How to Use This Presentation To View the presentation as a slideshow with effects select “View”...

How to Use This Presentation

• To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show”, or simply press F5 on the top row of your keyboard.

• To advance to the next slide click the left mouse button once.

• From the Chapter screen you can click on any section to go directly to that section’s presentation.

• Blank or “missing” areas of a slide will remain hidden until the left mouse button is clicked.

• You may exit the slide show at any time by pressing the Esc key

Copyright © by Holt, Rinehart and Winston. All rights reserved.

The Rock and Fossil RecordModule F: Chapter 3

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


End of Slide

Earth’s Story and Those Who First ListenedSection 1

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 journal about 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.



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.


End of Slide


The Principle of Uniformitarianism• What Is Uniformitarianism? Uniformitarianism is the idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history. Uniformitarianism is illustrated on the next slide.

• Uniformitarianism Verses Catastrophism Catastrophism is the principle that states that all geologic change occurs suddenly. In the past, most scientists supported catastrophism rather than uniformitarianism.

• A Victory for Uniformitarianism Geologist Charles Lyell made uniformitarianism popular in the 1830s.


End of Slide

Hutton and the Principles of UniformitarianismSection 1



Modern Geology—A Happy Medium• Best of Both Worlds Modern geology is based on the idea that gradual geologic change is interrupted by catastrophes.


• The Story Told by Fossils Using fossils to study past life is called paleontology.

Paleontology—The Study of Past Life

End of Slide

Relative Dating: Which Came First?Section 2

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.



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.


End of Slide


The Principle of Superposition


• What Is Superposition? The principle that states that younger rocks lie above older rocks in undisturbed sequences is called superposition.

• Disturbing Forces Not all rock sequences are arranged with the oldest layers on the bottom and the youngest layers on top. Some rock sequences are disturbed by forces within the Earth.

End of Slide


The Geologic Column


• What Is 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.

• Constructing the Geologic Column The next slide shows how the geologic column is constructed.

End of Slide

Constructing the Geologic ColumnSection 2



Disturbed Rock Layers


• Types of Disturbances Faults and intrusions are examples of features that cut across rock, thus disturbing the layers.

• Events That Disturb Rock Layers Folding and tilting are two types of events that disturb rock layers. These events are always younger than the rock layers they affect.

End of Slide


Gaps in the Record—Uncomformities


• Broken Record Sometimes, layers of rock are missing altogether, creating a gap in the geologic record.

• Missing Evidence Missing rock layers create breaks in rock-layer sequences called unconformities. An unconformity is a surface that represents a missing part of the geologic column.

End of Slide


Types of Uncomformities


• Discomformities Disconformities are found where part of a sequence of parallel rock layers is missing.

• Noncomformities Noncomformities are found where horizontal sedimentary rock layers lie on top of an eroded surface of older intrusive igneous or metamorphic rock.

• Angular Uncomformities Angular Uncomformities are found between horizontal layers of sedimentary rock and layers of rock that have been tilted or folded.

End of Slide


Rock Layer Puzzles


• More Than One Disturbance Geologists often find rock-layer sequences that have been affected by more than one of the events and features mentioned in this section.

• Solving the Puzzle Determining the order of events that led to such a sequence is like piecing together a jigsaw puzzle. Geologists must use their knowledge of the events that disturb or remove rock-layer sequences to help piece together the history of Earth as told by the rock

End of Slide

Absolute Dating: A Measure of TimeSection 3

Bellringer

Do these 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.



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.


End of Slide


Radioactive Decay

• What Is Radioactive Decay? Radioactive isotopes tend to break down into stable isotopes of the same or other elements in a process called radioactive decay.

• Dating Rock—How Does It Work? An 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. To date rock, scientists compare the amount of parent material with the amount of daughter material. The more daughter material there is, the older the rock is.


End of Slide


Radiometric Dating

• What Is Radiometric Dating? Determining the absolute age of a sample, based on the ratio of parent material to daughter material, is called radiometric dating.

• Rate of Decay If you know the rate of decay for a radioactive element in a rock, you can figure out the absolute age of the rock. A half-life is the time that it takes one-half of a radioactive sample to decay.


End of Slide


Types of Radiometric Dating

• Potassium-Argon Method This method is used mainly to date rocks older than 100,000 years.

• Uranium-Lead Method Uranium-lead dating can be used for rocks more than 10 million years old.

• Rubidium-Strontium Method This method is also used to date rocks older than 10 million years.

• Carbon-14 Method This dating method is used mainly for dating things that lived within the last 50,000 years.


End of Slide

Looking at FossilsSection 4

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. Later, you will share your description with the class.



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.


End of Slide


Fossilized Organisms

• Fossils in Rocks Sometimes organisms are quickly buried by sediment when they die. When the sediment becomes rock, parts of the organism’s body may be preserved.

• Fossils in Amber Hardened tree sap is called amber. Some of our best insect fossils are found in amber.

• Fossils in Asphalt There are places where asphalt wells up at the Earth’s surface in thick, sticky pools. These pools of thick, sticky asphalt have trapped and preserved many kinds of organisms


End of Slide


Fossilized Organisms continued

• Petrifaction Petrifaction is a process in which minerals replace an organism’s tissues.

• Frozen Fossils Because cold temperatures slow down decay, many types of frozen fossils are preserved from the last ice age.


End of Slide


Other Types of Fossils

• Trace Fossils Any naturally preserved evidence of animal activity is called a trace fossil. Tracks are an example of a trace fossil.

• Molds and Casts A cavity in rock where a plant or animal was buried is called a mold. A cast is an object created when sediment fills a mold and becomes rock.


End of Slide


Using Fossils to Interpret the Past

• The Information in the Fossil Record The fossil record offers only a rough sketch of the history of life on Earth. However, the fossil record is incomplete.

• History of Environmental Changes Fossils can tell scientists whether the climate in an area was cooler or wetter in an area than it is at present.

• History of Changing Organisms By studying the relationships between fossils, scientists can interpret how life has changed over time.


End of Slide


Using Fossils to Date Rocks

• Ammonites Index fossils are fossils of organisms that lived during a relatively short, well-defined geologic time span. One example of an index fossil is the fossil of a genus of ammonites called Tropites. Tropites lived between 230 million and 208 million years ago and is an index fossil for that period of time.

• Trilobites Fossils of a genus of trilobites called Phacops are another example of an index fossil. When scientists find Phacops in a rock, they assume that the rock is approximately 400 million years old.


End of Slide

Time Marches OnSection 5

Bellringer

Archaeologists and paleontologists believe that modern humans have lived on Earth for 150 to 200,000 years. If we imagine the history of Earth to be the length of one calendar year, on which date do you think modern humans arrived? Record your answer in your science journal.



Objectives

• Explain how geologic time is recorded in rock layers.

• Identify important dates on the geologic time scale.

• Explain how environmental changes resulted in the extinction of some species.


End of Slide


Geologic Time

• The Rock Record and Geologic Time One of the best places in North America to see the Earth’s history recorded in rock layers is in Grand Canyon National Park. These layers represent almost half, or nearly 2 billion years, of Earth’s history.

• The Fossil Record and Geologic Time Fossils of plants and animals are common in some rocks. These fossils contribute to our understanding of geologic time.


End of Slide


The Geologic Time Scale• Divisions of Time Geologists have divided Earth’s history into sections of time. The largest divisions of geologic time are eons. Eons are divided into eras, eras into periods, and periods into epochs.

• The Appearance and Disappearance of Species At certain times during Earth’s history, the number of species has increased or decreased dramatically. An increase or decrease in the number of species often comes as a result of either a relatively sudden increase or decrease in competition among species.


End of Slide


The Geologic Time Scale continued• The Paleozoic Era—Old Life The Paleozoic era lasted from about 543 million to 248 million years ago. It is the first era well represented by fossils.

• The Mesozoic Era—The Age of Reptiles The Mesozoic era began about 248 million years ago. The Mesozoic is known as the Age of Reptiles because reptiles, such as dinosaurs, inhabited the land.

• The Cenozoic Era—The Age of Mammals The Cenozoic era began about 65 million years ago and continues to the present.


End of Slide

The Geologic Time ScaleSection 5


Plate TectonicsChapter 7

Concept Map


Use the following terms to complete the concept map on the next slide: sedimentary rocks, radioactive isotope, fossils, absolute date, half-life, faults.

Concept MapChapter 6


How to Use This Presentation To View the presentation as a slideshow with effects select “View”...

Documents

Transcript of How to Use This Presentation To View the presentation as a slideshow with effects select “View”...