Geologic Time

5. the ratio between the number of parent and daughter isotopes is always ________.
6. matching rocks and fossils from sparate locations
7. an extremely thin coating of carbon on a rock
9. the preserved evidence activity of an organism
13. a time when a large proportion of Earth’s surface is covered by glaciers
14. the principle that in an undisturbed rock layer, the oldest rocks are on the bottom
15. a principle stating that geologic processes that occur today are similar to those that occured in the past
17. a major division on the geologic calendar; divided into periods
19. decay the process by which an unstable element naturally changes into another element that is stable
20. the age of rocks and geologic features compared with other nearby rocks and features

1. a piece of an older rock that becomes part of a new rock
2. is a fossil copy of an organism made when a mold of the organism is filled with sediment or mineral deposits
3. the study of Earth
4. the numerical age, in years, of a rock or object
8. when many types of living things become extinct at the same time
10. the preserved remains or evidence of past living organisms
11. atoms of the same element that have different numbers of
12. a surface where rock has eroded away, producing a break, or gap, in the rock record
16. a fossil representative of a species that existed on earth for a short length of time, was abundant, and inhabited many locations
18. the time required for half of the amount of a radioactive parent element to decay into a stable daughter element