Teacher Luke's amazing crossword puzzle

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Across
  1. 4. continent where humans first evolved
  2. 6. substance represented as Au on the periodic table
  3. 8. Surname of the 'King of Pop' who died in 2009
  4. 10. Julius Caesar was a ruler of which empire?
  5. 13. name of the main female character in the Harry Potter franchise
  6. 16. hydrocarbon liquid which powers the world
  7. 17. largest animal known to ever exist
  8. 18. Korean song that went viral in 2012
Down
  1. 1. most valuable cryptocurrency right now
  2. 2. name of the biggest ocean in the world
  3. 3. Bengal, Siberian, and sumatran are all types of what?
  4. 5. name of the current queen of England
  5. 7. name of the main Greek god
  6. 9. domesticated wolf
  7. 11. biggest city in Japan
  8. 12. name of the person with the world record for 100m sprint
  9. 14. largest country in the world
  10. 15. name of the person who uses a whistle in most sports