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A View of Earth’s Past TEACHING TRANSPARENCY Precambrian Time and the Paleozoic Era Cenozoic Era Mesozoic Era Paleozoic Era present 4,600 Ma Precambrian time (4,600 Ma to 542 Ma) First crustal rocks form. First fungi appear. First known unicellular life appears. Earth's surface is cool enough for liquid water. Earth's atmosphere starts to become oxygen rich. First shelled organisms, such as arthropods and mollusks, appear. First known multicellular life appears. The Paleozoic Era Paleozoic Era (542 Ma to 251 Ma) Precambrian time Cambrian Period Ordovician Period First possible vertebrates appear. Silurian Period First land plants appear. Modern, oxygen-rich atmosphere has formed. Devonian Period Mesozoic Era Carboniferous Period First amphibians appear. First arthropods appear on land. First reptiles appear. Permian Period Formation of Pangaea is complete. Permian mass extinction results from major environmental changes. Copyright © by Holt, Rinehart and Winston. All rights reserved. Precambrian Time 46 Name Class Date Transparency Worksheet Precambrian Time and the Paleozoic Era 1. What occurred that enabled the first life-forms to evolve on Earth? 2. During which geologic time period did single-celled life appear? 3. The formation of the single landmass, Pangaea, occurred just prior to what period? 4. For what reason did geologists divide the Paleozoic Era into seven periods? 5. Which were the most common invertebrates during the Cambrian Period? 6. List two events that occurred during the Silurian Period. 7. During which geologic period did the first amphibians appear? Copyright © by Holt, Rinehart and Winston. All rights reserved. Holt Earth Science A View of Earth’s Past ANSWER KEY 2. 3. 4. 5. 48 Fossil Evidence for Gondwanaland are closer to the surface, so studying the fossils in younger rocks is easier. 488 million years ago about 63.7 million years Precambrian time is the longest geologic time span in Earth’s history. It is poorly represented because very few fossils exist from the unit of geologic time. Forests and swamps that contributed vegetation to the deposists covered large areas. 1. South America, Africa, Australia, Asia (India), and Antarctica 2. Africa, Asia, and Antarctica 3. Mesosaurus 4. South America, Antarctica, Asia (India), and Australia were likely touching Africa. 5. Africa, Australia, and Asia, (India), were likely touching Antarctica 6. Answers may vary. sample answer: The organisms did not appear in other parts of the world and were not part of the Gondwanaland part of Pangaea. 7. Answers amy vary. Students may state that because the trend has been for the continents to separate, they would likely continue to move farther apart. 45 Similar Skeletal Structures of Mammals 1. that any mammal species has five dig- its on each limb 2. their different means of locomotion 3. The bat’s “wrist” joint is most prominent. The cat’s “elbow” joint is most prominent. You can tell equivalent joints by the bones that make up the joint. 4. Limb changes are most extreme in the dolphin. It is the only mammal shown that moves exclusively through water. 49 Sea-Floor Spreading 1. from magma deep inside Earth 2. Magma can arise at mid-ocean ridges because the crust is rifting at these sites. It is rifting because mid-ocean ridges are the sites where tectonic plates are pulling apart. 3. The oldest crust is farthest from the ridge. 4. The oldest crust would be closest to continents. 5. because sea-floor spreading is due to pulling apart, or movement of plates, at mid-ocean ridges 46 Precambian Time and the Paleozoic Era 1. water formed 2. Precambrian time 3. Pennsylvanian Period of the Carboniferous Period 4. because of its rich fossil record 5. tribolites 6. The first land plants appeared and the 50 Tectonic Plate Boundaries first arthropods appeared on land. 7. the Devonian Period 1. 15 2. both continental crust and oceanic crust 47 The Mesozoic and Cenozoic Eras 3. the region where the Nazca plate and 1. 2. 3. 4. about 70 million years the breakup of Pangaea the Tertiary Period It drifted to the South Pole during this epoch; therefore, it most likely was warmer than it is today. 5. Modern humans first appeared in the Holocene Epoch and have been on Earth less than 115,000 years. 6. The Mesozoic Era was longer by 120 million years. The Mesozoic Era lasted 185.5 million years (251 Ma – 65.5 Ma = 185.5 Ma); the Cenozoic Era lasted 65.5 million years (65.5 Ma – 0 Ma = 65.5 Ma; 185.5 Ma – 65.5 Ma = 120 Ma). the Pacific plate meet in the southern Pacific 4. Students should indicate the path of the mid-ocean ridges that follow the lines delineating the tectonic plates around the globe. They should recognize that the metaphor is a good one to describe the way the mid-ocean mountain chains ring the planet. 5. the North American plate and the Pacific plate 51 Types of Plate Boundaries 1. divergent plate boundary Copyright © by Holt, Rinehart and Winston. All rights reserved. Holt Earth Science 13 Answer Key