Across
- 1. process of studying the order in which the geologic events occurred
- 4. geological processes occurring today have been occurring since Earth formed
- 5. eon with the most fossils
- 6. record of Earth's history from its origin 4.6 billion years ago to present
- 7. oldest 3 eons that make up 90% of geologic time
- 11. third largest unit of time
- 14. the mold left by an organism is filled by new material and sediments
- 16. organism is buried in sediments then decays and leaves a hallow space
- 17. recent life
- 19. process of determining the numerical age of rocks and other objects
- 22. buried surfaces of erosion
- 25. middle life
- 27. when scientists date an object using radioactive isotopes
- 29. in an undisturbed rock sequence the oldest rocks are at the bottom and younger at top
Down
- 2. an index fossil for the paleozoic era
- 3. unstable elements that emit particle called radiation
- 8. smallest division of time
- 9. sedimentary rocks are deposited in horizontal layers
- 10. an intrusion or fault is younger than the rock it cuts across
- 12. old life
- 13. a type of fossil that is just evidence of an organism like a footprint
- 15. second largest unit of time
- 18. amount of time it take for one-half of the original parent isotope to decay
- 20. largest of the time units
- 21. a fossil used to determine a relative age of a rock
- 23. the fragment in a rock layer must be older than the rock layer that contains them
- 24. matching rock outcrops or fossils exposed in one area to similar fossils and outcrops in another
- 25. type of organisms that were most prevalent during the paleozoic era.
- 26. used to date rocks less than 60,000 years old
- 28. remains and traces or imprints of ancient organisms