Unit 4 Geologic Time Ch. 21 Sec. 3 & 4

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Across
  1. 5. remains of plants and animals that have been altered very little since the organisms' deaths
  2. 7. fossils that are easily recognized, abundant, and widely distributed geographically
  3. 8. created when a mold later becomes filled with material
  4. 12. scientist use C-14 to determine the age of organic materials, which contain abundant carbon
  5. 13. the pore spaces of an organism's buried hard parts are filled with minerals from groundwater
  6. 15. change in species over time
Down
  1. 1. scientists date an object using radioactive isotopes
  2. 2. shells, bones, or cell walls, are most common type of fossil, and can form from two processes
  3. 3. science of using tree rings to determine absolute age
  4. 4. emission of radioactive particles and the resulting change into other isotopes over time
  5. 6. indirect fossils, traces of worm trails, footprints, and tunneling burrows
  6. 9. length of time it takes for one half of the original parent isotope to decay
  7. 10. forms when sediments cover the original hard part of an organism such as shell, and the hard part is later removed by erosion or weathering
  8. 11. bands of alternating light and dark colored sediments of sand, clay, and silt
  9. 14. enables scientist to determine the numerical age of rocks and other objects