Fossil and Rock Record

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Across
  1. 2. a fossil that is found in the rock layers of only one geologic age and that is used to establish the age of the rock layers
  2. 3. an atom that has the same number of protons as the other atoms of the same element do but that has different number of neutrons
  3. 5. the time needed for half of a sample of radioactive substance to undergo decay
  4. 6. column an arrangement of rock layers in which the oldest rocks are at the bottom
  5. 8. a method of determining the age of an object by estimating the relative percentages of radioactive isotope and a stable isotope
  6. 9. a fossilized mark that formed in soft sediment by the movement of an animal
  7. 13. a type of fossil that forms when sediments fill in the cavity left by a decomposed organism
  8. 14. a process that states geological processes that occurred in the past can be explained by current geologic processes
  9. 15. a mark or cavity made in a sedimentary surface by a shell or other body
  10. 16. a break in the logic record created when rock layers are eroded or when sediment is not deposited for a long period of time
Down
  1. 1. any method of measuring the age of an event or object in years
  2. 4. a principle that states that younger rocks lie above older rocks if the layers have not been disturbed
  3. 7. a principle that states that geologic change occurs suddenly
  4. 10. any method of determining whether an event or object is older or younger than other events or objects
  5. 11. scientific study of fossils
  6. 12. the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock