Geologic Time Scale

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Across
  1. 5. A sedimentary rock formed from marine organisms.
  2. 7. Oxygen-producing organisms.
  3. 8. Earliest part of Earth's history.
  4. 10. A long and distinc phase of history.
  5. 11. An era marked by early life forms.
Down
  1. 1. To arrange or put in order.
  2. 2. A system fo chronological dating for Earth's history.
  3. 3. The most recent geological period.
  4. 4. To improve something by making small changes.
  5. 6. A length of time with a specific characteristic.
  6. 7. Era known for the rise of mammals.
  7. 9. The age of dinosaurs.