean, those who travelled from Asia and Indonesia to settle in Polynesia, Micronesia, and Melanesia managed to navigate across great expanses of open seas. They had no compasses or other instruments, and certainly no maps, yet they were very successful. Aside from using stars, they also used wave refraction caused by distant, unseen land masses. 4. Compare photos of beaches from before and after the December 26, 2005 tsunami. This will illustrate examples of beach erosion. 5. Compare what we know about the oceans with what we know about the back side of the moon. Amazingly, we have a better picture of the side of the moon that never faces Earth. Have the students discuss why this might be. Consider This 1. A one-foot (30 cm) sea level rise in Florida would cause the loss of 100 feet (30 m) of beaches. What will this do for the flat-lying state? How will this affect the damage storms can do as storm surge is added to higher sea level? Answer: A one-foot sea level rise in Florida would exacerbate coastal erosion, significantly reducing beach width and increasing vulnerability to storm surge. This would heighten storm damage, as higher sea levels provide a greater base for storm surge, leading to more extensive flooding and coastal property damage. 2. During much of the Paleozoic Era and portions of the Mesozoic Era, North America and other continents were submerged beneath shallow epicontinental seas, and coastlines were submergent in character. Would the tidal range have been greater or lesser than the emergent coastlines of the present, and would the former tides have had a greater effect on shoreline features and processes? Answer: During the Paleozoic and Mesozoic Eras, submerged epicontinental seas would have led to a lesser tidal range compared to today's emergent coastlines. The reduced tidal range in these shallow seas would have resulted in less pronounced tidal effects on shoreline features compared to modern coasts. 3. Due to thermal expansion and melting glaciers, sea level has risen about eight inches (20 cm) in the past century, and the rate of upsurge has increased in recent years. In June 2006, scientists announced that the sea level rose, on average, 0.1 inches (0.3 cm) per year between 1993 and 2005. Moderate predictions of global warming also predict an increase in sea level between 0.5 m and 1.0 m by the end of the century. Ask the students: a. What regions of the world would be most severely affected by such a rise in sea level? b. What effects would such a sea level rise have on the ground water supplies of coastal cities? c. What effects would such a sea level rise have on sediment deposition at the mouths of large rivers or depositional environments such as the Mississippi Delta? d. What effects would such a sea level rise have on coastal erosion? Answer: a. Low-lying coastal regions such as Bangladesh and small island nations would be most severely affected by sea level rise. b. Rising sea levels could lead to saltwater intrusion, contaminating groundwater supplies in coastal cities. c. Increased sea levels could enhance sediment deposition at river mouths, potentially altering delta dynamics and sediment distribution. d. Higher sea levels would accelerate coastal erosion by allowing waves to reach further inland, increasing shoreline retreat. 4. If you were a real estate developer, what geologic factors should you consider before constructing homes or motels on a barrier island? Under what circumstances would you proceed with such a project? If you were a potential buyer, what questions would you ask the developer? Answer: A real estate developer should consider factors like elevation, storm surge risk, and coastal erosion potential before constructing on a barrier island. Proceed with projects if the area has robust protective measures and lower erosion risk. As a potential buyer, ask about flood risk, erosion mitigation strategies, and the long-term sustainability of the development. 5. Given the difficulty of preventing beach and coastal wetland erosion and of restoring beaches, suggest several solutions to these important problems. Answer: Solutions to beach and coastal wetland erosion include implementing artificial barriers like seawalls, groynes, and breakwaters, as well as restoring natural buffers through dune reconstruction and replanting vegetation. Coastal management should also focus on reducing human impact and promoting sustainable land use practices. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Monterey Bay Aquarium Research Institute, http://www.mbari.org/default.htm Marine research focusing particularly on the Monterey Bay area, includes news articles. 2. Coasts, http://pubs.usgs.gov/circ/c1075/contents.html The U.S. Geological Survey on coasts and some of the problems facing coasts. 3. Tide Data http://www.co-ops.nos.noaa.gov/tide_predictions.html Find tidal data for stations around the U.S. from the National Oceanic and Atmospheric Administration. 4. Circulation Movies, http://woodshole.er.usgs.gov/operations/modeling/circulation.html Animations from the U.S. Geological Survey Woods Hole Science Center. Videos 1. Hurricane Katrina: The Storm that Drowned a City. Nova, PBS Video, DVD (2005, 56 mins.) What made Katrina so deadly, the destruction the storm did, and how New Orleans is increasingly vulnerable. 2. Earth Revealed. Annenberg Media http://www.learner.org/resources/series78.html (1992, 30 mins., free video): • #24: Waves, Beaches and Shorelines 3. Planet Earth. Annenberg Media http://www.learner.org/resources/series49.html, (1986, 1 hour, free video) • #2: The Blue Planet; A Study of the Oceans. The least known part of the planet is described. 4. Educational Multimedia Visualization Center of the Department of Earth Science, free animations • Small waves http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.htmlErosion by large storm waves http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html • Wavecut terraces http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html Slides 2. Educational Images slide sets. http://www.educationalimages.com/cg120001.htm • Beach and Dune Formation and Erosion • Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 16.1 How do ocean currents modify Earth’s climate? Answer: Ocean currents carry waters warmed in tropical zones between the Tropic of Cancer and Tropic of Capricorn north or south to cooler climates where warm waters exchange energy with continental land masses and then cool currents return to the tropics like conveyor belts of energy exchange. ❯❯ Critical Thinking Question Figure 16.5 Why are there no coarse-grained (gravel and sand) sediments on the deep seafloor far from land? Answer: \In general, the sediments moved into ocean basins by stream flow dump the bed load where current slows at the base level structure (ocean basin). The clay size particles may stay in suspension longer/farther from shore, but even the fine terrigenous clastics will give way to precipitates. The one exception would include deep basin turbidites which may be coarser. ❯❯ Critical Thinking Question Figure 16.16 What is the direction of the longshore currents in this area? Answer: From this picture in Norfolk, VA, LSC is moving east to west along Chesapeake Bay; the sand is building up on the east side of the groins. ❯❯ Critical Thinking Question Figure 16.20 What will happen to the beaches in this area if a dam is built across the river? Answer: Offshore losses common in the winter must be replaced in the summer by sand from inland from streams. Dam the river, cut off the sand supply from the land side and erosion prevails along this coast. ❯❯ Critical Thinking Question Figure 16.21 Do you think a wave-cut platform is forming in this area? If so, where? Answer: The wave-cut platform is forming at the base of these cliffs and extends to at least the farthest basin-ward sea stack. Suggested Answer to Selected Short Answer Question (Answers to question 7 and question 9 provided in the appendix to the text) 8. What is wave base and how does it affect waves as they enter shallow water? Suggested Answer: The wave has a wavelength. The base of the wave is defined as half the distance of the wavelength. Wave motion is felt only at depths above the wave base, so only above the wave’s base. There is a small amount of mass transport within the orbit, an insignificant amount, until the wave reaches shallow waters. However, if the water depth is shallower than the wave base, then the orbits of particles are squashed, or more elliptical and become increasingly elliptical as you approach the bottom. Waves behave differently once they enter shallow water. Friction slows the water motion near the wave base, but water at the wave crest continues to move at the same speed and the water begins to pile up at the surface. At this point the wave can no longer support itself, and the wave breaks. The piling up and breaking of water within the surf zone generates a horizontal movement of water. This is what makes it possible for water to move objects such as surfboards forward in the surf zone. Wave base is the depth below the water's surface where wave motion becomes negligible, typically about half the wavelength of the wave. As waves enter shallow water, their base interacts with the seabed, causing the waves to slow down, increase in height, and become steeper. This interaction leads to wave breaking when the wave height exceeds its stability. Chapter 17 Geologic Time: Concepts and Principles Chapter Outline 17.1 Introduction 17.2 How Is Geologic Time Measured? GEO-FOCUS 17.1: The Anthropocene: A New Geologic Epoch? 17.3 Early Concepts of Geologic Time and Earth’s Age 17.4 James Hutton and the Recognition of Geologic Time 17.5 Relative Dating Methods 17.6 Correlating Rock Units 17.7 Absolute Dating Methods 17.8 Development of the Geologic Time Scale 17.9 Stratigraphy and Stratigraphic Terminology 17.10 Geologic Time and Climate Change Key Concepts Review Learning Objectives Upon completion of this material, the student should understand the following. • The concept of geologic time and its measurements have changed throughout human history. • The principle of uniformitarianism is fundamental to geology. • Relative dating—placing geologic events in a sequential order—provides a means to interpret geologic history. • The three types of unconformities—disconformities, angular unconformities, and nonconformities—are erosional surfaces separating younger from older rocks and represent significant intervals of geologic time for which we have no record at a particular location. • Time equivalency of rock units can be demonstrated by various correlation techniques. • Absolute dating methods are used to date geologic events in terms of years before present. Chapter Summary • Time is defined by the methods used to measure it. Relative dating places geologic events in sequential order as determined from their positions in the geologic record. Absolute dating provides specific dates for geologic rock units or events that arealso expressed in years before the present. • During the 18th and 19th centuries, attempts were made to determine Earth's age based on scientific evidence rather than revelation. Although some attempts were ingenious, they yielded a variety of ages that now are known to be much too young. • James Hutton, considered by many to be the father of modern geology, thought that present-day processes operating over long periods of time could explain all of the geologic features of Earth. His observations were instrumental in establishing the principle of uniformitarianism and the fact that Earth is much older than earlier scientists thought. • Uniformitarianism, as articulated by Charles Lyell, soon became the guiding principle of geology. It holds that the laws of nature have been constant through time and that the same processes operating today have operated in the past, although not necessarily at the same rates. • Besides uniformitarianism, the principles of superposition, original horizontally, lateral continuity, cross-cutting relationships, inclusions, and fossil succession are basic for determining relative geologic ages and for interpreting Earth history. • An unconformity is a surface of erosion, nondeposition, or both separating younger strata from older strata. These surfaces encompass long periods of geologic time for which there is no geologic record at that location. • Three types of unconformities are recognized. A disconformity separates younger from older sedimentary strata that are parallel to each other. An angular unconformity is an erosional surface on tilted or folded rocks over which younger sedimentary rocks were deposited. A nonconformity is an erosional surface cut into igneous or metamorphic rocks and overlain by younger sedimentary rocks. • Correlation is the demonstration of time equivalency of rock units in different areas. Similarity of rock type, position within a rock sequence, key beds, and fossil assemblages can all be used to correlate rock units. • Radioactivity was discovered during the late 19th century, and soon afterward, radiometric dating techniques enabled geologists to determine absolute ages for rock units and geologic events. • Absolute dates for rocks are usually obtained by determining how many half-lives of a radioactive parent element have elapsed since the sample originally crystallized. A half-life is the time it takes for one-half of the original unstable radioactive parent element to decay to a new, more stable daughter element. • The most accurate radiometric dates are obtained from long-lived radioactive isotope pairs in igneous rocks. The most reliable dates are those obtained by using at least two different radioactive decay series in the same rock. • Carbon-14 dating can be used only for organic matter such as wood, bones, and shells and is effective back to approximately 70,000 years ago. Unlike the long-lived isotopic pairs, the carbon-14 dating technique determines age by the ratio of radioactive carbon-14 to stable carbon-12. • The geologic time scale was developed primarily during the 19th century through the efforts of many people. It was originally a relative geologic time scale, but with the discovery of radioactivity and the development of radio-metric dating methods, absolute age dates were added at the beginning of the 20th century. Since then, refinement of the time-unit boundaries has continued. • Stratigraphic terminology includes two fundamentally different kinds of units: those based on content such as lithostratigraphic and biostratigraphic units, and those related to geologic time, which include time-stratigraphic and time units. • To reconstruct past climate changes and link them to possible causes, geologists must have a geologic calendar that is as precise and accurate as possible. Thus, they must be able to date geologic events and the onset and duration of climate changes as precisely as possible. Enrichment Topics Topic 1. Uniformitarianism and Catastrophism. Uniformitarianism states that the natural processes we see operating today are the same as those that operated in the past and so we can learn about the past by observing the present. Uniformitarianism recognizes that Earth changes slowly over vast periods of time. Prior to the acceptance of uniformitarianism was catastrophism, the idea that Earth was formed by sudden, short-lived catastrophic events. Catastrophism was linked to religion; Noah’s flood was a prime example of a catastrophic event, and it contrasted entirely with the idea of epeiric seas slowly encroaching over the land over a long period of time. To distinguish their ideas from the prevailing religious views, scientists rejected catastrophism entirely, and uniformitarianism as a scientific philosophy held for about two centuries. But late in the 20th century, scientists recognized that catastrophes have shaped our planet’s history. There is no better example than the asteroid impact many think caused the extinction at the end of the Mesozoic. Today, scientists combine the uniformitarianism and catastrophism into something that makes more sense as a whole. Since we see catastrophes happen (fortunately, none as bad as a massive asteroid impact), they can be a part of a uniformitarian view. The present is the key to the past and sometimes both time periods can include catastrophes. Topic 2. Climate Change in Earth’s Past. Climate change was not invented in the modern era; climate has varied tremendously in Earth’s past. Paleoclimatologists are piecing together the story of the Paleocene-Eocene Thermal Maximum (PETM), mostly from the chemistry of forams collected from ocean sediment cores. After the end of the Cretaceous Period 65 million years ago, temperatures rose until they became so high they triggered an even greater warming event around 55 million years ago, the PETM. About half of the warming, 3.6oF (2oC), took place over no more than a few hundred years and the rest over less than 5,000 years. Sea-surface temperatures increased by between 9 and 14oF (5o and 8°C), and the deep sea warmed dramatically as well. Scientists think that the most likely explanation for the warming is that a load of methane flooded the atmosphere. The most likely source of such vast amounts of methane is the methane hydrate deposits buried in seafloor sediments. According to this scenario, the PETM was triggered when ocean temperatures rose high enough that the hydrate structure melt and released the methane trapped inside. The high temperatures of the PETM had many consequences. Warm surface water caused ocean currents to switch direction. Since warm water cannot hold as much gas as cold water, oceanic oxygen levels were very low. In the atmosphere, methane broke down and formed CO2, which then formed carbonic acid that rained down and caused the carbonate shells of many organisms to dissolve. High acidity and low oxygen caused 50 percent of deep-sea forams and possibly other deep sea animals to die out. While there was no mass extinction, the abundance of some life forms and in their evolutionary pathways altered. Modern mammals from rodents to primates first evolved and flourished. The PETM lasted for about 200,000 years, likely ending when all the available methane had been released into the atmosphere. Over time, the CO2 the methane broke down into was sequestered in forests and plankton and dissolved into the oceans. Topic 3. The Oldest Known Rocks. The Acasta gneiss in northwest Canada near Great Slave Lake has been dated at 4.03 billion years of age. This age is about 100 million years older than the previous “record-holder” from western Greenland. The newly discovered rocks are of granitic composition, indicating that differentiation of continental and oceanic crust had begun before this time in Earth history because granitic rocks could not have formed directly from oceanic crust. These early continental crust samples were dated first using standard techniques applied to uranium-lead isotopic pairs contained within zircon crystals. More refined measurements were made with a sensitive high-mass-resolution ion microprobe—a machine which allows analysis of the best-preserved portions of a single crystal and is more precise than other techniques. Isolated zircon crystals dated at nearly 4.3 billion years of age have been known for some years. However, these crystals were derived from sandstones, not their granitic parent rocks. http://pubs.usgs.gov/gip/geotime/age.html Common Misconceptions Misconception 1: Earth, although old by human standards, is really very young. Also, as a consequence, the landscape has always looked pretty much the way it does now. Fact: Earth is actually much older than most people believe. Hopefully, this will be made clear in this part of the course, and this will be one idea which the students will carry away with them from the course. The landscape that we see today is in fact, geologically, very young, and only the most recent Earth has had through a seemingly endless continuum of change. Misconception 2: You can’t really trust radiometric dating of rocks. There is too much assumption involved. Fact: The basic physical principles involved in radiometric dating rely on the same knowledge of the atom which has been so convincingly demonstrated in other areas. Both the tremendous explosive power of nuclear weapons and the use of radioactive fuels in nuclear power plants depend on understanding and control of the rate of radioactive decay in nuclear reactions. Radiometric dating of rocks is just an extension of the same knowledge. Lecture Suggestions 1. Many different analogies have been used to illustrate the length of geologic time. One that was suggested in the Journal of the National Association of Geologic Teachers uses a roll of toilet paper. Bring to class a roll of toilet paper, which will represent all of geologic time, from the beginning of Earth to the present. Prepare ahead of time by determining how much time corresponds to each sheet on the roll. For example, if there are XXX sheets, each XX inches long on a roll which is XXX feet in length (this information is on the original packaging), then each sheet represents (approximately) XXX million years. Count off the required number of sheets to locate the Cenozoic/Mesozoic, Mesozoic/Paleozoic and Paleozoic/Pre Cambrian boundaries. These can be marked with “post-its” and the roll rewound before class. Have students help unwind the roll. You can also show where human history starts. 2. Discuss whether the occurrence of such events as asteroid impacts, which suddenly and globally disrupt ecosystems and the strata and sediments of a large area, invalidate the principle of uniformitarianism. 3. Note how uniformitarianism must be an accepted principle in other sciences, even though it may not be stipulated. 4. Evaluate the assertion that uniformitarianism requires that any geologic or evolutionary phenomenon which is not observable today cannot have happened in the past. 5. Consider whether or not the principle of fossil succession depends upon the existence of organic evolution. Consider This 1. Does an unconformity encompass the same duration of time everywhere it occurs? Answer: No, an unconformity does not encompass the same duration of time everywhere it occurs. The time represented by an unconformity varies depending on the specific geological context and the time gap between the layers it separates. 2. Much negative attention is often given to the sources of error and the limits of uncertainty that are given in accompaniment of any absolute age date. Why is such attention unwarranted in regard to the sources of error, and why is such attention misleading when aimed at the limits of uncertainty for any given date? Answer: Attention to sources of error in absolute age dating is necessary as it helps understand the potential inaccuracies in measurements. However, limits of uncertainty are crucial as they provide a range of possible dates, ensuring conclusions are based on probabilities rather than absolutes. 3. Does the fact that much of geology as a historical science distinguish it from other sciences in any significant way that affects the confidence one can have in its conclusions? Why or why not? Is it actually any different in its methodology than the other sciences? Answer: Geology’s historical nature involves interpreting past events from indirect evidence, which differs from experimental sciences but does not undermine confidence in its conclusions. The methodology—using observations, comparisons, and logical deductions—is consistent with other scientific disciplines. 4. A hypothetical alien interested in biology visits Earth in a time-traveling spacecraft and observes the life forms that existed in any three geologic periods. If the being could study the life of each period, but could not determine the chronometric ages of the three periods because the chronometer had malfunctioned, could that being determine a sequence for the three periods using only the observations of the life forms existing during each? If not, why? If so, how? Could the being definitively determine the correct sequence of the three periods? Why or why not? Answer: Yes, the alien could determine a sequence of the periods using observations of life forms, as fossils show evolutionary progression. By identifying which life forms evolved from others, the alien could establish a relative sequence, though it might not be able to determine absolute ages without chronometric data. 5. Why can fossils be used to demonstrate the age equivalence of geographically separated and (often) lithologically dissimilar strata? Answer: Fossils enable age equivalence by providing a record of evolutionary changes across different regions. Correlation of fossils from different locations helps match strata of similar ages, even if the rocks are lithologically distinct. 6. Is there any single region on Earth that has a complete rock record? Answer: No, there is no single region on Earth with a complete rock record. Geological processes such as erosion, metamorphism, and tectonics often lead to gaps and missing intervals in the rock record. Internet Sites, Videos, and Demonstration Aids Internet Sites 1. University of California, Museum of Paleontology, http://www.ucmp.berkeley.edu/exhibit/geology.html An introduction to all of the geologic time periods, the evolution of life and the geologic time scale from the University of California, Berkeley. 2. Grand Canyon Geology http://www.nps.gov/grca/naturescience/geologicformations.htm Lots of websites deal with the Geology of the Grand Canyon. This is one by the National park Service. Videos 1. American Experience: Lost in the Grand Canyon. PBS DVD (1999, 53 mins.) The journey of Josh Wesley Powell in the spring of 1869 down the Colorado River through the Grand Canyon. 2. Earth Revealed #10: Geologic Time. Annenberg/CPC Collection. All of Earth history compressed down to a year including major geologic events and a timeline for life on Earth. 3. Fossils, Rocks and Time. Insight Media (2005, 32 mins.) The geologic time scale and the rocks and fossils that have led to its development. 4. Geologic Time. Insight Media (2000, 25 mins.) An introduction to the geologic time scale and potassium-argon radiometric dating. Slides 1. Educational Images, slide sets, http://www.educationalimages.com/it120015.htm a. Geologic Time and Evolution b. Sediments, Faults and Unconformities c. Fossils and Fossilization Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 17.5 In (b), it is stated that the sill is younger than beds 2 and 3, but its age relative to beds 4–6 cannot be determined. Why is this? Answer: The beds 4-6 could have been deposited after the intrusion of the sill. In Figure 17.5(b), the sill is stated to be younger than beds 2 and 3 because it intruded after these beds were deposited. However, the age of the sill relative to beds 4–6 cannot be determined because there is no direct evidence of the sill’s relationship with these beds, such as cross-cutting relationships or observable contacts, that would establish a clear temporal sequence. ❯❯ Critical Thinking Question Figure 17.10 From what you can see in this photo, which is the same scene Hutton viewed in 1788, what evidence is there that this outcrop represents an ancient mountain range? Were the forces compressional or tensional? Answer: Orogeny – mountain building: folding and faulting, igneous intrusion & yes – compression that forms deformation perpendicular to those forces, causing uplift. In Figure 17.10, the evidence that the outcrop represents an ancient mountain range includes the presence of folded and metamorphosed rock layers, which indicate significant deformation and compression. The tight folding and complex structures suggest that the forces involved were compressional, characteristic of the tectonic activity associated with mountain building. ❯❯ Critical Thinking Question Figure 17.14 Can you give at least one explanation for why the lower tongue of sandstone present in the left and center columns does not reach all the way to the column on the right? Answer: The Principle of Lateral Continuity, facies changes that reflect differences in water depth, and others. One explanation for why the lower tongue of sandstone in the left and center columns does not extend to the right column is that the sandstone may have been deposited in a non-continuous environment, such as a changing shoreline or shifting sediment supply. This interruption could have been caused by erosion, a change in depositional conditions, or a hiatus in sedimentation that created a gap in the sandstone tongue’s continuity. ❯❯ Critical Thinking Question Figure 17.25 Why do you think the ratio of carbon 14 to carbon 12 is constant in living organisms? Answer: The beta decay occurs after death; with C14 & not C12. The ratio of carbon-14 to carbon-12 is constant in living organisms because carbon-14 is continuously exchanged with the environment through processes like respiration and photosynthesis. This balance maintains a consistent ratio while the organism is alive, as the uptake of carbon from the atmosphere keeps the ratio stable relative to the atmospheric levels of carbon-14 and carbon-12. ❯❯ Critical Thinking Question Figure 17.28 Why don’t the biozone boundaries correspond with the lithostratigraphic boundaries? Answer: Organisms may, especially cephalopods, may live in multiple ranges of marine depths where variable sediment types occur. Biozone boundaries don’t correspond with lithostratigraphic boundaries because biozones are defined by the presence of specific fossils, which reflect changes in biological conditions over time. Lithostratigraphic boundaries, on the other hand, are based on changes in rock types and sedimentary environments. These fossil-based and rock-based criteria can vary independently due to different rates of sedimentation, fossil preservation, and environmental changes. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 9 provided in the appendix to the text) 7. Why were Lord Kelvin’s arguments and calculations so compelling, and what was the basic flaw in his assumption? What do you think the course of geology would have been if radioactivity had not been discovered? Suggested Answer: Lord Kevin had empirical evidence supporting his hypothesis, namely, that the temperature of Earth increased with increasing depth. Given that evidence from deep mining in Europe could not be refuted, and also given that his calculations were sound, his estimate of the age of Earth seemed correct, except that it was much younger than supposed. However, his basic premise was flawed in that he failed to take radioactivity into account, which is an inner heat source for Earth. Lord Kelvin’s arguments were compelling due to his rigorous application of thermodynamics and his use of empirical data to estimate the Earth's age. The basic flaw in his assumption was his disregard for the heat generated by radioactive decay, which significantly affects Earth's thermal history. Without the discovery of radioactivity, geology would have likely continued to rely on inaccurate estimates of Earth’s age, delaying the development of modern geological and evolutionary theories. Chapter 18 Organic Evolution—The Theory and Its Supporting Evidence Chapter Outline 18.1 Introduction 18.2 Organic Evolution: What Does It Mean? GEO-INSIGHT 18.1: Artificial Selection, Natural Selection, Fossils, and Evolution 18.3 Mendel and the Birth of Genetics 18.4 The Modern View of Organic Evolution 18.5 Evidence Supporting Evolutionary Theory GEO-FOCUS 18.1: Building a Dinochicken Learning Objectives Upon completion of this material, the student should understand the following. • The central claim of the theory of evolution is that today's organisms descended, with modification, from ancestors that lived in the past. • In 1809, Jean-Baptiste de Lamarck proposed inheritance of acquired characteristics to account for evolution. • In 1859, Charles Darwin and Alfred Wallace published their views on evolution and proposed natural selection as the mechanism to account for evolution. • During the 1860s, Gregor Mendel demonstrated that variations in populations are maintained rather than blended, as previously thought, during inheritance. • In the modern view of evolution, sexual reproduction and mutations in sex cells account for most variation in populations, and populations rather than individuals evolve. • The fossil record provides many examples of macroevolution—changes resulting in the origin of new species, genera, and so on—but these changes are simply the cumulative effect of microevolution, which involves changes within a species. • Evolutionary trends such as size increase and changes in shells, teeth, and bones are well known for organisms for which sufficient fossils are available. Chapter Summary • Jean-Baptiste de Lamarck's proposal of inheritance of acquired characteristics was the first formal explanation for the theory of evolution to be taken seriously. • In 1859, Charles Robert Darwin and Alfred Russel Wallace published their views on evolution and proposed natural selection as the mechanism for evolutionary change. • Darwin's observations of variation in natural populations and artificial selection, as well as his reading of Thomas Malthus's essay on population, helped him formulate the idea that natural processes select favorable variants for survival. • Gregor Mendel's breeding experiments with garden peas provided some of the answers regarding how variation is maintained and passed on. • Genes are the hereditary determinants in all organisms. This genetic information is carried in the chromosomes of cells, but only the genes in the chromosomes of sex cells are inheritable. • Sexual reproduction and mutations account for most variation in populations. • Evolution by natural selection is a two-step process. First, variation must be produced and maintained in interbreeding populations, and second, favorable variants must be selected for survival. • An important way in which new species evolve is by allopatric speciation. When a group is isolated from its parent population, gene flow is restricted or eliminated, and the isolated group is subjected to different selection pressures. • Divergent evolution involves an ancestral stock giving rise to diverse species. The development of similar adaptive types in different groups of organisms results from parallel and convergent evolution. • Microevolution involves changes within a species, whereas macroevolution encompasses all changes above the species level. Macroevolution is simply the outcome of microevolution over time. • Scientists are increasingly using cladistic analyses to determine relationships among organisms. • Extinctions take place continually, and times of mass extinctions resulting in marked decreases in Earth's biologic diversity have occurred several times. • The theory of evolution is truly scientific because we can think of observations and experiments that could support or falsify it. • Much of the evidence supporting the theory of evolution comes from classification, embryology, genetics, biochemistry, molecular biology, and present-day small-scale evolution. • The fossil record also provides evidence for evolution in that it shows a sequence of different groups appearing through time, and some fossils show features that we would expect in the ancestors of birds or mammals, and so on. Enrichment Topics Topic 1. Adaptive Radiation of Darwin’s Finches. Peter and Rosemary Grant have been studying Darwin’s finches in the Galapagos for more than 30 years, far longer than Darwin! They have identified 14 or 15 species that evolved from the same common ancestor, a seed eater from South America. While Darwin’s finches present a beautiful example of adaptive radiation, the model is not one of a tree that branches out into smaller and smaller branches and twigs. In this instance, the tree is lopsided, with the main trunk splitting into three main branches, only one of which breaks into several branches and many twigs. The other trunk produces only some thin twigs. For the adaptive radiation of Darwin’s finches, the Grants describe a model of allopatric speciation, in which a small population separates from the main population (in this case by colonizing a new island) and evolves to meet the demands of its new environment, eventually becoming a new species. If the species later come back into contact, they may coexist, if they have diverged sufficiently and are not in competition. The Grants were the subject of a 1995 Pulitzer Prize winning book, The Beak of the Finch, by Jonathan Weiner. Topic 2. Genetic Engineering and Evolution. Evolution proceeds because of genetic diversity within a population—alleles for various traits exist within a population and certain alleles will be more frequently expressed when they code for the best trait possible for existing conditions. People have furthered evolution for centuries by selectively breeding organisms that had favorable traits to increase the expression of those traits in a population. Now scientists have a more direct route to this sort of change using genetic engineering. In this technique, scientists can place a desired allele in the DNA of an organism, even if the allele is from a completely different species. For example, adding pesticide resistance from an insect into a food crop strain. Using this technology, medical breakthroughs are possible for diseases such as diabetes and cystic fibrosis. Of great concern to some people is the genetic engineering of plants and animals for foods. It has already happened that some of those organisms have escaped into the wild (after all, it is impossible to restrict pollen from going where it is blown). How much will genetically modified organisms disrupt natural ecosystems? What will be the effects of these organisms when they mix with traditional food crops? Also, the purpose of genetic modification is to allow only the desired traits to be expressed. How much does this restriction of genetic diversity affect the organisms’ ability to evolve in the future, especially when, as appears to be happening, other strains of food crops are allowed to die out? Topic 3. Ask a Biologist. Ask someone who teaches introductory biology or evolutionary theory and they will likely say that the Linnean system of classification is going the way of the dinosaur and cladistics is coming in. Cladistics focuses on shared derived characteristics. More emphasis is being put on genetic sequencing and computational phylogenetics in classifying organisms since many genomes have now been sequenced. Find the current thoughts on this to share with the class. Common Misconceptions Misconception 1: Scientists do not agree that evolution by natural selection is the way organisms come to be. Fact: Nearly all biologists agree that evolution by natural selection is true and accurate. The dissention is in the details, such as with the rate of change of evolutionary processes, not with the framework of the theory. Misconception 2: All the large animals that lived in the past were “dinosaurs.” Fact: Dinosaurs included the Mesozoic reptiles which belonged to the groups designated ornithiscians and saurischians. Some of these animals would, indeed, have seemed quite frightening and monstrous to us today. But many of the dinosaurs were quite small and probably timid in behavior. In addition, many extinct animals are often lumped in with the dinosaurs in popular films and literature. Examples of the latter animals include mammoths, saber-toothed cats, and dire wolves, none of which are reptilian or lived in the Mesozoic. Lecture Suggestions 1. This is a good time to review the scientific method. What is a theory? What makes it different from a law? What makes science different from faith-based explanations of the world? 2. One of the major difficulties in teaching evolutionary theory is providing beginning students with adequate information concerning the vast amount of accumulated evidence in favor of the modern theory. An effort should be made to emphasize this and that understanding evolution requires a strong foundation in both biology and geology. 3. Be prepared for students to say they do not “believe” in evolution. After explaining the differences between how science and faith differ, be sure you understand evolutionary theory well enough that you can respond to those students arguments. Although you may never change the mind of a true creationist, the other students will hear your well-founded arguments and have a better footing for their own internal and external arguments. 4. Make use of some of the well-studied fossil suites such as the horse or ammonoids to illustrate how scientific theory evolves. 5. It is estimated that there are about 5 million species of plants and animals today. G.G. Simpson estimated that the average life span of a single species ranges between 0.5 and 5 million years. Using an average lifespan of 3 million years and assuming that the level of diversity since the Cambrian is similar to that of today, we can calculate the total number of species that have risen since the Cambrian, 600 million years ago: (5 × 106) (600 × 106) 3 × 106 = 109 Compare these 1 billion species with the approximately 150,000 known fossil species present in the geological record. Thus, about 0.015 percent of all possible species have been recorded in the preserved and identifiable fossil record. 6. Emphasize the selective preservation of organisms by creating analogies. The chances of a living organism being fossilized might be comparable to winning a lottery. The odds are extremely high against you unless conditions are right. For an organism, the correct conditions of burial are critical. Organisms that live in a marine environment tend to have greater chances of being buried in sediment than land dwelling organisms. Insects comprise about 1,000,000 species, yet there are only about 12,000 insect species known from the fossil record. 7. The late Dr. Stephen J. Gould’s book Wonderful Life is excellent for anyone teaching historical geology. The book focuses on two separate but related stories. First, there is the story of the phenomenal Cambrian explosion of life documented in the Burgess Shale. Second, there is the story of how scientific thought evolves and why it took so long for the story of the Burgess Shale and its fauna to be fully appreciated. This book should also be considered for a lecture supplement for teaching Chapter 11 “Geology of the Early Paleozoic Era.” In this book, Gould explores the concept of contingencies or the “what if” factor. What would life be like today had the phyla that evolved from the Early Cambrian died out and the phyla that did not survive this early explosion hadn’t died out? Would humans be on this different Earth? Consider This 1. Consider the important concept of extinction. Given the number of species that have become extinct through geologic time, is it really important for humans to try to save all endangered species? How about large numbers of species? Answer: While extinction is a natural process, the current rate of species loss is accelerated by human activities, which can disrupt ecosystems and diminish biodiversity. Saving endangered species is crucial for maintaining ecological balance, as each species plays a role in its ecosystem. Preserving large numbers of species ensures ecosystem resilience and functionality, which are vital for human well-being and the health of our planet. 2. Is there any way to determine which species should be protected and which may not be important in the long run? Are humans too focused on “charismatic megafauna”—a.k.a. big, pretty animals—rather than on species that may be important to their ecosystems? Answer: Determining which species to protect involves assessing their ecological roles, such as their impact on ecosystem stability and services. While "charismatic megafauna" often receive more attention, smaller or less visible species can be equally crucial for ecosystem health. Effective conservation should balance protecting iconic species with preserving key ecological functions provided by less charismatic but ecologically significant species. 3. How would Darwin’s conclusions about evolution have been influenced if he had information concerning the cellular basis of heredity? Answer: If Darwin had known about the cellular basis of heredity, his conclusions on evolution might have been more detailed and precise. Understanding genes and chromosomes would have provided a clearer mechanism for how traits are inherited and vary, potentially refining his theory of natural selection by integrating the genetic basis of variation and inheritance. 4. Why can fossils be used to demonstrate the age equivalence of geographically separated and (often) lithologically dissimilar strata? Answer: Fossils can demonstrate age equivalence across geographically separated and lithologically dissimilar strata because they provide evidence of specific time periods through the presence of particular species. Correlation of index fossils, which are widespread and short-lived, allows geologists to match strata of similar ages regardless of rock type variations. Internet Sites, Videos, Software, and Demonstration Aids Internet Sites 1. Evolution: A Journey into Where We’re From and Where We’re Going, PBS http://www.pbs.org/wgbh/evolution/ 2. Understanding Evolution: Your One-Stop Shop for Information on Evolution http://evolution.berkeley.edu/ 3. University of California Museum of Paleontology Evolution Wing http://www.ucmp.berkeley.edu/history/evolution.html 4. The TalkOrigins Archive – Exploring the Creation/Evolution Controversy http://www.talkorigins.org Videos 1. Earth Revealed #10: Geologic Time. Annenberg/CPC Collection. 2. Evolution. PBS VHS 3. Scientific American Frontiers: Voyage to the Galapagos, PBS VHS. 4. Darwin’s Dangerous Idea. Insight Media 5. Darwin’s Path to the Theory of Evolution. Insight Media. 6. Elements of Biology: Biological Evolution. Insight Media. 7. Evolution. Insight Media 8. Evolution and Phylogenetics. Insight Media. 9. The History of Evolutionary Theory. Insight Media. 10. How Does Natural Selection Produce New Species? Insight Media. 11. Icons of Science: Evolution. Insight Media 12. Macroevolution. Insight Media. 13. Microevolution. Insight Media. 14. Origin of Species: Charles Darwin. Insight Media. 15. Origin of Life and Evolution of a Theory. Insight Media. 16. The Process of Evolution. Insight Media. 17. Understanding Evolution. Insight Media. 18. What is Evolution by Natural Selection? Insight Media Slides 1. Geological Time and Evolution. Educational Images, Ltd. 2. Answers to Figure-Related Critical Thinking Questions ❯❯ Critical Thinking Question Figure 18.3 Can you think of other examples of artificial selection in plants and animals? Answer: Many examples of artificial selection exist. Examples include domesticated animals such as the various breeds of dogs, cats, horses, cows, chickens, and several others. ❯❯ Critical Thinking Question Figure 18.4 Using the third generation, what would be the possible fourth generation offspring if Aa and aa are cross-fertilized? Answer: The fourth generation (with a breeding of Aa and aa) would show 50% Aa and 50% aa. The phenotypes would be two plants with red flowers and two plants with white flowers. ❯❯ Critical Thinking Question Figure 18.10 Is this sequence of fossil titanotheres consistent with any of the predictions in Table 18.1? If so, which one(s)? Answer: This fossil record shows consistency with the following predictions in Table 18.1: 1, 3 and 5. Without viewing Figure 18.10 or Table 18.1, a general answer is that if the sequence of fossil titanotheres shows a progressive change in features over time, it aligns with the prediction of gradual evolutionary change from Table 18.1. This would be consistent with the idea that fossils demonstrate a chronological sequence reflecting evolutionary development. ❯❯ Critical Thinking Question Figure 18.15 How does the presence of homologous structures in the wings of bats and birds, based on their skeletal features, support the concept of common ancestry in evolutionary biology? Answer: The wings of the bat and bird are homologous structures as they are based on skeletal features. Suggested Answer to Selected Short Answer Question (Answers to question 6 and question 10 provided in the appendix to the text) 9. Does natural selection really mean only the biggest, strongest, and fastest will survive and reproduce? Suggested Answer: No, not at all. Natural selection indicates that organisms showing advantageous adaptations will live long enough to reproduce and thus, their genes will be carried into the genome of the population. No, natural selection does not only favor the biggest, strongest, and fastest. It acts on traits that increase an organism's overall fitness in a given environment. Traits that enhance survival and reproduction, such as adaptability, resourcefulness, and reproductive success, can be just as important as physical size or speed. Solution Manual for The Changing Earth: Exploring Geology and Evolution James S. Monroe, Reed Wicander 9781285733418
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