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Table of Contents Chapter Preview 8.1 The Rock Cycle 8.2 The Relative Age of Rocks 8.3 Radioactive Dating 8.4 Movement of Earths Plates 8.5 The Geological Time Scale

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Chapter 8 Preview Questions 1. The laying down of sediment is a. weathering. b. erosion. c. creep. d. deposition.

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Chapter 8 Preview Questions 1. The laying down of sediment is a. weathering. b. erosion. c. creep. d. deposition.

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Chapter 8 Preview Questions 2. The movement of Earths landmasses is called a. mass movement. b. continental drift. c. deposition. d. Pangaea.

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Chapter 8 Preview Questions 2. The movement of Earths landmasses is called a. mass movement. b. continental drift. c. deposition. d. Pangaea.

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Chapter 8 Preview Questions 3. Evidence of Earths history can be found in a. fossils. b. climate change. c. land features. d. all of these.

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Chapter 8 Preview Questions 3. Evidence of Earths history can be found in a. fossils. b. climate change. c. land features. d. all of these.

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Chapter 8 Preview Questions 4. Which of the following is NOT a process in the rock cycle? a. melting b. weathering c. continental drift d. volcanic activity

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Chapter 8 Preview Questions 4. Which of the following is NOT a process in the rock cycle? a. melting b. weathering c. continental drift d. volcanic activity

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While hiking, you find a rock containing a small fossil. The fossil looks like the shell of a present-day clam. When this fossilized organism was alive, what kind of environment existed in the area where you are hiking? Explain your answer. How does evidence from rocks help scientists understand Earths history?

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Use Clues to Determine Meaning The relative age of a rock is its age compared to the ages of other rocks. You have probably used the idea of relative age when comparing your age with someone elses age, such as the age of an older brother or younger sister. The relative age of a rock does not give the exact number in years since the rock was formed. A similar example What relative age means? What the term does not mean

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Apply It! 1. In your own words, explain what relative age means. Relative age is someone or somethings age compared to the age of someone or something else. 2. What familiar example is relative age compared to? It is compared to the age of an older brother or younger sister.

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Section 8.1: The Rock Cycle The Rock Cycle What is uniformitarianism? What is the rock cycle?

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THE THREE TYPES OF ROCKS ROCKS = A MIXTURE OF MINERALS AND OTHER MATERIALS. IGNEOUS ROCKS FORM WITHIN THE EARTH AS MOLTEN MAGMA. SEDIMENTARY ROCK = FORM FROM THE WEATHERING AWAY OF OTHER ROCKS. METAMORPHIC ROCK = ROCKS THAT FORM FROM SEDIMENTARY ROCK AFTER HEAT, PRESSURE OR CHEMICALS CHANGE THEM.

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IGNEOUS ROCKS IGNEOUS ROCKS FORM WITHIN THE EARTH AS MOLTEN MAGMA.

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SEDIMENTARY ROCK SEDIMENTARY ROCK = FORM FROM THE WEATHERING AWAY OF OTHER ROCKS.

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METAMORPHIC ROCK METAMORPHIC ROCK = ROCKS THAT FORM FROM SEDIMENTARY ROCK AFTER HEAT, PRESSURE OR CHEMICALS CHANGE THEM.

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A Cycle of Many Pathways Forces deep inside Earth and at the surface produce a slow cycle that builds, destroys, and changes the rocks in the crust.

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Rocks and the Rock Cycle Rocks change continuously through the rock cycle.

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Rocks and the Rock Cycle Rocks change continuously through the rock cycle.

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Rocks and the Rock Cycle Rocks change continuously through the rock cycle.

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Rocks and the Rock Cycle Rocks change continuously through the rock cycle.

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Rocks and the Rock Cycle Rocks change continuously through the rock cycle.

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Rocks and the Rock Cycle Rocks change continuously through the rock cycle.

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Section 8.2: The Relative Age of Rocks What is the law of superposition? How do geologists determine the relative age of rocks? How are index fossils useful to geologists?

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The Position of Rock Layers GEOLOGISTS USE THE LAW OF SUPERPOSITION TO HELP DETERMINE THE AGE OF ROCKS. THE LAW STATES THAT ROCKS ON TOP OF OTHER ROCKS ARE YOUNGER. AND THAT THE OLDEST ROCKS ARE FOUND ON THE BOTTOM.

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Determining Relative Age To determine relative age, geologists also study extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.

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Determining Relative Age An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

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Determining Relative Age An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

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Determining Relative Age An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

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Determining Relative Age An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.

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Using Fossils to Date Rocks Index fossils are useful because they tell the relative ages of the rock layers in which they occur.

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FOSSILS MOST FOSSILS ARE FOUND IN SEDIMENTARY ROCK. FOSSILS PROVIDE EVIDENCE OF HOW LIFE HAS CHANGED OVER TIME. SCIENTISTS WHO STUDY FOSSILS ARE CALLED PALEONTOLOGISTS. THERE ARE VARIOUS KINDS OF FOSSILS DEPENDING ON HOW THEY FORMED.

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Section 8.3: Radioactive Dating What happens during radioactive decay? What can be learned from radioactive dating? What is the probably age of Earth?

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Radioactive Decay WHEN THE ATOMS IN ONE ELEMENT ARE UNSTABLE THEY LOSE PROTONS TO BECOME ANOTHER ELEMENT. GEOLOGISTS USE RADIOACTIVE DECAY TO DETERMINE ABSOLUTE AGES OF ROCKS. THE RATE OF RADIOACTIVE DECAY IS AN ELEMENTS HALF-LIFE.

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Radioactive Decay. POTASSIUM-ARGON DATING = POTASSIUM-40 TURNS INTO ARGON-40 IN RADIOACTIVE DECAY. THIS DATING METHOD IS USED ON THE MOST ANCIENT ROCKS. CARBON 14 TURNS INTO NITROGEN-14 AND IS VERY USEFUL FOR DATING PLANTS AND ANIMALS BECAUSE ALL PLANTS AND ANIMALS HAVE CARBON 14 IN THEM.

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Radioactive Decay The half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay.

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Determining Absolute Ages Geologists use radioactive dating to determine the absolute ages of rocks.

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Percentages What percentage of a radioactive element will be left after three half-lives? First multiply 1/2 three times to determine what fraction of the element will remain. You can convert this fraction to a percentage by setting up a proportion: To find the value of d, begin by cross-multiplying, as for any proportion: 1 x 100 = 8 x d d = d = 12.5%

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Percentages Practice Problem What percent of a radioactive element will remain after five half-lives? 3.125%

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Section 8.4: Movement of Earths Plates How does the theory of plate tectonics explain the movement of Earths landmasses? How has the movement of Earths plates affected organisms?

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Continental Drift The theory of plate tectonics states that Earths landmasses have changed position over time because they are part of plates that are slowly moving.

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Section 8.5: The Geological Time Scale Why is the geological time scale used to show Earths history? What were early Precambrian organisms like? What were the major events of the Paleozoic, Mesozoic, and Cenozoic Eras?

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The Precambrian Earth The Precambrian Era The earth forms from dust and gas 4.6 billion years ago First Bacteria First animals to use suns energy The Paleozoic Era (ancient life) Life explodes on the scene Shelled animals form Jawless fish evolve Plants begin to grow on land At the end, animals begin to invade land Mass extinction (Pangaea)

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The Mesozoic Era (middle ages) Animals that survived the Paleozoic Era Mammals began to appear Dinosaurs began to dominate (Jurassic) The first bird Archaeopteryx Flowers evolved (Cretaceous) Another mass extinction wiped out the dinosaurs THE Cenozoic Era The age of mammals Marine mammals Man evolves (quaternary)

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The Geologic Time Scale Because the time span of Earths past is so great, geologists use the geologic time scale to show Earths history.

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Mass Extinctions The graph shows how the number of families of animals in Earths oceans has changed.

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Mass Extinctions The x-axis shows time in millions of years before the present; the y-axis shows the number of families of ocean animals. Reading Graphs: What variable is shown on the x-axis? On the y-axis of the graph?

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Mass Extinctions Slightly more than 50 million years ago Interpreting Data: How long ago did the most recent mass extinction occur?

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Mass Extinctions The one that occurred about 230 million years ago Interpreting Data: Which mass extinction produced the greatest drop in the number of families of ocean animals?

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Mass Extinctions The number of families of ocean animals immediately dropped but then increased. Relating Cause and Effect: In general, how did the number of families change between mass extinctions?

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Geologic History

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