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Name ______________________________ Class ___________________ Date __________________ Worksheet Directed Reading A Section: Evidence of the Past _____ 1. What type of scientists use fossils to reconstruct the history of life before humans existed? a. fossilologists c. sedimentologists b. dinosaurologists d. paleontologists 2. What do fossils show us? _______________________________________________________________ _______________________________________________________________ FOSSILS 3. What are fossils? _______________________________________________________________ _______________________________________________________________ Put the three stages of a fossil’s formation in order from first to last. Write the appropriate numbers from 1 to 3 on the lines provided. _____ 4. Over time, the mold fills with sediment, which forms a cast of the organism. _____ 5. The organism gradually decomposes and leaves a hollow impression, or mold, in the sediment. _____ 6. When an organism dies it becomes buried in sediment. THE AGE OF FOSSILS 7. When scientists look at which layer of rock a fossil is in they are using the ______________________ method of estimating the age of rocks and fossils. 8. When a scientist finds sedimentary rock, where are the oldest layers usually found? Why? ____________________________________________________________________ ____________________________________________________________________ 9. Scientists can determine the age of a fossil more precisely than relative dating using a method called ______________________. Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 1 The History of Life on Earth Name ______________________________ Class ___________________ Date __________________ Directed Reading A continued 10. The particles that make up all matter are called ______________________. 11. As atoms decay what do they release? _______________________________________________________________ 12. The time it takes for half of the unstable atoms in a sample to decay is the sample’s ______________________. 13. When scientists measure the ratio of unstable atoms to stable atoms in a sample of rock, what are they trying to determine? ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ THE GEOLOGIC TIME SCALE 14. Why is the earth’s history divided into very long units of time? _______________________________________________________________ _______________________________________________________________ 15. The calendar scientists use to outline the history of life on earth is called the ______________________ time scale. 16. After paleontologists have dated a fossil, how do they use the time scale to help them understand how organisms have changed over time? _______________________________________________________________ _______________________________________________________________ 17. Paleontologists have divided the geologic time scale into blocks of time. The largest divisions are known as ______________________. 18. Why is the Mesozoic era is referred to as the Age of Reptiles? _______________________________________________________________ _______________________________________________________________ 19. Does the geologic time scale change? Explain why or why not? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 2 The History of Life on Earth Name ______________________________ Class ___________________ Date __________________ Directed Reading A continued 20. When a species dies out completely we say it has become ______________________. 21. The periods when many species suddenly become extinct are called ______________________. 22. What are two of the events scientists think could have caused the extinction of the dinosaurs? _______________________________________________________________ _______________________________________________________________ THE CHANGING EARTH _____ 23. Fossils provide evidence that Antarctica was once located a. at the North Pole. c. at the South Pole. b. near the equator. d. where it is now. _____ 24. The continents may once have formed one landmass called Pangaea which means a. all seas. c. all Earth. b. puzzle. d. landmass. _____ 25. J. Tuzo Wilson’s theory of how huge pieces of Earth’s crust are pushed around by forces within the planet is called a. continents. c. plate tectonics. b. crust tectonics. d. Pangaea. _____ 26. According to the theory of plate tectonics, how many large rigid plates are there? a. five c. eight b. two d. seven 27. How do slow changes, such as moving continents, affect organisms differently than rapid changes, such as a meteorite impact, affect organisms? _______________________________________________________________ _______________________________________________________________ 28. Why are fossils found in some places very different from the organisms now living in the same area? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 3 The History of Life on Earth