The Geologic Time Scale (pp. 286 297) This section tells why the geologic time scale is used to show Earth s history, and what the organisms were like and the major events that happened in the different periods and eras. Use Target Reading Skills As you read, create an outline to show the relationships between main ideas and supporting ideas. Use the headings, subheadings, and Key Concepts to help you complete the outline. The Geologic Time Scale I. The Geologic Time Scale II. The Paleozoic Era G. H. I. III. The Mesozoic Era IV. The Cenozoic Era 148
The Geologic Time Scale (pp. 286 287) 1. Is the following sentence true or false? Using months, years, and centuries is a very useful way of thinking about Earth s long history. 2. What is the geologic time scale? 3. Geologic time begins with a long span of time called. 4. The basic units of the geologic time scale are a. and b.. Early Earth (p. 288) 5. Scientists hypothesize that all forms of life on Earth arose from that formed about. 6. How do scientists believe the ozone layer formed, and what did the ozone layer allow for? 149
The Geologic Time Scale (continued) The Paleozoic Era (pp. 289 293) 7. What happened during the Cambrian Explosion? 8. Complete the flowchart to show how living things evolved during the Paleozoic Era. The Paleozoic Era During the Silurian Period, simple a. began to grow on land in damp areas. During the Devonian Period, b. that live part of their life on land and part of their life in water, evolved., animals During the Carboniferous Period, c., which have scaly skin and lay eggs with tough, leathery shells, first developed. At the end of the Paleozoic Era, d. occurred, which means that many types of living things died out at the same time. 150
9. Is the following sentence true or false? During the Cambrian Period, all animals lived in the sea. 10. An animal with a backbone is called a(n). 11. What were the first vertebrates to evolve? 12. What is a mass extinction? 13. What is one theory for the mass extinction at the end of the Paleozoic Era? 14. What happened to Earth s continents during the Permian Period? 151
The Geologic Time Scale (continued) 15. Is the following sentence true or false? The formation of Pangaea caused the climate on Earth to change. The Mesozoic Era (pp. 294 295) 16. Circle the letter of the type of living thing that was most successful during the Mesozoic Era. a. insects b. fish c. conifers d. reptiles 17., the first warm-blooded vertebrates that fed their young with milk, appeared during the Triassic Period. 18. One of the first birds appeared in the Period of the Mesozoic Era. 19. Circle the letter of each sentence that is true about living things in the Cretaceous Period. a. Reptiles were the dominant vetebrates. b. Flying reptiles were better adapted to flying than birds. c. Turtles and crocodiles became extinct. d. Flowering plants evolved. 20. What is one hypothesis for the mass extinction at the end of the Cretaceous Period? The Cenozoic Era (pp. 296 297) 21. Why didn t mammals evolve more during the Mesozoic Era? _ 22. Is the following sentence true or false? Whales are mammals that evolved in the oceans during the Tertiary Period. 23. How did Earth s climate change in the Quaternary Period? _ 24. Modern humans may have appeared in the Period. 152