Geologic Time Crossword

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Across
  1. 3. The science of determining the relative order of past events.
  2. 5. The beginning of a distinctive period.
  3. 7. Spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction.
  4. 8. The theory that changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes.
  5. 10. Subdivisions of geologic time.
  6. 11. The preserved remains or traces of animals, plants and other organisms from the past.
  7. 12. Time taken for the radioactivity of a specified isotope to fall to half its original value.
Down
  1. 1. A unit of time equal to 1 billion years.
  2. 2. Any method of determining the age of organic materials based on measurement of short-lived or long-lived radioactive elements.
  3. 4. A system of chronological dating that relates geological strata to time.
  4. 6. A method for determining the age of an object containing organic material by using the properties of radiocarbon.
  5. 9. A fossil that is good for dating and understanding the strata in which it is found.
  6. 13. A long and distinct period of history with a particular feature or characteristic.