Geologic Time Scale Vocabulary

3. a principle that geologic processes that occurred in the past can be explained by current geologic processes
5. the weather conditions in an area over a long period of time
7. the scientific study of the origin, history, and structure of Earth and the processes that shape Earth
10. a principle that states that younger rocks lie above older rocks if the layers have not been disturbed
12. the standard method used to divide Earth's long natural history into manageable parts
13. a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time

1. the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock
2. the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope
4. any method of determining whether an event or object is older or younger than other events or objects
6. any method of measuring the age of an event or object in years
8. an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom
9. the process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element
11. a long cylinder of ice obtained from drilling through ice caps or ice sheets; used to study past climates