History of Life

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Across
  1. 2. 75% or more of ALL species on Earth go extinct within several million years
  2. 4. The theory that sedimentary rocks on the bottom are older than rocks on the top
  3. 6. Four-limbed animal
  4. 7. All organisms of that species is dead
  5. 10. Any remains, trace, or imprint of an organism that is preserved in Earth’s crust
  6. 13. Small particles are compacted and under pressure which forms rock over time
  7. 15. The normal, slow, natural loss of species (which is about 1-10 species per million, each year)
Down
  1. 1. Comparing the amounts of lead vs uranium in a rock sample since uranium-235 decays to lead
  2. 3. All of the fossils that have ever been found on Earth
  3. 5. Scientist who looks looks for and studies fossils
  4. 8. An organism that has a backbone and spinal cord
  5. 9. The variety of life that exists in a habitat/ecosystem
  6. 11. The study of fossils
  7. 12. Any living thing
  8. 14. Comparing amounts of carbon-14 and carbon-12 in a fossil to know how long ago the organism lived