Chapter 10. Geologic Time

After reading the chapter and attending all lectures and viewing the films, you should be able to:
1. distinguish between relative dating and absolute dating of geologic features.
2. describe how the relative age can be determined by the identification of formations, horizontality, and superposition.
3. sketch the confusingly titled unconformities such as an angular unconformity, nonconformity, and disconformity.
4. clearly restate the principle of cross-cutting relationships.
5. given two geographically separated formations, demonstrate stratigraphic correlation.
6. remind yourself about the relative geologic time scale you learned earlier in the course.
7. demonstrate your familiarity with the terminology of this time scale, by deciphering such terms as paleozoic and cenozoic.
8. define the term 'precambrian'.
9. explain the several ways in which atoms can go through radioactive decay and give off radiation as they become daughter products.
10. distinguish between alpha decay, beta decay, and electron capture.
11. demonstrate your skill with radioactive half-lives to determine the age of a rock when you are provided with the ratio of parent to daughter isotopes.
12. define the concept of effective time range.
13. explain in detail the mechanism by which carbon-14 can be used to age items which are less than 100,000 years old.
14. illustrate the manner in which cross-cutting relationships and radiometric dating an be used to age difficult scenarios.
15. evaluate the hypothesis provided by the Alvarezes regarding the K-T boundary, iridium, and mass extinction.
16. explain to a non-scientist friend the evidence that the earth is quite old; now try to explain the reliability of our best estimates of the age of the earth, solar system, and universe.
Critical Thinking Questions and Activities:
1. A zircon fragment is found within a granite pebble within a well-cemented conglomerate within a folded sequence of strata. The zircon is radiometrically dated at 1 billion years. What can you say about the age of the granite pebble? the relative age of the conglomerate? of the folded strata? What sequence of events can you deduce from these dates?