Earth's History & Geologic Time

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Across
  1. 2. A danish geologist who came up with the laws of stratigraphy
  2. 5. ________ Dating, finding the exact age of a rock
  3. 9. atomic mass of electrons
  4. 10. Unstable, doesn't like to exist in nature, will decay
  5. 13. The amount of time it takes for half of the radioactive isotopes to decay
  6. 15. The number of mass extinctions in Earth's history
  7. 16. How we refer to the radioactive, non-decayed isotope
  8. 19. Atomic mass of protons and neutrons
  9. 20. The principle of crosscutting relationships says that these must be younger than any impacted layer
Down
  1. 1. The principle of original __________, says that rock layers form flat
  2. 2. The law that says layers close to the surface must have formed most recently
  3. 3. The separation into layers by relative density
  4. 4. ________ dating; establishing the correct order of formation in rock layers
  5. 6. A unit of geologic time that lasts tens of millions of years
  6. 7. A mass extinction is when ____% of species on earth die out at one time
  7. 8. The second longest unit of geologic time
  8. 11. Atoms with different numbers of neutrons
  9. 12. How we refer to the stable, decayed isotope
  10. 14. The shortest unit of geologic time
  11. 17. The longest unit of geologic time
  12. 18. The earth formed 4.55 ____________ years ago