Across
- 6. matching of rock outcrops of one geographic region to another
- 9. the change in species over time
- 10. the process where pore spaces of an organism's buried parts are filled in with minerals from groundwater
- 11. a rock or sediment layer that serves as a time marker in the rock record and results from volcanic ash or meteorite-impact debris that spread out and covered large areas of Earth
- 16. process used to determine the absolute age of a rock or fossil by determining the ratio of parent isotopes to daughter isotopes within a given sample
- 17. fossil whose soft organic material has been removed and whose hard parts have been changed by recrystallization or mineral replacement
- 18. determines the age of relatively young organic objects
- 20. record of Earth's history from its origin 4.6 bya to the present
- 21. gap in the rock record caused by erosion or weathering
- 23. fossil formed when an earlier fossil of a plant or animal leaves a cavity that becomes filled with minerals or sediment
- 24. the principle that, in an undisturbed rock sequence, the oldest rocks are on the bottom and each consecutive layer is younger than the layer beneath it
- 26. the principle that an intrusion or fault is younger than the rock it cuts across
- 28. longest time unit in the geologic time scale
- 29. indirect fossil evidence of an organism
- 30. method that enables scientists to determine the actual age of certain rocks and other objects
- 31. describes a fossil with soft and hard parts that have undergone very little change since the organism's death
- 32. the principle that fragments, called inclusions, in a rock layer must be older than the rock layer that contains them
Down
- 1. the theory that geologic processes occurring today have been occurring since Earth formed
- 2. time unit in the geological time scale, smaller than a period, measured in hundreds of thousands to millions of years
- 3. fossil that can form when a shelled organism decays in sedimentary rock and is removed by erosion or weathering, leaving a hollowed-out impression
- 4. science of using tree rings to determine absolute age
- 5. alternating light-colored and dark-colored sedimentary layers of sand, clay, and silt deposited in a lake that can be used to date cyclic events and changes in the environment
- 7. occurs when an unusually large number of organisms disappear from the rock record at about the same time
- 8. remains of plants or animals that were abundant, widely distributed, and existed briefly that can be used by geologists to correlate or date rock layers
- 12. the principle that states that an original sedimentary layer extends laterally until it tapers or thins at its edges
- 13. emission of radioactive particles and its resulting change into other isotopes over time
- 14. second-longest time unit in the geologic time scale, measured in tens to hundreds of millions of years, and defined by differences in life-forms that are preserved in rocks
- 15. third-longest time unit in the geologic time scale, measured in tens of millions of years
- 19. establishing the order of past geologic events
- 22. informal unit of geologic time consisting of the first three eons during which Earth formed and became habitable
- 25. the principle that sedimentary rocks are deposited in horizontal or nearly horizontal layers
- 27. period of time it takes for a radioactive isotope, such as carbon-14, to decay to one-half of its original amount