Module 17 Fossils and the Rock Record

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Across
  1. 6. matching of rock outcrops of one geographic region to another
  2. 9. the change in species over time
  3. 10. the process where pore spaces of an organism's buried parts are filled in with minerals from groundwater
  4. 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
  5. 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
  6. 17. fossil whose soft organic material has been removed and whose hard parts have been changed by recrystallization or mineral replacement
  7. 18. determines the age of relatively young organic objects
  8. 20. record of Earth's history from its origin 4.6 bya to the present
  9. 21. gap in the rock record caused by erosion or weathering
  10. 23. fossil formed when an earlier fossil of a plant or animal leaves a cavity that becomes filled with minerals or sediment
  11. 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
  12. 26. the principle that an intrusion or fault is younger than the rock it cuts across
  13. 28. longest time unit in the geologic time scale
  14. 29. indirect fossil evidence of an organism
  15. 30. method that enables scientists to determine the actual age of certain rocks and other objects
  16. 31. describes a fossil with soft and hard parts that have undergone very little change since the organism's death
  17. 32. the principle that fragments, called inclusions, in a rock layer must be older than the rock layer that contains them
Down
  1. 1. the theory that geologic processes occurring today have been occurring since Earth formed
  2. 2. time unit in the geological time scale, smaller than a period, measured in hundreds of thousands to millions of years
  3. 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. 4. science of using tree rings to determine absolute age
  5. 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
  6. 7. occurs when an unusually large number of organisms disappear from the rock record at about the same time
  7. 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
  8. 12. the principle that states that an original sedimentary layer extends laterally until it tapers or thins at its edges
  9. 13. emission of radioactive particles and its resulting change into other isotopes over time
  10. 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
  11. 15. third-longest time unit in the geologic time scale, measured in tens of millions of years
  12. 19. establishing the order of past geologic events
  13. 22. informal unit of geologic time consisting of the first three eons during which Earth formed and became habitable
  14. 25. the principle that sedimentary rocks are deposited in horizontal or nearly horizontal layers
  15. 27. period of time it takes for a radioactive isotope, such as carbon-14, to decay to one-half of its original amount