All about history

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Across
  1. 2. the period of time before this moment
  2. 4. how many main periods?
  3. 7. this moment now
  4. 8. the period of mammoths
Down
  1. 1. can help us measure time
  2. 3. period of now
  3. 4. the period after this moment
  4. 5. is 100 years
  5. 6. the study of human beings in the past
  6. 9. investigate the lives of people in different periods