Across
- 2. a gap in the geologic rock record
- 5. an ordered arrangement of rock layers that is based on the relative ages of the rocks
- 7. the average weather conditions in an area over a long period of time
- 10. the principal that states younger rocks lie above older rocks
- 11. determining the age of an event or object in years
- 13. a long cylinder of ice
- 15. the breakdown of a radioactive isotope into a stable isotope
- 16. Earth's long natural history is divided into time units
- 17. is the trace or remains of an organism that lived long ago
- 18. the process of determining whether an object or event is older or younger than other objects or events
Down
- 1. the smallest units of geologic time
- 3. theory that the continents were once together and moved apart over time
- 4. eras are divided into.....which usually cover tens of millions of years
- 6. finding the absolute age of a sample by determining the percentage of a radioactive parent isotope and a stable daughter isotope
- 8. the largest division of geologic time
- 9. the average time needed for half of a sample of a radioactive isotope to undergo decay
- 12. a fossilized structure that was formed in sedimentary rock by animal activity
- 14. Eons are subdivided into smaller units called.....