Chapter 17 Questions Chapter 17.1 1. What does the fossil record show us? 2. What portion of all species that have lived on earth have become extinct? 3. Why is the fossil record described as an incomplete record of life’s history? 4. What two factors allow a fossil to be considered an index fossil? 5. How do scientists use index fossils? 6. What method of geologic dating do scientists use to determine the absolute age of rock? 7. What radioactive isotope is best used for fossils that are very young (60,000 years or so)? 8. What radioactive isotope is best used for fossils that are very old( millions of years) ? 9. Looking at Figure 17.4 after how many years will only 1/8th of the original sample remain? 10. About _____________ percent of the Earths history is covered in the Precambrian time? 11. What is the Mesozoic era often referred to as? 12. What period existed 500million years ago? 13. How long did the Triassic period last? 14. What is the most recent era? 15. Notice that the time at which one period ends is the exact time another begins!!!! Chapter 17.2 1. Geologic evidence shows that earth is approximately how old? 2. Why did earth not have oceans at first? 3. What did Miller and Ureys experiment suggest about earth? 4. What did they fill the flask with and why? 5. What is the purpose of the electrodes in the experimental set-up? What do they electrodes represent? 6. Under certain conditions large organic molecules can from tiny bubbles called what? 7. ___________ are not ____________ but have some characteristics of living things? 8. What type of organisms where prevalent in the seas during the Precambrian? 9. What process added oxygen to the Earths atmosphere? 10. What did the oxygen combine with and what did it cause that we use today? 11. When oxygen levels rose in the atmosphere/oceans what happened to the existing organisms (2 things)? 12. Where the first organisms on earth prokaryotic or eukaryotic? 13. What is the endo-symbiotic theory? 14. What are the characteristics of Mitochondria and Chloroplasts that support the endosymbiotic hypothesis? Chapter 17.3 1. The fossil record indicates that that major changes occurred in earths 2. Why are there so few fossils from the Precambrian time? 3. Where did life exist during the early Paleozoic Era? 4. The diversification of life during early Cambrian was also known as…. 5. What is a vertebrate? 6. Where did the first land plants come from? 7. What evolutionary milestone occurred during the Denovian Period? 8. What is a mass extinction? 9. What percent of life disappeared at the end of the Paleozoic? 10. What evidence links dinosaurs and birds as relatives? 11. What major event enabled mammals to become the dominant animals? 12. The fossil records suggests that ancestors to humans first appeared___________?