History of the Earth

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Across
  1. 4. a principle that something has to be in existence
  2. 6. a gap in the geologic record of rock layers
  3. 8. a burrow, or scat
  4. 9. a material made up of the same type of atom
  5. 13. the breakdown of a radioactive element resulting in the release of particles and energy
  6. 15. the principle that sedimentary rocks were originally
  7. 16. organism’s body
  8. 20. something can happen to it
  9. 21. the element that forms when a parent element undergoes radioactive decay
  10. 23. substance to decay
  11. 27. a scientist who studies fossils
  12. 28. a method for dating ancient igneous rocks that compares the amount of potassium to the amount of argon
  13. 29. the time it takes for half the atoms in a sample of an
Down
  1. 1. a radioactive element that decays to form a daughter
  2. 2. a tiny particle that is considered the building block of all
  3. 3. years
  4. 4. a method for dating things that were alive in the past
  5. 5. in horizontal layers
  6. 7. a fossil of an organism’s activity, such as a
  7. 10. an organism whose remains have been replaced
  8. 11. the extinction of a large number of species in a
  9. 12. amount of time
  10. 14. a hollow fossil that marks the shape of an
  11. 17. a fossil copy of the original organism
  12. 18. time by minerals
  13. 19. a rock with a coating of only the carbon from an
  14. 22. of the cooling of lava
  15. 24. the exact age of something
  16. 25. a comparison of the age of one thing to the age of
  17. 26. igneous rock that forms at Earth’s surface as a