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1 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” To advance through the presentation, click the right-arrow key or the space bar. From the resources slide, click on any resource to see a presentation for that resource. From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. You may exit the slide show at any time by pressing the Esc key. How to Use This Presentation

2 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter Presentation TransparenciesStandardized Test Prep Visual Concepts Resources Brain Food Video Quiz

3 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Rock Record Chapter 8 Table of Contents Section 1 Determining Relative Age Section 2 Determining Absolute Age Section 3 The Fossil Record

4 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Objectives State the principle of uniformitarianism. Explain how the law of superposition can be used to determine the relative age of rocks. Compare three types of unconformities. Apply the law of crosscutting relationships to determine the relative age of rocks.

5 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Uniformitarianism uniformitarianism a principle that geologic processes that occurred in the past can be explained by current geologic processes Geologists estimate that Earth is about 4.6 billion years old, an idea that was first proposed by James Hutton in the 18th century. Hutton theorized that the same forces that change Earth’s surface now, such as volcanism and erosion, are the same forces that were at work in the past.

6 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Uniformitarianism, continued Earth’s Age Hutton’s ideas raised serious questions about Earth’s age, because up until that time, most scientists thought Earth was only 6,000 years old, and that all Earth’s geologic features had formed at the same time. Hutton’s ideas about uniformitarianism encouraged other scientists to learn more about Earth’s history.

7 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Reading check, continued What evidence did Hutton propose to show that Earth is very old?

8 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Reading check, continued What evidence did Hutton propose to show that Earth is very old? Hutton reasoned that the extremely slow-working forces that changed the land on his farm has also slowly changed the rocks that make up Earth’s crust.

9 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Relative Age, continued relative age the age of an object in relation to the ages of other objects One way to learn about Earth’s past is to determine the order in which rock layers and other rock structures formed. Layers of rock, called strata, show the sequence of events that took place in the past.

10 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Relative Age, continued Scientists can determine the order in which rock layers formed by using a few basic principles. Once they know the order, a relative age can be determined for each layer. Relative age indicated that one layer is older or younger than another layer but does not indicate the rock’s age in years.

11 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Law of Superposition, continued law of superposition the law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed Scientists commonly study the layers in sedimentary rocks to determine the relative age of rocks. Sedimentary rocks form when new sediments are deposited on top of old layers of sediment. As the sediments accumulate, they harden into layers called beds. The boundary between two beds is called a bedding plane.

12 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Law of Superposition, continued Scientists use a basic principle called the law of superposition to determine the relative age of a layer of sedimentary rock. The law of superposition states that an undeformed rock layer is older than the layers above it and younger than the layers below it.

13 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Law of Superposition, continued The diagram below illustrates the law of Superposition. Section 1 Determining Relative Age

14 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Principle of Original Horizontality Scientist know that sedimentary rock generally forms in horizontal layers. The principle of original horizontality states that sedimentary rocks left undisturbed will remain in horizontal layers. So, scientists can assume that sedimentary rock layers that are not horizontal have been tilted or deformed by crustal movements that happened after the layers formed.

15 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Principle of Original Horizontality, continued Graded Bedding In some cases, tectonic forces push older layers on top of younger ones or overturn a group of rock layers. So, scientists must look for clues to the original position of the layers. One clue is the size of particles in the layers. In some environments, the largest particles of sediment are deposited in the bottom layers.

16 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Principle of Original Horizontality, continued Graded Bedding The arrangement of layers in which coarse and heavy particles are in the bottom layers is called graded bedding. If larger particles are located in the top layers, the layers may have been overturned by tectonic forces.

17 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Principle of Original Horizontality, continued Cross-Beds Another clue is the shape of the bedding planes. When sand is deposited, sandy sediment forms curved beds at an angle to the bedding plane. These beds are called cross-beds. Scientists can study the shape of the cross-beds to determine the original position of the layers.

18 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Principle of Original Horizontality, continued Ripple Marks Ripple marks are small waves that form on the surface of sand because of the action of water or wind. When the sand becomes sandstone, the ripple marks may be preserved. In undisturbed sedimentary rock layers, the crests of the ripple marks point upward. Scientists study the orientation of the ripple marks to determine the original position of the layers.

19 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Reading check, continued How can ripple marks indicate the original position of rock layers?

20 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Reading check, continued How can ripple marks indicate the original position of rock layers? Because ripple marks form at the top of a rock layer, scientists can use the orientation of the ripple marks to determine which direction was “up” when the rock layers formed.

21 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Unconformities, continued unconformity a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time Movements of Earth’s crust can lift up rock layers that were buried and expose them to erosion. Then, if sediments are deposited, new rock layers form in place of the eroded layers. The missing layers create a break in the geologic record, called an unconformity.

22 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Unconformities, continued There are three types of unconformities. A nonconformity is an unconformity in which stratified rock rests upon unstratified rock. An angular unconformity is the boundary between a set of tilted layers and a set of horizontal layers. A disconformity is the boundary between horizontal layers of old rock and younger, overlying layers that are deposited on an eroded surface.

23 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Types of Unconformities, continued The diagram below illustrates the three types of unconformities. Section 1 Determining Relative Age

24 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Determining Relative Age Chapter 8 Unconformities, continued Crosscutting Relationships law of crosscutting relationships the principle that a fault or body of rock is younger than any other body of rock that it cuts through. A fault is a break or crack in Earth’s crust along which rocks shift their position. An intrusion is a mass of igneous rock that forms when magma is injected into rock. In these cases, scientists use the law of crosscutting relationships, or the fact that a fault or an intrusion is always younger than the layers it cuts through, to determine the order of the layers.

25 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Crosscutting Relationships, continued The law of crosscutting relationships can be used to determine the relative ages of rock layers. Section 1 Determining Relative Age

26 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Objectives Summarize the limitations of using the rates of erosion and deposition to determine the absolute age of rock formations. Describe the formation of varves. Explain how the process of radioactive decay can be used to determine the absolute age of rocks.

27 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Absolute Dating Methods absolute age the numeric age of an object or event, often stated in years before the present, as established by an absolute-dating process, such as radiometric dating Scientists use a variety of ways to determine absolute age, or the numeric age, of a rock formation.

28 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Absolute Dating Methods, continued Rates of Erosion One way scientists use to estimate absolute age is to study rates of erosion. Studying the rates of erosion is practical only for geologic features that formed within the past 10,000 to 20,000 years. For older surface features, the method is less dependable because rates of erosion can vary over millions of years.

29 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Absolute Dating Methods, continued Rates of Deposition Scientists can also estimate absolute age by calculating the rate of sediment deposition. By using data collected over a long period of time, geologists can estimate the average rates of deposition for common sedimentary rocks. This method is not always accurate because not all sediment is deposited at an average; therefore it provides only an estimate of absolute age.

30 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Absolute Dating Methods, continued Varve Count varve a banded layer of sand and silt that is deposited annually in a lake, especially near ice sheets or glaciers, and that can be used to determine absolute age. Some sedimentary deposits show definite annual layers, called varves. The varves can be counted much like tree rings to determine the age of the sedimentary deposit.

31 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Reading check How are varves like tree rings?

32 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Reading check, continued How are varves like tree rings? Varves are like tree rings in that varves are laid down each year. Thus, counting varves can reveal the age of sedimentary deposits. Section 2 Determining Absolute Age

33 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating radiometric dating a method of determining the absolutes age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope. Rocks generally contain small amounts of radioactive material that can act as natural clocks. Atoms of the same element that have different numbers of neutrons are called isotopes. Radioactive isotopes can be used to determine age.

34 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Radioactive isotopes have nuclei that emit particles and energy at a constant rate regardless of surrounding conditions. Scientists use the natural breakdown of isotopes to accurately measure the absolute age of rock, which is called radiometric dating. To do this, scientists measure the concentration of the parent isotope or original isotope, and of the newly formed daughter isotopes. Then, using the known decay rate, they can determine the absolute age of the rock.

35 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Radiometric Dating Section 2 Determining Absolute Age

36 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Half-Life half-life the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope. Scientists have determined that the time required for half of any amount of a particular radioactive isotope to decay is always the same and can be determined for any isotope.

37 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Half-Life By comparing the amounts of parent and daughter isotopes in a rock sample, scientists can determine the age of the sample. The greater the percentage of daughter isotopes present in the sample, the older the rock is.

38 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Radioactive Decay and Half-Life, continued Section 2 Determining Absolute Age

39 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Half-Life Section 2 Determining Absolute Age

40 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Radioactive Isotopes Uranium-238, or 238 U, is an isotope of uranium that has an extremely long half-life, and is most useful for dating geologic samples that are more than 10 million years old. Potassium-40, or 40 K, has a half-life of 1.25 billion years, and is used to date rock that are between 50,000 and 4.6 billion years old.

41 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Radioactive Isotopes Rubidium-87 has a half-life of about 49 billion years, and is used to verify the age of rocks previously dated by using 40 K.

42 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Reading check How does the half-life of an isotope affect the accuracy of the radiometric dating method?

43 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Reading check, continued How does the half-life of an isotope affect the accuracy of the radiometric dating method? An isotope that has an extremely long half-life will not show significant or measurable changes in a young rock. In a very old rock, an isotope that has a short half-life may have decayed to the point at which too little of the isotope is left to give an accurate age measurement. So, the estimated age of the rock must be correlated to the dating method used. Section 2 Determining Absolute Age

44 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Carbon Dating Younger rock layers may be dated indirectly by dating organic material found within the rock. Organic remains, such as wood, bones, and shells that are less than 70,000 years old can be determined by using a method known as carbon-14 dating, or radiocarbon dating.

45 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Determining Absolute Age Chapter 8 Radiometric Dating, continued Carbon Dating All living organisms have both the carbon-12 and carbon-14 isotope. To find the age of a sample of organic material, scientists compare the ratio of 14 C to 12 C and then compare this with the ratio of 14 C to 12 C known to exist in a living organism. Once a plant or animal dies, the ratio begins to change, and scientist can determine the age from the difference between the ratios of 14 C to 12 C in the dead organism.

46 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Objectives Describe four ways in which entire organisms can be preserved as fossils. List five examples of fossilized traces of organisms. Describe how index fossils can be used to determine the age of rocks.

47 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Interpreting the Fossil Record fossils the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock paleontology the scientific study of fossils Fossils are an important source of information for finding the relative and absolute ages of rocks. Fossils also provide clues to past geologic events, climates, and the evolution of living things over time.

48 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Interpreting the Fossil Record, continued Almost all fossils are discovered in sedimentary rock. The fossil record provides information about the geologic history of Earth. Scientists can use this information to learn about how environmental changes have affected living organisms.

49 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Fossilization Only dead organisms that are buried quickly or protected from decay can become fossils. Generally only the hard parts of organisms, such as wood, bones, shells, and teeth, become fossils. In rare cases, an entire organism may be preserved. In some types of fossils, only a replica of the original organism remains. Others merely provide evidence that life once existed.

50 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Fossilization Mummification Mummified remains are often found in very dry places, because most bacteria which cause decay cannot survive in these places. Some ancient civilizations mummified their daed by carefully extracting the body’s internal organs and then wrapping the body in carefully prepared strips of cloth.

51 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Fossilization Amber Hardened tree sap is called amber. Insects become trapped in the sticky sap and are preserved when the sap hardens. In many cases, delicate features such as legs and antennae have been preserved. In rare cases, DNA has been recovered from amber.

52 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Fossilization Tar Seeps When thick petroleum oozes to Earth’s surface, the petroleum forms a tar seep. Tar seeps are commonly covered by water. Animals that come to drink the water can become trapped in the sticky tar. The remains of the trapped animals are covered by the tar and preserved.

53 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Fossilization Freezing The low temperatures of frozen soil and ice can protect and preserve organisms. Because most bacteria cannot survive freezing temperatures, organisms that are buried in frozen soil or ice do not decay.

54 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Fossilization Petrification Mineral solutions such as groundwater replace the original organic materials that were covered by layers of sediment with new materials. Some common petrifying minerals are silica, calcite, and pyrite. The substitution of minerals for organic material other results in the formation of a nearly perfect mineral replica of the original organism.

55 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Types of Fossils trace fossil a fossilized mark that formed in sedimentary rock by the movement of an animal on or within soft sediment In some cases, no part of the original organism survives in fossil form. But the fossilized evidence of past animal movement can still provide information about prehistoric life. A trace fossils in an important clue to the animal’s appearance and activities.

56 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Reading Check What is a trace fossil?

57 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Reading Check What is a trace fossil? A trace fossil is a fossilized evidence of past animal movement, such as tracks, footprints, borings, or burrows, that can provide information about prehistoric life.

58 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Types of Fossils Imprints Carbonized imprints of leaves, stems, flowers, and fish made in soft mud or clay have been found preserved in sedimentary rock. When original organic material partially decays, it leaves behind a carbon-rich film. An imprint displays the surface features of the organism.

59 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Types of Fossils Molds and Casts Shells often leave empty cavities called molds within hardened sediment. When a shell is buried, its remains eventually decay and leave an empty space. When sand or mud fills a mold and hardens, a natural cast forms. A cast is a replica of the original organism.

60 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Types of Fossils Coprolites Fossilized dung or waste materials from ancient animals are called coprolites. They can be cut into thin sections and observed through a microscope. The materials identified in these sections reveal the feeding habits of ancient animals, such as dinosaurs.

61 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Types of Fossils Gastroliths Some dinosaurs had stones in their digestive systems to help grind their food. In many cases, these stones, which are called gastroliths, survives as fossils. Gastroliths can often be recognized by their smooth, polished surfaces and by their close proximity to dinosaurs remains.

62 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Index Fossils Index fossils Index fossil a fossil that is used to establish the age of rock layers because it is distinct, abundant, and widespread and existed for only a short span of geologic time. Paleontologists can use index fossils to determine the relative ages of the rock layers in which the fossils are located.

63 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Index Fossils Index fossils To be an index fossil, a fossil must be present in rocks scattered over a large region, and it must have features that clearly distinguish it from other fossils. In addition, organisms from which the fossil formed must have lived during a short span of geologic time, and the fossil must occur in fairly large numbers within the rock layers.

64 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 The Fossil Record Chapter 8 Index Fossils and Absolute Age Scientists can use index fossils to estimate absolute ages of specific rock layers. Because organisms that formed index fossils lived during short spans of geologic time, the rock layer in which an index fossil was discovered can be dated accurately. Scientists can also use index fossils to date rock layers in separate area. Index fossils are used to help locate rock layers that are likely to contain oil and natural gas deposits.

65 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Index Fossils Section 3 The Fossil Record

66 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Maps in Action Chapter 8 Maps in Action Geologic Map of Bedrock in Ohio

67 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Brain Food Video Quiz The Rock Record

68 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice 1.A scientist used radiometric dating during an investigation. The scientist used this method because he or she wanted to determine the A. relative age of rocks. B. absolute age of rocks. C. climate of a past era. D. fossil types in a rock. Standardized Test Prep Chapter 8

69 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 1.A scientist used radiometric dating during an investigation. The scientist used this method because he or she wanted to determine the A. relative age of rocks. B. absolute age of rocks. C. climate of a past era. D. fossil types in a rock. Standardized Test Prep Chapter 8

70 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 2. Fossils that provide direct evidence of the feeding habits of ancient animals are known as F. coprolites G. molds and casts H. imprints I. trace fossils Standardized Test Prep Chapter 8

71 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 2. Fossils that provide direct evidence of the feeding habits of ancient animals are known as F. coprolites G. molds and casts H.imprints I. trace fossils Standardized Test Prep Chapter 8

72 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 3. One way to estimate the absolute age of rock is A. nonconformity B. varve count C. the law of superposition D. the law of crosscutting relationships Standardized Test Prep Chapter 8

73 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 3. One way to estimate the absolute age of rock is A. nonconformity B. varve count C. the law of superposition D. the law of crosscutting relationships Standardized Test Prep Chapter 8

74 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 4. To be an index fossil, a fossil must F. be present in rocks that are scattered over a small geographic area G. contain remains of organisms that lived for a long period of geologic time H. occur in small numbers within the rock layers I. have features that clearly distinguish it from other fossils Standardized Test Prep Chapter 8

75 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 4. To be an index fossil, a fossil must F. be present in rocks that are scattered over a small geographic area G. contain remains of organisms that lived for a long period of geologic time H. occur in small numbers within the rock layers I. have features that clearly distinguish it from other fossils Standardized Test Prep Chapter 8

76 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 5. Which of the following statements best describes the relationship between the law of superposition and the principle of original horizontality? A. Both describe the deposition of sediments in horizontal layers. B. Both conclude that Earth is more than 100,000 years old. C. Both indicate the absolute age of layers of rock. D. Both recognize that the geologic processes in the past are the same as those at work now. Standardized Test Prep Chapter 8

77 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Multiple Choice, continued 5. Which of the following statements best describes the relationship between the law of superposition and the principle of original horizontality? A. Both describe the deposition of sediments in horizontal layers. B. Both conclude that Earth is more than 100,000 years old. C. Both indicate the absolute age of layers of rock. D. Both recognize that the geologic processes in the past are the same as those at work now. Standardized Test Prep Chapter 8

78 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Short Response 6. What is the name for a type of fossil that can be used to establish the age of rock? Standardized Test Prep Chapter 8

79 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Short Response 6.What is the name for a type of fossil that can be used to establish the age of rock? Index fossil Standardized Test Prep Chapter 8

80 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills Read the passage below. Then, answer questions 7–10. Illinois Nodules Around three hundred million years ago, the region that is now Illinois had a very different climate. Swamps and marshes covered much of the area. Scientists estimate that no fewer than 500 species lived in this ancient environment. Today, the remains of these organisms are found preserved within structures known as nodules. Nodules are round or oblong structures that are usually composed of cemented sediments. Sometimes, these nodules contain the fossilized hard parts of plants and animals. The Illinois nodules are extremely rare because many contain finely detailed impressions of the soft parts of the organisms together with the hard parts. Because they are rare, these nodules are desired for their incredible scientific value and may be found in fossil collections around the world. Standardized Test Prep Chapter 8

81 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 7. According to the passage above, which of the following statements about nodules is correct? A. Nodules are rarely around or oblong. B. Nodules are usually composed of cemented sediments. C. Nodules are rarely found outside of Illinois. D. Nodules will always contain fossils. Standardized Test Prep Chapter 8

82 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 7. According to the passage above, which of the following statements about nodules is correct? A. Nodules are rarely around or oblong. B. Nodules are usually composed of cemented sediments. C. Nodules are rarely found outside of Illinois. D. Nodules will always contain fossils. Standardized Test Prep Chapter 8

83 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 8. What is the most unusual feature of the nodules found in modern-day Illinois? F. their bright coloration G. the fact that they come in many more unusual shapes than other nodules H. the fact that they contain both the soft and hard parts of animals I. their extremely heavy weight Standardized Test Prep Chapter 8

84 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 8. What is the most unusual feature of the nodules found in modern-day Illinois? F. their bright coloration G. the fact that they come in many more unusual shapes than other nodules H. the fact that they contain both the soft and hard parts of animals I. their extremely heavy weight Standardized Test Prep Chapter 8

85 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 9. Which of the following statements can be inferred from the information in the passage? A.Illinois nodules are sought by scientists. B.Nodules can be purchased from the state. C.Similar nodules can be found in nearby Iowa. D.Nodules contain dinosaur fossils. Standardized Test Prep Chapter 8

86 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 9. Which of the following statements can be inferred from the information in the passage? A.Illinois nodules are sought by scientists. B.Nodules can be purchased from the state. C.Similar nodules can be found in nearby Iowa. D.Nodules contain dinosaur fossils. Standardized Test Prep Chapter 8

87 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 10. What might scientists learn from nodules that contain the soft and hard parts of an animal? Standardized Test Prep Chapter 8

88 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued Your answer should include the following points: Fossils that include the soft parts of animals are rare and may include impressions of organs or muscles; scientists can use these animal parts to learn more about the internal structures and body systems of ancient animals; scientists can compare the internal systems of ancient animals to the internal systems of modern animals in order to see how different animals and body systems have changed over time. Standardized Test Prep Chapter What might scientists learn from nodules that contain the soft and hard parts of an animal?

89 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics Use the figure below to answer question 11. The graph shows the rate of radioactive decay. Standardized Test Prep Chapter 8

90 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued 11. How many half-lives have passed when the number of daughter atoms is approximately three times the number of parent atoms? A. one B. two C. three D. four a waning moon. Standardized Test Prep Chapter 8

91 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued 11. How many half-lives have passed when the number of daughter atoms is approximately three times the number of parent atoms? A. one B. two C. three D. four a waning moon. Standardized Test Prep Chapter 8

92 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued The diagram below shows crosscutting taking place in layers of rock. Use this diagram to answers questions 12 and 13. Standardized Test Prep Chapter 8

93 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued 12. Which of the letter combinations below belong to the same layer of rock before the fault disrupted the layer? A. C and D B. C and F C. G and I D. G and F Standardized Test Prep Chapter 8

94 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued 12. Which of the letter combinations below belong to the same layer of rock before the fault disrupted the layer? A. C and D B. C and F C. G and I D. G and F Standardized Test Prep Chapter 8

95 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued 13. Which is older, structure B or structure X? Explain your answer. What structure shown on the diagram is the youngest? Standardized Test Prep Chapter 8

96 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued Your answer should include the following points: Structure X is a simple fault, which by definition is younger than the rock it cuts through; rock layer B must have formed before fault X occurred; rock layer A is the youngest structure shown on the diagram. The unbroken layer on top is the youngest structure shown in the diagram. This layer must have formed after the fault, it would be broken in the same way that the other rock layers were broken. Standardized Test Prep Chapter Which is older, structure B or structure X? Explain your answer. What structure shown on the diagram is the youngest?

97 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Superposition Chapter 8

98 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Types of Unconformities Chapter 8

99 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Crosscutting Relationships Chapter 8

100 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Radioactive Decay and Half-Life Chapter 8

101 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Geologic Map of Bedrock in Ohio Chapter 8


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