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2. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Visual Concepts Image and Math Focus Bank

3. The Rock and Fossil Record Chapter F3 Table of Contents Section 1 Earth’s Story and Those Who First Listened Section 2 Relative Dating: Which Came First? Section 3 Absolute Dating: A Measure of Time Section 4 Looking at Fossils Section 5 Time Marches On

4. Chapter F3 Section1 Earth’s Story and Those Who First Listened Bellringer “The Present Is the Key to the Past.”This phrase was the cornerstone of the uniformitarianist theory developed by geologist James Hutton in the late 1700s. Write a few sentences in your science journalabout how studying the present could reveal the story of Earth’s history. Use sketches to illustrate processes that occurred millions of years ago that you can still see today.

5. Chapter F3 Section1 Earth’s Story and Those Who First Listened Objectives • Compare uniformitarianism and catastrophism. • Describe how the science of geology has changed over the past 200 years. • Explain the role of paleontology in the study of Earth’s history.

6. Chapter F3 Section1 Earth’s Story and Those Who First Listened The Principle of Uniformitarianism • Scientist James Hutton, the author of Theory of the Earth, proposed that geologic processes such as erosion and deposition do not change over time. • Uniformitarianism is the idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history. • The next slide shows how Hutton developed the idea of uniformitarianism.

7. Chapter F3 Section1 Earth’s Story and Those Who First Listened

8. Chapter F3 Section1 Earth’s Story and Those Who First Listened The Principle of Uniformitarianism, continued • Uniformitarianism Versus Catastrophism Hutton’s theories sparked a scientific debate by suggesting the Earth was much older than a few thousand years, as previously thought. • A few thousand years was not enough time for the gradual geologic processes that Hutton described to have shaped the planet.

9. Chapter F3 Section1 Earth’s Story and Those Who First Listened The Principle of Uniformitarianism, continued • A Victory for Uniformitarianism Catastrophism was geology’s guiding principle until the work of geologist Charles Lyell caused people to reconsider uniformitarianism. • Lyell published Principles of Geology in the early 1830s. Armed with Hutton’s notes and new evidence of his own, Lyell successfully challenged the principle of catastrophism.

10. Chapter F3 Section1 Earth’s Story and Those Who First Listened Modern Geology -- A Happy Medium • During the late 20th century, scientists such as Stephen J. Gould challenged Lyell’s uniformitarianism. They believed that catastrophes occasionally play an important role in shaping Earth’s history. • Today, scientists realize that most geologic change is gradual and uniform, but catastrophes that cause geologic change have occurred during Earth’s long history.

11. Chapter F3 Section1 Earth’s Story and Those Who First Listened Uniformitarianism and Catastrophism Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

12. Chapter F3 Section1 Earth’s Story and Those Who First Listened Paleontology -- The Study of Past Life • The history of the Earth would be incomplete without knowledge of the organisms that have inhabited our planet and the conditions under which they lived. • The science involved with the study of past life is called paleontology. • Paleontologist study fossils, which are the remains of organisms preserved by geologic processes.

13. Section2 Relative Dating: Which Came First? Chapter F3 Bellringer Arrange the following sentences in a logical order to make a short story: I stood in the checkout line. I selected two apples. I walked home from the store. I gave the cashier money. I went to the store. The cashier gave me change. I was hungry. Write your story in your science journal.

14. Section2 Relative Dating: Which Came First? Chapter F3 Objectives • Explain how relative dating is used in geology. • Explain the principle of superposition. • Describe how the geologic column is used in relative dating. • Identify two events and two features that disrupt rock layers. • Explain how physical features are used to determine relative ages.

15. Section2 Relative Dating: Which Came First? Chapter F3 The Principle of Superposition • Geologists try to determine the order in which events have happened during Earth’s history. They rely on rocks and fossils to help them in their investigation. • The process of determining whether an event or object is older or younger than other events or objects is called relative dating.

16. Section2 Relative Dating: Which Came First? Chapter F3 The Principle of Superposition, continued • Layers of sedimentary rock, such as the ones shown below, are stacked like pancakes.

17. Section2 Relative Dating: Which Came First? Chapter F3 The Principle of Superposition, continued • As you move from the top to the bottom in layers of sedimentary rock, the lower layers are older. • Superposition is a principle that states that younger rocks lie above older rocks, if the layers have not been disturbed.

18. Section2 Relative Dating: Which Came First? Chapter F3 The Principle of Superposition, continued • Disturbing Forces Not all rock sequences are arranged with the oldest layers on the bottom and the youngest layers on top. • Some rock sequences have been disturbed by forces within the Earth. • These forces can push other rocks into a sequence, tilt or fold rock layers, and break sequences into moveable parts.

19. Section2 Relative Dating: Which Came First? Chapter F3 The Geologic Column • The geologic column is an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth, arranged from oldest to youngest. • Geologists use the geologic column to interpret rock sequences and to identify the layers in puzzling rock sequences.

20. Section2 Relative Dating: Which Came First? Chapter F3 Geologic Column Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

21. Section2 Relative Dating: Which Came First? Chapter F3 Disturbed Rock Layers • Geologists often find features that cut across existing layers of rock. • Geologists use the relationships between rock layers and the features that cross them to assign relative ages to the features and the layers. • The features must be younger than the rock layers because the rock layers had to be present before the features could cut across them.

22. Section2 Relative Dating: Which Came First? Chapter F3 Disturbed Rock Layers, continued • Events That Disturb Rock Layers Geologists assume that the way sediment is deposited to form rock layers — in horizontal layers — has not changed over time. • If rock layers are not horizontal, something must have disturbed them after they formed. • The next slide describes four ways that rock layers may become disturbed.

23. Section2 Relative Dating: Which Came First? Chapter F3 Disturbed Rock Layers, continued • A fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another. • An intrusion is molten rock from the Earth’s interior that squeezes into existing rock and cools. • Folding occurs when rock layers bend and buckle from Earth’s internal forces. • Tilting occurs when internal forces in the Earth slant rock layers.

24. Section2 Relative Dating: Which Came First? Chapter F3 Gaps in the Record -- Unconformities • Missing Evidence Sometimes, layers of rock are missing, creating a gap in the geologic record. Missing rock layers create breaks in rock-layer sequences called unconformities. • An unconformity is a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

25. Section2 Relative Dating: Which Came First? Chapter F3 Unconformities Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

26. Section2 Relative Dating: Which Came First? Chapter F3 Types of Unconformities • Most unconformities form by both erosion and nondeposition, but other factors may be involved. • To simplify the study of unconformities, geologists place them into three major categories: disconformities, nonconformities, and angular unconformities.

27. Section2 Relative Dating: Which Came First? Chapter F3 Types of Unconformities, continued • Disconformities exist where part of a sequence of parallel rock layers is missing.

28. Section2 Relative Dating: Which Came First? Chapter F3 Types of Unconformities, continued • Nonconformities exist where sedimentary rock layers lie on top of an eroded surface of nonlayered igneous or metamorphic rock.

29. Section2 Relative Dating: Which Came First? Chapter F3 Types of Unconformities, continued • Angular Unconformities exist between horizontal rock layers and rock layers that are tilted or folded.

30. Section2 Relative Dating: Which Came First? Chapter F3 Rock-Layer Puzzles • Rock-layer sequences often have been affected by more than one geological event or feature. • For example, intrusions may squeeze into rock layers that contain an unconformity, as shown at right.

31. Section2 Relative Dating: Which Came First? Chapter F3 Rock-Layer Puzzles, continued • Determining the order events that led to a sequence that has been disturbed by more than one rock-disturbing feature is like solving a jigsaw puzzle. • Geologists must use their knowledge of the events that disturb rock-layer sequences to piece together the history of the Earth.

32. Section3 Absolute Dating: A Measure of Time Chapter F3 Bellringer Do the following statements describe relative or absolute age? 1. She is my younger sister. 2. He is 12 years old. Why do geologists use both absolute and relative dating to interpret the past? Why are both absolute and relative dates valid dates for geologists, and other earth scientists to use? Write a paragraph in your science journal.

33. Section3 Absolute Dating: A Measure of Time Chapter F3 Objectives • Describe how radioactive decay occurs. • Explain how radioactive decay relates to radiometric dating. • Identify four types of radiometric dating. • Determine the best type of radiometric dating to use to date an object.

34. Section3 Absolute Dating: A Measure of Time Chapter F3 Radioactive Decay • Absolute dating is any method of measuring the age of an event or object in years. • To determine the absolute ages of fossils and rocks, scientists analyze isotopes of radioactive elements. • Atoms of the same element that have the same number of protons but different numbers of neutrons are called isotopes.

35. Section3 Absolute Dating: A Measure of Time Chapter F3 Radioactive Decay, continued • Most isotopes are stable, meaning that they stay in their original form. • Other isotopes are unstable. Scientists call unstable isotopes radioactive.

36. Section3 Absolute Dating: A Measure of Time Chapter F3 Radioactive Decay, continued • Radioactive isotopes tend to break down into stable isotopes of the same or other elements in a process called radioactive decay.

37. Section3 Absolute Dating: A Measure of Time Chapter F3 Radioactive Decay, continued • Because radioactive decay occurs at a steady rate, scientists can use the relative amounts of stable and unstable isotopes present in an object to determine the object’s age.

38. Section3 Absolute Dating: A Measure of Time Chapter F3 Radioactive Decay, continued • Dating Rocks — How Does It Work? In radioactive decay, an unstable radioactive isotope of one element breaks down into a stable isotope. The stable isotope may be of the same element or of a different element. • The unstable radioactive isotope is called the parent isotope. • The stable isotope produced by the radioactive decay of the parent isotope is called the daughter isotope.

39. Section3 Absolute Dating: A Measure of Time Chapter F3 Radioactive Decay, continued • The rate of radioactive decay is constant, so scientists can compare the amount of parent material with the amount of daughter material to date rock. • The more daughter material there is, the older the rock is.

40. Section3 Absolute Dating: A Measure of Time Chapter F3 Radiometric Dating • Determining the absolute age of a sample, based on the ratio of parent material to daughter material is called radiometric dating. • If you know the rate of decay for a radioactive element in a rock, you can figure out the absolute age of the rock.

41. Section3 Absolute Dating: A Measure of Time Chapter F3 Radiometric Dating, continued • A half-life is the time needed for half of a sample of a radioactive substance to undergo radioactive decay. • After every half-life, the amount of parent material decrease by one-half.

42. Section3 Absolute Dating: A Measure of Time Chapter F3 Types of Radiometric Dating • Scientists use different radiometric-dating methods based on the estimated age of an object. There are four radiometric-dating techniques. • Potassium-Argon Method Potassium-40 has a half-life of 1.3 billion years, and it decays leaving a daughter material of argon. • This method is used mainly to date rocks older than 100,000 years.

43. Section3 Absolute Dating: A Measure of Time Chapter F3 Types of Radiometric Dating, continued • Uranium-Lead Method Uranium-238 is a radioactive isotope with a half-life of 4.5 billion years. Uranium-238 decays in a series of steps to lead-206. • The uranium-lead method can be used to date rocks more than 10 million years old.

44. Section3 Absolute Dating: A Measure of Time Chapter F3 Types of Radiometric Dating, continued • Rubidium-Strontium Method The unstable parent isotope rubidium-87 forms a stable daughter isotope strontium-87. • The half-life of rubidium-87 is 49 billion years. This method is used for rocks older than 10 million years.

45. Section3 Absolute Dating: A Measure of Time Chapter F3 Types of Radiometric Dating, continued • Carbon-14 Method Carbon is normally found in three forms, the stable isotopes carbon-12 and carbon-13, and the radioactive isotope carbon-14. • Living plants and animals contain a constant ratio of carbon-14 to carbon-12. Once a plant or animal dies, no new carbon is taken in. The amount of carbon-14 begins to decrease as the plant or animal decays.

46. Section3 Absolute Dating: A Measure of Time Chapter F3 Types of Radiometric Dating, continued • The half-life of carbon-14 is 5,730 years. • The carbon-14 method of radiometric dating is used mainly for dating things that lived within the last 50,000 years.

47. Section3 Absolute Dating: A Measure of Time Chapter F3 Radiometric Dating Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

48. Section4 Looking at Fossils Chapter F3 Bellringer Describe the fossil record of your own life that might be found 65 million years from now. What items, or artifacts, might be likely to survive? What kinds of things would decay and disappear? Do you think your fossil record would produce an accurate picture of your life? What might be missing? Write your description in your science journal.

49. Section4 Looking at Fossils Chapter F3 Objectives • Describe five ways that different types of fossils form. • List three types of fossils that are not part of organisms. • Explain how fossils can be used to determine the history of changes in environments and organisms. • Explain how index fossils can be used to date rock layers.

50. Section4 Looking at Fossils Chapter F3 Fossilized Organisms • The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock is called a fossil. • Fossils are most often preserved in sedimentary rock, but other materials can also preserve evidence of past life.